This is sed.info, produced by makeinfo version 6.8dev from sed.texi. This file documents version 4.9 of GNU ‘sed’, a stream editor. Copyright © 1998–2022 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License”. INFO-DIR-SECTION Text creation and manipulation START-INFO-DIR-ENTRY * sed: (sed). Stream EDitor. END-INFO-DIR-ENTRY  File: sed.info, Node: Top, Next: Introduction, Up: (dir) GNU ‘sed’ ********* This file documents version 4.9 of GNU ‘sed’, a stream editor. Copyright © 1998–2022 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License”. * Menu: * Introduction:: Introduction * Invoking sed:: Invocation * sed scripts:: ‘sed’ scripts * sed addresses:: Addresses: selecting lines * sed regular expressions:: Regular expressions: selecting text * advanced sed:: Advanced ‘sed’: cycles and buffers * Examples:: Some sample scripts * Limitations:: Limitations and (non-)limitations of GNU ‘sed’ * Other Resources:: Other resources for learning about ‘sed’ * Reporting Bugs:: Reporting bugs * GNU Free Documentation License:: Copying and sharing this manual * Concept Index:: A menu with all the topics in this manual. * Command and Option Index:: A menu with all ‘sed’ commands and command-line options.  File: sed.info, Node: Introduction, Next: Invoking sed, Prev: Top, Up: Top 1 Introduction ************** ‘sed’ is a stream editor. A stream editor is used to perform basic text transformations on an input stream (a file or input from a pipeline). While in some ways similar to an editor which permits scripted edits (such as ‘ed’), ‘sed’ works by making only one pass over the input(s), and is consequently more efficient. But it is ‘sed’’s ability to filter text in a pipeline which particularly distinguishes it from other types of editors.  File: sed.info, Node: Invoking sed, Next: sed scripts, Prev: Introduction, Up: Top 2 Running sed ************* This chapter covers how to run ‘sed’. Details of ‘sed’ scripts and individual ‘sed’ commands are discussed in the next chapter. * Menu: * Overview:: * Command-Line Options:: * Exit status::  File: sed.info, Node: Overview, Next: Command-Line Options, Up: Invoking sed 2.1 Overview ============ Normally ‘sed’ is invoked like this: sed SCRIPT INPUTFILE... For example, to change every ‘hello’ to ‘world’ in the file ‘input.txt’: sed 's/hello/world/g' input.txt > output.txt Without the ‘g’ (global) modifier, ‘sed’ affects only the first instance per line. If you do not specify INPUTFILE, or if INPUTFILE is ‘-’, ‘sed’ filters the contents of the standard input. The following commands are equivalent: sed 's/hello/world/g' input.txt > output.txt sed 's/hello/world/g' < input.txt > output.txt cat input.txt | sed 's/hello/world/g' - > output.txt ‘sed’ writes output to standard output. Use ‘-i’ to edit files in-place instead of printing to standard output. See also the ‘W’ and ‘s///w’ commands for writing output to other files. The following command modifies ‘file.txt’ and does not produce any output: sed -i 's/hello/world/' file.txt By default ‘sed’ prints all processed input (except input that has been modified/deleted by commands such as ‘d’). Use ‘-n’ to suppress output, and the ‘p’ command to print specific lines. The following command prints only line 45 of the input file: sed -n '45p' file.txt ‘sed’ treats multiple input files as one long stream. The following example prints the first line of the first file (‘one.txt’) and the last line of the last file (‘three.txt’). Use ‘-s’ to reverse this behavior. sed -n '1p ; $p' one.txt two.txt three.txt Without ‘-e’ or ‘-f’ options, ‘sed’ uses the first non-option parameter as the SCRIPT, and the following non-option parameters as input files. If ‘-e’ or ‘-f’ options are used to specify a SCRIPT, all non-option parameters are taken as input files. Options ‘-e’ and ‘-f’ can be combined, and can appear multiple times (in which case the final effective SCRIPT will be concatenation of all the individual SCRIPTs). The following examples are equivalent: sed 's/hello/world/' input.txt > output.txt sed -e 's/hello/world/' input.txt > output.txt sed --expression='s/hello/world/' input.txt > output.txt echo 's/hello/world/' > myscript.sed sed -f myscript.sed input.txt > output.txt sed --file=myscript.sed input.txt > output.txt  File: sed.info, Node: Command-Line Options, Next: Exit status, Prev: Overview, Up: Invoking sed 2.2 Command-Line Options ======================== The full format for invoking ‘sed’ is: sed OPTIONS... [SCRIPT] [INPUTFILE...] ‘sed’ may be invoked with the following command-line options: ‘--version’ Print out the version of ‘sed’ that is being run and a copyright notice, then exit. ‘--help’ Print a usage message briefly summarizing these command-line options and the bug-reporting address, then exit. ‘-n’ ‘--quiet’ ‘--silent’ By default, ‘sed’ prints out the pattern space at the end of each cycle through the script (*note How ‘sed’ works: Execution Cycle.). These options disable this automatic printing, and ‘sed’ only produces output when explicitly told to via the ‘p’ command. ‘--debug’ Print the input sed program in canonical form, and annotate program execution. $ echo 1 | sed '\%1%s21232' 3 $ echo 1 | sed --debug '\%1%s21232' SED PROGRAM: /1/ s/1/3/ INPUT: 'STDIN' line 1 PATTERN: 1 COMMAND: /1/ s/1/3/ PATTERN: 3 END-OF-CYCLE: 3 ‘-e SCRIPT’ ‘--expression=SCRIPT’ Add the commands in SCRIPT to the set of commands to be run while processing the input. ‘-f SCRIPT-FILE’ ‘--file=SCRIPT-FILE’ Add the commands contained in the file SCRIPT-FILE to the set of commands to be run while processing the input. ‘-i[SUFFIX]’ ‘--in-place[=SUFFIX]’ This option specifies that files are to be edited in-place. GNU ‘sed’ does this by creating a temporary file and sending output to this file rather than to the standard output.(1). This option implies ‘-s’. When the end of the file is reached, the temporary file is renamed to the output file’s original name. The extension, if supplied, is used to modify the name of the old file before renaming the temporary file, thereby making a backup copy(2)). This rule is followed: if the extension doesn’t contain a ‘*’, then it is appended to the end of the current filename as a suffix; if the extension does contain one or more ‘*’ characters, then _each_ asterisk is replaced with the current filename. This allows you to add a prefix to the backup file, instead of (or in addition to) a suffix, or even to place backup copies of the original files into another directory (provided the directory already exists). If no extension is supplied, the original file is overwritten without making a backup. Because ‘-i’ takes an optional argument, it should not be followed by other short options: ‘sed -Ei '...' FILE’ Same as ‘-E -i’ with no backup suffix - ‘FILE’ will be edited in-place without creating a backup. ‘sed -iE '...' FILE’ This is equivalent to ‘--in-place=E’, creating ‘FILEE’ as backup of ‘FILE’ Be cautious of using ‘-n’ with ‘-i’: the former disables automatic printing of lines and the latter changes the file in-place without a backup. Used carelessly (and without an explicit ‘p’ command), the output file will be empty: # WRONG USAGE: 'FILE' will be truncated. sed -ni 's/foo/bar/' FILE ‘-l N’ ‘--line-length=N’ Specify the default line-wrap length for the ‘l’ command. A length of 0 (zero) means to never wrap long lines. If not specified, it is taken to be 70. ‘--posix’ GNU ‘sed’ includes several extensions to POSIX sed. In order to simplify writing portable scripts, this option disables all the extensions that this manual documents, including additional commands. Most of the extensions accept ‘sed’ programs that are outside the syntax mandated by POSIX, but some of them (such as the behavior of the ‘N’ command described in *note Reporting Bugs::) actually violate the standard. If you want to disable only the latter kind of extension, you can set the ‘POSIXLY_CORRECT’ variable to a non-empty value. ‘-b’ ‘--binary’ This option is available on every platform, but is only effective where the operating system makes a distinction between text files and binary files. When such a distinction is made—as is the case for MS-DOS, Windows, Cygwin—text files are composed of lines separated by a carriage return _and_ a line feed character, and ‘sed’ does not see the ending CR. When this option is specified, ‘sed’ will open input files in binary mode, thus not requesting this special processing and considering lines to end at a line feed. ‘--follow-symlinks’ This option is available only on platforms that support symbolic links and has an effect only if option ‘-i’ is specified. In this case, if the file that is specified on the command line is a symbolic link, ‘sed’ will follow the link and edit the ultimate destination of the link. The default behavior is to break the symbolic link, so that the link destination will not be modified. ‘-E’ ‘-r’ ‘--regexp-extended’ Use extended regular expressions rather than basic regular expressions. Extended regexps are those that ‘egrep’ accepts; they can be clearer because they usually have fewer backslashes. Historically this was a GNU extension, but the ‘-E’ extension has since been added to the POSIX standard (http://austingroupbugs.net/view.php?id=528), so use ‘-E’ for portability. GNU sed has accepted ‘-E’ as an undocumented option for years, and *BSD seds have accepted ‘-E’ for years as well, but scripts that use ‘-E’ might not port to other older systems. *Note Extended regular expressions: ERE syntax. ‘-s’ ‘--separate’ By default, ‘sed’ will consider the files specified on the command line as a single continuous long stream. This GNU ‘sed’ extension allows the user to consider them as separate files: range addresses (such as ‘/abc/,/def/’) are not allowed to span several files, line numbers are relative to the start of each file, ‘$’ refers to the last line of each file, and files invoked from the ‘R’ commands are rewound at the start of each file. ‘--sandbox’ In sandbox mode, ‘e/w/r’ commands are rejected - programs containing them will be aborted without being run. Sandbox mode ensures ‘sed’ operates only on the input files designated on the command line, and cannot run external programs. ‘-u’ ‘--unbuffered’ Buffer both input and output as minimally as practical. (This is particularly useful if the input is coming from the likes of ‘tail -f’, and you wish to see the transformed output as soon as possible.) ‘-z’ ‘--null-data’ ‘--zero-terminated’ Treat the input as a set of lines, each terminated by a zero byte (the ASCII ‘NUL’ character) instead of a newline. This option can be used with commands like ‘sort -z’ and ‘find -print0’ to process arbitrary file names. If no ‘-e’, ‘-f’, ‘--expression’, or ‘--file’ options are given on the command-line, then the first non-option argument on the command line is taken to be the SCRIPT to be executed. If any command-line parameters remain after processing the above, these parameters are interpreted as the names of input files to be processed. A file name of ‘-’ refers to the standard input stream. The standard input will be processed if no file names are specified. ---------- Footnotes ---------- (1) This applies to commands such as ‘=’, ‘a’, ‘c’, ‘i’, ‘l’, ‘p’. You can still write to the standard output by using the ‘w’ or ‘W’ commands together with the ‘/dev/stdout’ special file (2) Note that GNU ‘sed’ creates the backup file whether or not any output is actually changed.  File: sed.info, Node: Exit status, Prev: Command-Line Options, Up: Invoking sed 2.3 Exit status =============== An exit status of zero indicates success, and a nonzero value indicates failure. GNU ‘sed’ returns the following exit status error values: 0 Successful completion. 1 Invalid command, invalid syntax, invalid regular expression or a GNU ‘sed’ extension command used with ‘--posix’. 2 One or more of the input file specified on the command line could not be opened (e.g. if a file is not found, or read permission is denied). Processing continued with other files. 4 An I/O error, or a serious processing error during runtime, GNU ‘sed’ aborted immediately. Additionally, the commands ‘q’ and ‘Q’ can be used to terminate ‘sed’ with a custom exit code value (this is a GNU ‘sed’ extension): $ echo | sed 'Q42' ; echo $? 42  File: sed.info, Node: sed scripts, Next: sed addresses, Prev: Invoking sed, Up: Top 3 ‘sed’ scripts *************** * Menu: * sed script overview:: ‘sed’ script overview * sed commands list:: ‘sed’ commands summary * The "s" Command:: ‘sed’’s Swiss Army Knife * Common Commands:: Often used commands * Other Commands:: Less frequently used commands * Programming Commands:: Commands for ‘sed’ gurus * Extended Commands:: Commands specific of GNU ‘sed’ * Multiple commands syntax:: Extension for easier scripting  File: sed.info, Node: sed script overview, Next: sed commands list, Up: sed scripts 3.1 ‘sed’ script overview ========================= A ‘sed’ program consists of one or more ‘sed’ commands, passed in by one or more of the ‘-e’, ‘-f’, ‘--expression’, and ‘--file’ options, or the first non-option argument if zero of these options are used. This document will refer to “the” ‘sed’ script; this is understood to mean the in-order concatenation of all of the SCRIPTs and SCRIPT-FILEs passed in. *Note Overview::. ‘sed’ commands follow this syntax: [addr]X[options] X is a single-letter ‘sed’ command. ‘[addr]’ is an optional line address. If ‘[addr]’ is specified, the command X will be executed only on the matched lines. ‘[addr]’ can be a single line number, a regular expression, or a range of lines (*note sed addresses::). Additional ‘[options]’ are used for some ‘sed’ commands. The following example deletes lines 30 to 35 in the input. ‘30,35’ is an address range. ‘d’ is the delete command: sed '30,35d' input.txt > output.txt The following example prints all input until a line starting with the string ‘foo’ is found. If such line is found, ‘sed’ will terminate with exit status 42. If such line was not found (and no other error occurred), ‘sed’ will exit with status 0. ‘/^foo/’ is a regular-expression address. ‘q’ is the quit command. ‘42’ is the command option. sed '/^foo/q42' input.txt > output.txt Commands within a SCRIPT or SCRIPT-FILE can be separated by semicolons (‘;’) or newlines (ASCII 10). Multiple scripts can be specified with ‘-e’ or ‘-f’ options. The following examples are all equivalent. They perform two ‘sed’ operations: deleting any lines matching the regular expression ‘/^foo/’, and replacing all occurrences of the string ‘hello’ with ‘world’: sed '/^foo/d ; s/hello/world/g' input.txt > output.txt sed -e '/^foo/d' -e 's/hello/world/g' input.txt > output.txt echo '/^foo/d' > script.sed echo 's/hello/world/g' >> script.sed sed -f script.sed input.txt > output.txt echo 's/hello/world/g' > script2.sed sed -e '/^foo/d' -f script2.sed input.txt > output.txt Commands ‘a’, ‘c’, ‘i’, due to their syntax, cannot be followed by semicolons working as command separators and thus should be terminated with newlines or be placed at the end of a SCRIPT or SCRIPT-FILE. Commands can also be preceded with optional non-significant whitespace characters. *Note Multiple commands syntax::.  File: sed.info, Node: sed commands list, Next: The "s" Command, Prev: sed script overview, Up: sed scripts 3.2 ‘sed’ commands summary ========================== The following commands are supported in GNU ‘sed’. Some are standard POSIX commands, while other are GNU extensions. Details and examples for each command are in the following sections. (Mnemonics) are shown in parentheses. ‘a\’ ‘TEXT’ Append TEXT after a line. ‘a TEXT’ Append TEXT after a line (alternative syntax). ‘b LABEL’ Branch unconditionally to LABEL. The LABEL may be omitted, in which case the next cycle is started. ‘c\’ ‘TEXT’ Replace (change) lines with TEXT. ‘c TEXT’ Replace (change) lines with TEXT (alternative syntax). ‘d’ Delete the pattern space; immediately start next cycle. ‘D’ If pattern space contains newlines, delete text in the pattern space up to the first newline, and restart cycle with the resultant pattern space, without reading a new line of input. If pattern space contains no newline, start a normal new cycle as if the ‘d’ command was issued. ‘e’ Executes the command that is found in pattern space and replaces the pattern space with the output; a trailing newline is suppressed. ‘e COMMAND’ Executes COMMAND and sends its output to the output stream. The command can run across multiple lines, all but the last ending with a back-slash. ‘F’ (filename) Print the file name of the current input file (with a trailing newline). ‘g’ Replace the contents of the pattern space with the contents of the hold space. ‘G’ Append a newline to the contents of the pattern space, and then append the contents of the hold space to that of the pattern space. ‘h’ (hold) Replace the contents of the hold space with the contents of the pattern space. ‘H’ Append a newline to the contents of the hold space, and then append the contents of the pattern space to that of the hold space. ‘i\’ ‘TEXT’ insert TEXT before a line. ‘i TEXT’ insert TEXT before a line (alternative syntax). ‘l’ Print the pattern space in an unambiguous form. ‘n’ (next) If auto-print is not disabled, print the pattern space, then, regardless, replace the pattern space with the next line of input. If there is no more input then ‘sed’ exits without processing any more commands. ‘N’ Add a newline to the pattern space, then append the next line of input to the pattern space. If there is no more input then ‘sed’ exits without processing any more commands. ‘p’ Print the pattern space. ‘P’ Print the pattern space, up to the first . ‘q[EXIT-CODE]’ (quit) Exit ‘sed’ without processing any more commands or input. ‘Q[EXIT-CODE]’ (quit) This command is the same as ‘q’, but will not print the contents of pattern space. Like ‘q’, it provides the ability to return an exit code to the caller. ‘r filename’ Reads file FILENAME. ‘R filename’ Queue a line of FILENAME to be read and inserted into the output stream at the end of the current cycle, or when the next input line is read. ‘s/REGEXP/REPLACEMENT/[FLAGS]’ (substitute) Match the regular-expression against the content of the pattern space. If found, replace matched string with REPLACEMENT. ‘t LABEL’ (test) Branch to LABEL only if there has been a successful ‘s’ubstitution since the last input line was read or conditional branch was taken. The LABEL may be omitted, in which case the next cycle is started. ‘T LABEL’ (test) Branch to LABEL only if there have been no successful ‘s’ubstitutions since the last input line was read or conditional branch was taken. The LABEL may be omitted, in which case the next cycle is started. ‘v [VERSION]’ (version) This command does nothing, but makes ‘sed’ fail if GNU ‘sed’ extensions are not supported, or if the requested version is not available. ‘w filename’ Write the pattern space to FILENAME. ‘W filename’ Write to the given filename the portion of the pattern space up to the first newline ‘x’ Exchange the contents of the hold and pattern spaces. ‘y/src/dst/’ Transliterate any characters in the pattern space which match any of the SOURCE-CHARS with the corresponding character in DEST-CHARS. ‘z’ (zap) This command empties the content of pattern space. ‘#’ A comment, until the next newline. ‘{ CMD ; CMD ... }’ Group several commands together. ‘=’ Print the current input line number (with a trailing newline). ‘: LABEL’ Specify the location of LABEL for branch commands (‘b’, ‘t’, ‘T’).  File: sed.info, Node: The "s" Command, Next: Common Commands, Prev: sed commands list, Up: sed scripts 3.3 The ‘s’ Command =================== The ‘s’ command (as in substitute) is probably the most important in ‘sed’ and has a lot of different options. The syntax of the ‘s’ command is ‘s/REGEXP/REPLACEMENT/FLAGS’. Its basic concept is simple: the ‘s’ command attempts to match the pattern space against the supplied regular expression REGEXP; if the match is successful, then that portion of the pattern space which was matched is replaced with REPLACEMENT. For details about REGEXP syntax *note Regular Expression Addresses: Regexp Addresses. The REPLACEMENT can contain ‘\N’ (N being a number from 1 to 9, inclusive) references, which refer to the portion of the match which is contained between the Nth ‘\(’ and its matching ‘\)’. Also, the REPLACEMENT can contain unescaped ‘&’ characters which reference the whole matched portion of the pattern space. The ‘/’ characters may be uniformly replaced by any other single character within any given ‘s’ command. The ‘/’ character (or whatever other character is used in its stead) can appear in the REGEXP or REPLACEMENT only if it is preceded by a ‘\’ character. Finally, as a GNU ‘sed’ extension, you can include a special sequence made of a backslash and one of the letters ‘L’, ‘l’, ‘U’, ‘u’, or ‘E’. The meaning is as follows: ‘\L’ Turn the replacement to lowercase until a ‘\U’ or ‘\E’ is found, ‘\l’ Turn the next character to lowercase, ‘\U’ Turn the replacement to uppercase until a ‘\L’ or ‘\E’ is found, ‘\u’ Turn the next character to uppercase, ‘\E’ Stop case conversion started by ‘\L’ or ‘\U’. When the ‘g’ flag is being used, case conversion does not propagate from one occurrence of the regular expression to another. For example, when the following command is executed with ‘a-b-’ in pattern space: s/\(b\?\)-/x\u\1/g the output is ‘axxB’. When replacing the first ‘-’, the ‘\u’ sequence only affects the empty replacement of ‘\1’. It does not affect the ‘x’ character that is added to pattern space when replacing ‘b-’ with ‘xB’. On the other hand, ‘\l’ and ‘\u’ do affect the remainder of the replacement text if they are followed by an empty substitution. With ‘a-b-’ in pattern space, the following command: s/\(b\?\)-/\u\1x/g will replace ‘-’ with ‘X’ (uppercase) and ‘b-’ with ‘Bx’. If this behavior is undesirable, you can prevent it by adding a ‘\E’ sequence—after ‘\1’ in this case. To include a literal ‘\’, ‘&’, or newline in the final replacement, be sure to precede the desired ‘\’, ‘&’, or newline in the REPLACEMENT with a ‘\’. The ‘s’ command can be followed by zero or more of the following FLAGS: ‘g’ Apply the replacement to _all_ matches to the REGEXP, not just the first. ‘NUMBER’ Only replace the NUMBERth match of the REGEXP. interaction in ‘s’ command Note: the POSIX standard does not specify what should happen when you mix the ‘g’ and NUMBER modifiers, and currently there is no widely agreed upon meaning across ‘sed’ implementations. For GNU ‘sed’, the interaction is defined to be: ignore matches before the NUMBERth, and then match and replace all matches from the NUMBERth on. ‘p’ If the substitution was made, then print the new pattern space. Note: when both the ‘p’ and ‘e’ options are specified, the relative ordering of the two produces very different results. In general, ‘ep’ (evaluate then print) is what you want, but operating the other way round can be useful for debugging. For this reason, the current version of GNU ‘sed’ interprets specially the presence of ‘p’ options both before and after ‘e’, printing the pattern space before and after evaluation, while in general flags for the ‘s’ command show their effect just once. This behavior, although documented, might change in future versions. ‘w FILENAME’ If the substitution was made, then write out the result to the named file. As a GNU ‘sed’ extension, two special values of FILENAME are supported: ‘/dev/stderr’, which writes the result to the standard error, and ‘/dev/stdout’, which writes to the standard output.(1) ‘e’ This command allows one to pipe input from a shell command into pattern space. If a substitution was made, the command that is found in pattern space is executed and pattern space is replaced with its output. A trailing newline is suppressed; results are undefined if the command to be executed contains a NUL character. This is a GNU ‘sed’ extension. ‘I’ ‘i’ The ‘I’ modifier to regular-expression matching is a GNU extension which makes ‘sed’ match REGEXP in a case-insensitive manner. ‘M’ ‘m’ The ‘M’ modifier to regular-expression matching is a GNU ‘sed’ extension which directs GNU ‘sed’ to match the regular expression in ‘multi-line’ mode. The modifier causes ‘^’ and ‘$’ to match respectively (in addition to the normal behavior) the empty string after a newline, and the empty string before a newline. There are special character sequences (‘\`’ and ‘\'’) which always match the beginning or the end of the buffer. In addition, the period character does not match a new-line character in multi-line mode. ---------- Footnotes ---------- (1) This is equivalent to ‘p’ unless the ‘-i’ option is being used.  File: sed.info, Node: Common Commands, Next: Other Commands, Prev: The "s" Command, Up: sed scripts 3.4 Often-Used Commands ======================= If you use ‘sed’ at all, you will quite likely want to know these commands. ‘#’ [No addresses allowed.] The ‘#’ character begins a comment; the comment continues until the next newline. If you are concerned about portability, be aware that some implementations of ‘sed’ (which are not POSIX conforming) may only support a single one-line comment, and then only when the very first character of the script is a ‘#’. Warning: if the first two characters of the ‘sed’ script are ‘#n’, then the ‘-n’ (no-autoprint) option is forced. If you want to put a comment in the first line of your script and that comment begins with the letter ‘n’ and you do not want this behavior, then be sure to either use a capital ‘N’, or place at least one space before the ‘n’. ‘q [EXIT-CODE]’ Exit ‘sed’ without processing any more commands or input. Example: stop after printing the second line: $ seq 3 | sed 2q 1 2 This command accepts only one address. Note that the current pattern space is printed if auto-print is not disabled with the ‘-n’ options. The ability to return an exit code from the ‘sed’ script is a GNU ‘sed’ extension. See also the GNU ‘sed’ extension ‘Q’ command which quits silently without printing the current pattern space. ‘d’ Delete the pattern space; immediately start next cycle. Example: delete the second input line: $ seq 3 | sed 2d 1 3 ‘p’ Print out the pattern space (to the standard output). This command is usually only used in conjunction with the ‘-n’ command-line option. Example: print only the second input line: $ seq 3 | sed -n 2p 2 ‘n’ If auto-print is not disabled, print the pattern space, then, regardless, replace the pattern space with the next line of input. If there is no more input then ‘sed’ exits without processing any more commands. This command is useful to skip lines (e.g. process every Nth line). Example: perform substitution on every 3rd line (i.e. two ‘n’ commands skip two lines): $ seq 6 | sed 'n;n;s/./x/' 1 2 x 4 5 x GNU ‘sed’ provides an extension address syntax of FIRST~STEP to achieve the same result: $ seq 6 | sed '0~3s/./x/' 1 2 x 4 5 x ‘{ COMMANDS }’ A group of commands may be enclosed between ‘{’ and ‘}’ characters. This is particularly useful when you want a group of commands to be triggered by a single address (or address-range) match. Example: perform substitution then print the second input line: $ seq 3 | sed -n '2{s/2/X/ ; p}' X  File: sed.info, Node: Other Commands, Next: Programming Commands, Prev: Common Commands, Up: sed scripts 3.5 Less Frequently-Used Commands ================================= Though perhaps less frequently used than those in the previous section, some very small yet useful ‘sed’ scripts can be built with these commands. ‘y/SOURCE-CHARS/DEST-CHARS/’ Transliterate any characters in the pattern space which match any of the SOURCE-CHARS with the corresponding character in DEST-CHARS. Example: transliterate ‘a-j’ into ‘0-9’: $ echo hello world | sed 'y/abcdefghij/0123456789/' 74llo worl3 (The ‘/’ characters may be uniformly replaced by any other single character within any given ‘y’ command.) Instances of the ‘/’ (or whatever other character is used in its stead), ‘\’, or newlines can appear in the SOURCE-CHARS or DEST-CHARS lists, provide that each instance is escaped by a ‘\’. The SOURCE-CHARS and DEST-CHARS lists _must_ contain the same number of characters (after de-escaping). See the ‘tr’ command from GNU coreutils for similar functionality. ‘a TEXT’ Appending TEXT after a line. This is a GNU extension to the standard ‘a’ command - see below for details. Example: Add ‘hello’ after the second line: $ seq 3 | sed '2a hello' 1 2 hello 3 Leading whitespace after the ‘a’ command is ignored. The text to add is read until the end of the line. ‘a\’ ‘TEXT’ Appending TEXT after a line. Example: Add ‘hello’ after the second line (⊣ indicates printed output lines): $ seq 3 | sed '2a\ hello' ⊣1 ⊣2 ⊣hello ⊣3 The ‘a’ command queues the lines of text which follow this command (each but the last ending with a ‘\’, which are removed from the output) to be output at the end of the current cycle, or when the next input line is read. As a GNU extension, this command accepts two addresses. Escape sequences in TEXT are processed, so you should use ‘\\’ in TEXT to print a single backslash. The commands resume after the last line without a backslash (‘\’) - ‘world’ in the following example: $ seq 3 | sed '2a\ hello\ world 3s/./X/' ⊣1 ⊣2 ⊣hello ⊣world ⊣X As a GNU extension, the ‘a’ command and TEXT can be separated into two ‘-e’ parameters, enabling easier scripting: $ seq 3 | sed -e '2a\' -e hello 1 2 hello 3 $ sed -e '2a\' -e "$VAR" ‘i TEXT’ insert TEXT before a line. This is a GNU extension to the standard ‘i’ command - see below for details. Example: Insert ‘hello’ before the second line: $ seq 3 | sed '2i hello' 1 hello 2 3 Leading whitespace after the ‘i’ command is ignored. The text to add is read until the end of the line. ‘i\’ ‘TEXT’ Immediately output the lines of text which follow this command. Example: Insert ‘hello’ before the second line (⊣ indicates printed output lines): $ seq 3 | sed '2i\ hello' ⊣1 ⊣hello ⊣2 ⊣3 As a GNU extension, this command accepts two addresses. Escape sequences in TEXT are processed, so you should use ‘\\’ in TEXT to print a single backslash. The commands resume after the last line without a backslash (‘\’) - ‘world’ in the following example: $ seq 3 | sed '2i\ hello\ world s/./X/' ⊣X ⊣hello ⊣world ⊣X ⊣X As a GNU extension, the ‘i’ command and TEXT can be separated into two ‘-e’ parameters, enabling easier scripting: $ seq 3 | sed -e '2i\' -e hello 1 hello 2 3 $ sed -e '2i\' -e "$VAR" ‘c TEXT’ Replaces the line(s) with TEXT. This is a GNU extension to the standard ‘c’ command - see below for details. Example: Replace the 2nd to 9th lines with the word ‘hello’: $ seq 10 | sed '2,9c hello' 1 hello 10 Leading whitespace after the ‘c’ command is ignored. The text to add is read until the end of the line. ‘c\’ ‘TEXT’ Delete the lines matching the address or address-range, and output the lines of text which follow this command. Example: Replace 2nd to 4th lines with the words ‘hello’ and ‘world’ (⊣ indicates printed output lines): $ seq 5 | sed '2,4c\ hello\ world' ⊣1 ⊣hello ⊣world ⊣5 If no addresses are given, each line is replaced. A new cycle is started after this command is done, since the pattern space will have been deleted. In the following example, the ‘c’ starts a new cycle and the substitution command is not performed on the replaced text: $ seq 3 | sed '2c\ hello s/./X/' ⊣X ⊣hello ⊣X As a GNU extension, the ‘c’ command and TEXT can be separated into two ‘-e’ parameters, enabling easier scripting: $ seq 3 | sed -e '2c\' -e hello 1 hello 3 $ sed -e '2c\' -e "$VAR" ‘=’ Print out the current input line number (with a trailing newline). $ printf '%s\n' aaa bbb ccc | sed = 1 aaa 2 bbb 3 ccc As a GNU extension, this command accepts two addresses. ‘l N’ Print the pattern space in an unambiguous form: non-printable characters (and the ‘\’ character) are printed in C-style escaped form; long lines are split, with a trailing ‘\’ character to indicate the split; the end of each line is marked with a ‘$’. N specifies the desired line-wrap length; a length of 0 (zero) means to never wrap long lines. If omitted, the default as specified on the command line is used. The N parameter is a GNU ‘sed’ extension. ‘r FILENAME’ Reads file FILENAME. Example: $ seq 3 | sed '2r/etc/hostname' 1 2 fencepost.gnu.org 3 Queue the contents of FILENAME to be read and inserted into the output stream at the end of the current cycle, or when the next input line is read. Note that if FILENAME cannot be read, it is treated as if it were an empty file, without any error indication. As a GNU ‘sed’ extension, the special value ‘/dev/stdin’ is supported for the file name, which reads the contents of the standard input. As a GNU extension, this command accepts two addresses. The file will then be reread and inserted on each of the addressed lines. As a GNU ‘sed’ extension, the ‘r’ command accepts a zero address, inserting a file _before_ the first line of the input *note Adding a header to multiple files::. ‘w FILENAME’ Write the pattern space to FILENAME. As a GNU ‘sed’ extension, two special values of FILENAME are supported: ‘/dev/stderr’, which writes the result to the standard error, and ‘/dev/stdout’, which writes to the standard output.(1) The file will be created (or truncated) before the first input line is read; all ‘w’ commands (including instances of the ‘w’ flag on successful ‘s’ commands) which refer to the same FILENAME are output without closing and reopening the file. ‘D’ If pattern space contains no newline, start a normal new cycle as if the ‘d’ command was issued. Otherwise, delete text in the pattern space up to the first newline, and restart cycle with the resultant pattern space, without reading a new line of input. ‘N’ Add a newline to the pattern space, then append the next line of input to the pattern space. If there is no more input then ‘sed’ exits without processing any more commands. When ‘-z’ is used, a zero byte (the ascii ‘NUL’ character) is added between the lines (instead of a new line). By default ‘sed’ does not terminate if there is no ’next’ input line. This is a GNU extension which can be disabled with ‘--posix’. *Note N command on the last line: N_command_last_line. ‘P’ Print out the portion of the pattern space up to the first newline. ‘h’ Replace the contents of the hold space with the contents of the pattern space. ‘H’ Append a newline to the contents of the hold space, and then append the contents of the pattern space to that of the hold space. ‘g’ Replace the contents of the pattern space with the contents of the hold space. ‘G’ Append a newline to the contents of the pattern space, and then append the contents of the hold space to that of the pattern space. ‘x’ Exchange the contents of the hold and pattern spaces. ---------- Footnotes ---------- (1) This is equivalent to ‘p’ unless the ‘-i’ option is being used.  File: sed.info, Node: Programming Commands, Next: Extended Commands, Prev: Other Commands, Up: sed scripts 3.6 Commands for ‘sed’ gurus ============================ In most cases, use of these commands indicates that you are probably better off programming in something like ‘awk’ or Perl. But occasionally one is committed to sticking with ‘sed’, and these commands can enable one to write quite convoluted scripts. ‘: LABEL’ [No addresses allowed.] Specify the location of LABEL for branch commands. In all other respects, a no-op. ‘b LABEL’ Unconditionally branch to LABEL. The LABEL may be omitted, in which case the next cycle is started. ‘t LABEL’ Branch to LABEL only if there has been a successful ‘s’ubstitution since the last input line was read or conditional branch was taken. The LABEL may be omitted, in which case the next cycle is started.  File: sed.info, Node: Extended Commands, Next: Multiple commands syntax, Prev: Programming Commands, Up: sed scripts 3.7 Commands Specific to GNU ‘sed’ ================================== These commands are specific to GNU ‘sed’, so you must use them with care and only when you are sure that hindering portability is not evil. They allow you to check for GNU ‘sed’ extensions or to do tasks that are required quite often, yet are unsupported by standard ‘sed’s. ‘e [COMMAND]’ This command allows one to pipe input from a shell command into pattern space. Without parameters, the ‘e’ command executes the command that is found in pattern space and replaces the pattern space with the output; a trailing newline is suppressed. If a parameter is specified, instead, the ‘e’ command interprets it as a command and sends its output to the output stream. The command can run across multiple lines, all but the last ending with a back-slash. In both cases, the results are undefined if the command to be executed contains a NUL character. Note that, unlike the ‘r’ command, the output of the command will be printed immediately; the ‘r’ command instead delays the output to the end of the current cycle. ‘F’ Print out the file name of the current input file (with a trailing newline). ‘Q [EXIT-CODE]’ This command accepts only one address. This command is the same as ‘q’, but will not print the contents of pattern space. Like ‘q’, it provides the ability to return an exit code to the caller. This command can be useful because the only alternative ways to accomplish this apparently trivial function are to use the ‘-n’ option (which can unnecessarily complicate your script) or resorting to the following snippet, which wastes time by reading the whole file without any visible effect: :eat $d Quit silently on the last line N Read another line, silently g Overwrite pattern space each time to save memory b eat ‘R FILENAME’ Queue a line of FILENAME to be read and inserted into the output stream at the end of the current cycle, or when the next input line is read. Note that if FILENAME cannot be read, or if its end is reached, no line is appended, without any error indication. As with the ‘r’ command, the special value ‘/dev/stdin’ is supported for the file name, which reads a line from the standard input. ‘T LABEL’ Branch to LABEL only if there have been no successful ‘s’ubstitutions since the last input line was read or conditional branch was taken. The LABEL may be omitted, in which case the next cycle is started. ‘v VERSION’ This command does nothing, but makes ‘sed’ fail if GNU ‘sed’ extensions are not supported, simply because other versions of ‘sed’ do not implement it. In addition, you can specify the version of ‘sed’ that your script requires, such as ‘4.0.5’. The default is ‘4.0’ because that is the first version that implemented this command. This command enables all GNU extensions even if ‘POSIXLY_CORRECT’ is set in the environment. ‘W FILENAME’ Write to the given filename the portion of the pattern space up to the first newline. Everything said under the ‘w’ command about file handling holds here too. ‘z’ This command empties the content of pattern space. It is usually the same as ‘s/.*//’, but is more efficient and works in the presence of invalid multibyte sequences in the input stream. POSIX mandates that such sequences are _not_ matched by ‘.’, so that there is no portable way to clear ‘sed’’s buffers in the middle of the script in most multibyte locales (including UTF-8 locales).  File: sed.info, Node: Multiple commands syntax, Prev: Extended Commands, Up: sed scripts 3.8 Multiple commands syntax ============================ There are several methods to specify multiple commands in a ‘sed’ program. Using newlines is most natural when running a sed script from a file (using the ‘-f’ option). On the command line, all ‘sed’ commands may be separated by newlines. Alternatively, you may specify each command as an argument to an ‘-e’ option: $ seq 6 | sed '1d 3d 5d' 2 4 6 $ seq 6 | sed -e 1d -e 3d -e 5d 2 4 6 A semicolon (‘;’) may be used to separate most simple commands: $ seq 6 | sed '1d;3d;5d' 2 4 6 The ‘{’,‘}’,‘b’,‘t’,‘T’,‘:’ commands can be separated with a semicolon (this is a non-portable GNU ‘sed’ extension). $ seq 4 | sed '{1d;3d}' 2 4 $ seq 6 | sed '{1d;3d};5d' 2 4 6 Labels used in ‘b’,‘t’,‘T’,‘:’ commands are read until a semicolon. Leading and trailing whitespace is ignored. In the examples below the label is ‘x’. The first example works with GNU ‘sed’. The second is a portable equivalent. For more information about branching and labels *note Branching and flow control::. $ seq 3 | sed '/1/b x ; s/^/=/ ; :x ; 3d' 1 =2 $ seq 3 | sed -e '/1/bx' -e 's/^/=/' -e ':x' -e '3d' 1 =2 3.8.1 Commands Requiring a newline ---------------------------------- The following commands cannot be separated by a semicolon and require a newline: ‘a’,‘c’,‘i’ (append/change/insert) All characters following ‘a’,‘c’,‘i’ commands are taken as the text to append/change/insert. Using a semicolon leads to undesirable results: $ seq 2 | sed '1aHello ; 2d' 1 Hello ; 2d 2 Separate the commands using ‘-e’ or a newline: $ seq 2 | sed -e 1aHello -e 2d 1 Hello $ seq 2 | sed '1aHello 2d' 1 Hello Note that specifying the text to add (‘Hello’) immediately after ‘a’,‘c’,‘i’ is itself a GNU ‘sed’ extension. A portable, POSIX-compliant alternative is: $ seq 2 | sed '1a\ Hello 2d' 1 Hello ‘#’ (comment) All characters following ‘#’ until the next newline are ignored. $ seq 3 | sed '# this is a comment ; 2d' 1 2 3 $ seq 3 | sed '# this is a comment 2d' 1 3 ‘r’,‘R’,‘w’,‘W’ (reading and writing files) The ‘r’,‘R’,‘w’,‘W’ commands parse the filename until end of the line. If whitespace, comments or semicolons are found, they will be included in the filename, leading to unexpected results: $ seq 2 | sed '1w hello.txt ; 2d' 1 2 $ ls -log total 4 -rw-rw-r-- 1 2 Jan 23 23:03 hello.txt ; 2d $ cat 'hello.txt ; 2d' 1 Note that ‘sed’ silently ignores read/write errors in ‘r’,‘R’,‘w’,‘W’ commands (such as missing files). In the following example, ‘sed’ tries to read a file named ‘‘hello.txt ; N’’. The file is missing, and the error is silently ignored: $ echo x | sed '1rhello.txt ; N' x ‘e’ (command execution) Any characters following the ‘e’ command until the end of the line will be sent to the shell. If whitespace, comments or semicolons are found, they will be included in the shell command, leading to unexpected results: $ echo a | sed '1e touch foo#bar' a $ ls -1 foo#bar $ echo a | sed '1e touch foo ; s/a/b/' sh: 1: s/a/b/: not found a ‘s///[we]’ (substitute with ‘e’ or ‘w’ flags) In a substitution command, the ‘w’ flag writes the substitution result to a file, and the ‘e’ flag executes the substitution result as a shell command. As with the ‘r/R/w/W/e’ commands, these must be terminated with a newline. If whitespace, comments or semicolons are found, they will be included in the shell command or filename, leading to unexpected results: $ echo a | sed 's/a/b/w1.txt#foo' b $ ls -1 1.txt#foo  File: sed.info, Node: sed addresses, Next: sed regular expressions, Prev: sed scripts, Up: Top 4 Addresses: selecting lines **************************** * Menu: * Addresses overview:: Addresses overview * Numeric Addresses:: selecting lines by numbers * Regexp Addresses:: selecting lines by text matching * Range Addresses:: selecting a range of lines * Zero Address:: Using address ‘0’  File: sed.info, Node: Addresses overview, Next: Numeric Addresses, Up: sed addresses 4.1 Addresses overview ====================== Addresses determine on which line(s) the ‘sed’ command will be executed. The following command replaces any first occurrence of ‘hello’ with ‘world’ only on line 144: sed '144s/hello/world/' input.txt > output.txt If no address is specified, the command is performed on all lines. The following command replaces ‘hello’ with ‘world’, targeting every line of the input file. However, note that it modifies only the first instance of ‘hello’ on each line. Use the ‘g’ modifier to affect every instance on each affected line. sed 's/hello/world/' input.txt > output.txt Addresses can contain regular expressions to match lines based on content instead of line numbers. The following command replaces ‘hello’ with ‘world’ only on lines containing the string ‘apple’: sed '/apple/s/hello/world/' input.txt > output.txt An address range is specified with two addresses separated by a comma (‘,’). Addresses can be numeric, regular expressions, or a mix of both. The following command replaces ‘hello’ with ‘world’ only on lines 4 to 17 (inclusive): sed '4,17s/hello/world/' input.txt > output.txt Appending the ‘!’ character to the end of an address specification (before the command letter) negates the sense of the match. That is, if the ‘!’ character follows an address or an address range, then only lines which do _not_ match the addresses will be selected. The following command replaces ‘hello’ with ‘world’ only on lines _not_ containing the string ‘apple’: sed '/apple/!s/hello/world/' input.txt > output.txt The following command replaces ‘hello’ with ‘world’ only on lines 1 to 3 and from line 18 to the last line of the input file (i.e. excluding lines 4 to 17): sed '4,17!s/hello/world/' input.txt > output.txt  File: sed.info, Node: Numeric Addresses, Next: Regexp Addresses, Prev: Addresses overview, Up: sed addresses 4.2 Selecting lines by numbers ============================== Addresses in a ‘sed’ script can be in any of the following forms: ‘NUMBER’ Specifying a line number will match only that line in the input. (Note that ‘sed’ counts lines continuously across all input files unless ‘-i’ or ‘-s’ options are specified.) ‘$’ This address matches the last line of the last file of input, or the last line of each file when the ‘-i’ or ‘-s’ options are specified. ‘FIRST~STEP’ This GNU extension matches every STEPth line starting with line FIRST. In particular, lines will be selected when there exists a non-negative N such that the current line-number equals FIRST + (N * STEP). Thus, one would use ‘1~2’ to select the odd-numbered lines and ‘0~2’ for even-numbered lines; to pick every third line starting with the second, ‘2~3’ would be used; to pick every fifth line starting with the tenth, use ‘10~5’; and ‘50~0’ is just an obscure way of saying ‘50’. The following commands demonstrate the step address usage: $ seq 10 | sed -n '0~4p' 4 8 $ seq 10 | sed -n '1~3p' 1 4 7 10  File: sed.info, Node: Regexp Addresses, Next: Range Addresses, Prev: Numeric Addresses, Up: sed addresses 4.3 selecting lines by text matching ==================================== GNU ‘sed’ supports the following regular expression addresses. The default regular expression is *note Basic Regular Expression (BRE): BRE syntax. If ‘-E’ or ‘-r’ options are used, The regular expression should be in *note Extended Regular Expression (ERE): ERE syntax. syntax. *Note BRE vs ERE::. ‘/REGEXP/’ This will select any line which matches the regular expression REGEXP. If REGEXP itself includes any ‘/’ characters, each must be escaped by a backslash (‘\’). The following command prints lines in ‘/etc/passwd’ which end with ‘bash’(1): sed -n '/bash$/p' /etc/passwd The empty regular expression ‘//’ repeats the last regular expression match (the same holds if the empty regular expression is passed to the ‘s’ command). Note that modifiers to regular expressions are evaluated when the regular expression is compiled, thus it is invalid to specify them together with the empty regular expression. ‘\%REGEXP%’ (The ‘%’ may be replaced by any other single character.) This also matches the regular expression REGEXP, but allows one to use a different delimiter than ‘/’. This is particularly useful if the REGEXP itself contains a lot of slashes, since it avoids the tedious escaping of every ‘/’. If REGEXP itself includes any delimiter characters, each must be escaped by a backslash (‘\’). The following commands are equivalent. They print lines which start with ‘/home/alice/documents/’: sed -n '/^\/home\/alice\/documents\//p' sed -n '\%^/home/alice/documents/%p' sed -n '\;^/home/alice/documents/;p' ‘/REGEXP/I’ ‘\%REGEXP%I’ The ‘I’ modifier to regular-expression matching is a GNU extension which causes the REGEXP to be matched in a case-insensitive manner. In many other programming languages, a lower case ‘i’ is used for case-insensitive regular expression matching. However, in ‘sed’ the ‘i’ is used for the insert command (*note insert command::). Observe the difference between the following examples. In this example, ‘/b/I’ is the address: regular expression with ‘I’ modifier. ‘d’ is the delete command: $ printf "%s\n" a b c | sed '/b/Id' a c Here, ‘/b/’ is the address: a regular expression. ‘i’ is the insert command. ‘d’ is the value to insert. A line with ‘d’ is then inserted above the matched line: $ printf "%s\n" a b c | sed '/b/id' a d b c ‘/REGEXP/M’ ‘\%REGEXP%M’ The ‘M’ modifier to regular-expression matching is a GNU ‘sed’ extension which directs GNU ‘sed’ to match the regular expression in ‘multi-line’ mode. The modifier causes ‘^’ and ‘$’ to match respectively (in addition to the normal behavior) the empty string after a newline, and the empty string before a newline. There are special character sequences (‘\`’ and ‘\'’) which always match the beginning or the end of the buffer. In addition, the period character does not match a new-line character in multi-line mode. Regex addresses operate on the content of the current pattern space. If the pattern space is changed (for example with ‘s///’ command) the regular expression matching will operate on the changed text. In the following example, automatic printing is disabled with ‘-n’. The ‘s/2/X/’ command changes lines containing ‘2’ to ‘X’. The command ‘/[0-9]/p’ matches lines with digits and prints them. Because the second line is changed before the ‘/[0-9]/’ regex, it will not match and will not be printed: $ seq 3 | sed -n 's/2/X/ ; /[0-9]/p' 1 3 ---------- Footnotes ---------- (1) There are of course many other ways to do the same, e.g. grep 'bash$' /etc/passwd awk -F: '$7 == "/bin/bash"' /etc/passwd  File: sed.info, Node: Range Addresses, Next: Zero Address, Prev: Regexp Addresses, Up: sed addresses 4.4 Range Addresses =================== An address range can be specified by specifying two addresses separated by a comma (‘,’). An address range matches lines starting from where the first address matches, and continues until the second address matches (inclusively): $ seq 10 | sed -n '4,6p' 4 5 6 If the second address is a REGEXP, then checking for the ending match will start with the line _following_ the line which matched the first address: a range will always span at least two lines (except of course if the input stream ends). $ seq 10 | sed -n '4,/[0-9]/p' 4 5 If the second address is a NUMBER less than (or equal to) the line matching the first address, then only the one line is matched: $ seq 10 | sed -n '4,1p' 4 GNU ‘sed’ also supports some special two-address forms; all these are GNU extensions: ‘0,/REGEXP/’ A line number of ‘0’ can be used in an address specification like ‘0,/REGEXP/’ so that ‘sed’ will try to match REGEXP in the first input line too. In other words, ‘0,/REGEXP/’ is similar to ‘1,/REGEXP/’, except that if ADDR2 matches the very first line of input the ‘0,/REGEXP/’ form will consider it to end the range, whereas the ‘1,/REGEXP/’ form will match the beginning of its range and hence make the range span up to the _second_ occurrence of the regular expression. The following examples demonstrate the difference between starting with address 1 and 0: $ seq 10 | sed -n '1,/[0-9]/p' 1 2 $ seq 10 | sed -n '0,/[0-9]/p' 1 ‘ADDR1,+N’ Matches ADDR1 and the N lines following ADDR1. $ seq 10 | sed -n '6,+2p' 6 7 8 ADDR1 can be a line number or a regular expression. ‘ADDR1,~N’ Matches ADDR1 and the lines following ADDR1 until the next line whose input line number is a multiple of N. The following command prints starting at line 6, until the next line which is a multiple of 4 (i.e. line 8): $ seq 10 | sed -n '6,~4p' 6 7 8 ADDR1 can be a line number or a regular expression.  File: sed.info, Node: Zero Address, Prev: Range Addresses, Up: sed addresses 4.5 Zero Address ================ As a GNU ‘sed’ extension, ‘0’ address can be used in two cases: 1. In a regex range addresses as ‘0,/REGEXP/’ (*note Zero Address Regex Range::). 2. With the ‘r’ command, inserting a file before the first line (*note Adding a header to multiple files::). Note that these are the only places where the ‘0’ address makes sense; Commands which are given the ‘0’ address in any other way will give an error.  File: sed.info, Node: sed regular expressions, Next: advanced sed, Prev: sed addresses, Up: Top 5 Regular Expressions: selecting text ************************************* * Menu: * Regular Expressions Overview:: Overview of Regular expression in ‘sed’ * BRE vs ERE:: Basic (BRE) and extended (ERE) regular expression syntax * BRE syntax:: Overview of basic regular expression syntax * ERE syntax:: Overview of extended regular expression syntax * Character Classes and Bracket Expressions:: * regexp extensions:: Additional regular expression commands * Back-references and Subexpressions:: Back-references and Subexpressions * Escapes:: Specifying special characters * Locale Considerations:: Multibyte characters and locale considerations  File: sed.info, Node: Regular Expressions Overview, Next: BRE vs ERE, Up: sed regular expressions 5.1 Overview of regular expression in ‘sed’ =========================================== To know how to use ‘sed’, people should understand regular expressions (“regexp” for short). A regular expression is a pattern that is matched against a subject string from left to right. Most characters are “ordinary”: they stand for themselves in a pattern, and match the corresponding characters. Regular expressions in ‘sed’ are specified between two slashes. The following command prints lines containing the string ‘hello’: sed -n '/hello/p' The above example is equivalent to this ‘grep’ command: grep 'hello' The power of regular expressions comes from the ability to include alternatives and repetitions in the pattern. These are encoded in the pattern by the use of “special characters”, which do not stand for themselves but instead are interpreted in some special way. The character ‘^’ (caret) in a regular expression matches the beginning of the line. The character ‘.’ (dot) matches any single character. The following ‘sed’ command matches and prints lines which start with the letter ‘b’, followed by any single character, followed by the letter ‘d’: $ printf "%s\n" abode bad bed bit bid byte body | sed -n '/^b.d/p' bad bed bid body The following sections explain the meaning and usage of special characters in regular expressions.  File: sed.info, Node: BRE vs ERE, Next: BRE syntax, Prev: Regular Expressions Overview, Up: sed regular expressions 5.2 Basic (BRE) and extended (ERE) regular expression ===================================================== Basic and extended regular expressions are two variations on the syntax of the specified pattern. Basic Regular Expression (BRE) syntax is the default in ‘sed’ (and similarly in ‘grep’). Use the POSIX-specified ‘-E’ option (‘-r’, ‘--regexp-extended’) to enable Extended Regular Expression (ERE) syntax. In GNU ‘sed’, the only difference between basic and extended regular expressions is in the behavior of a few special characters: ‘?’, ‘+’, parentheses, braces (‘{}’), and ‘|’. With basic (BRE) syntax, these characters do not have special meaning unless prefixed with a backslash (‘\’); While with extended (ERE) syntax it is reversed: these characters are special unless they are prefixed with backslash (‘\’). Desired pattern Basic (BRE) Syntax Extended (ERE) Syntax -------------------------------------------------------------------------- literal ‘+’ (plus $ echo 'a+b=c' > foo $ echo 'a+b=c' > foo sign) $ sed -n '/a+b/p' foo $ sed -E -n '/a\+b/p' foo a+b=c a+b=c One or more ‘a’ $ echo aab > foo $ echo aab > foo characters $ sed -n '/a\+b/p' foo $ sed -E -n '/a+b/p' foo followed by ‘b’ aab aab (plus sign as special meta-character)  File: sed.info, Node: BRE syntax, Next: ERE syntax, Prev: BRE vs ERE, Up: sed regular expressions 5.3 Overview of basic regular expression syntax =============================================== Here is a brief description of regular expression syntax as used in ‘sed’. ‘CHAR’ A single ordinary character matches itself. ‘*’ Matches a sequence of zero or more instances of matches for the preceding regular expression, which must be an ordinary character, a special character preceded by ‘\’, a ‘.’, a grouped regexp (see below), or a bracket expression. As a GNU extension, a postfixed regular expression can also be followed by ‘*’; for example, ‘a**’ is equivalent to ‘a*’. POSIX 1003.1-2001 says that ‘*’ stands for itself when it appears at the start of a regular expression or subexpression, but many non-GNU implementations do not support this and portable scripts should instead use ‘\*’ in these contexts. ‘.’ Matches any character, including newline. ‘^’ Matches the null string at beginning of the pattern space, i.e. what appears after the circumflex must appear at the beginning of the pattern space. In most scripts, pattern space is initialized to the content of each line (*note How ‘sed’ works: Execution Cycle.). So, it is a useful simplification to think of ‘^#include’ as matching only lines where ‘#include’ is the first thing on the line—if there is any preceding space, for example, the match fails. This simplification is valid as long as the original content of pattern space is not modified, for example with an ‘s’ command. ‘^’ acts as a special character only at the beginning of the regular expression or subexpression (that is, after ‘\(’ or ‘\|’). Portable scripts should avoid ‘^’ at the beginning of a subexpression, though, as POSIX allows implementations that treat ‘^’ as an ordinary character in that context. ‘$’ It is the same as ‘^’, but refers to end of pattern space. ‘$’ also acts as a special character only at the end of the regular expression or subexpression (that is, before ‘\)’ or ‘\|’), and its use at the end of a subexpression is not portable. ‘[LIST]’ ‘[^LIST]’ Matches any single character in LIST: for example, ‘[aeiou]’ matches all vowels. A list may include sequences like ‘CHAR1-CHAR2’, which matches any character between (inclusive) CHAR1 and CHAR2. *Note Character Classes and Bracket Expressions::. ‘\+’ As ‘*’, but matches one or more. It is a GNU extension. ‘\?’ As ‘*’, but only matches zero or one. It is a GNU extension. ‘\{I\}’ As ‘*’, but matches exactly I sequences (I is a decimal integer; for portability, keep it between 0 and 255 inclusive). ‘\{I,J\}’ Matches between I and J, inclusive, sequences. ‘\{I,\}’ Matches more than or equal to I sequences. ‘\(REGEXP\)’ Groups the inner REGEXP as a whole, this is used to: • Apply postfix operators, like ‘\(abcd\)*’: this will search for zero or more whole sequences of ‘abcd’, while ‘abcd*’ would search for ‘abc’ followed by zero or more occurrences of ‘d’. Note that support for ‘\(abcd\)*’ is required by POSIX 1003.1-2001, but many non-GNU implementations do not support it and hence it is not universally portable. • Use back references (see below). ‘REGEXP1\|REGEXP2’ Matches either REGEXP1 or REGEXP2. Use parentheses to use complex alternative regular expressions. The matching process tries each alternative in turn, from left to right, and the first one that succeeds is used. It is a GNU extension. ‘REGEXP1REGEXP2’ Matches the concatenation of REGEXP1 and REGEXP2. Concatenation binds more tightly than ‘\|’, ‘^’, and ‘$’, but less tightly than the other regular expression operators. ‘\DIGIT’ Matches the DIGIT-th ‘\(...\)’ parenthesized subexpression in the regular expression. This is called a “back reference”. Subexpressions are implicitly numbered by counting occurrences of ‘\(’ left-to-right. ‘\n’ Matches the newline character. ‘\CHAR’ Matches CHAR, where CHAR is one of ‘$’, ‘*’, ‘.’, ‘[’, ‘\’, or ‘^’. Note that the only C-like backslash sequences that you can portably assume to be interpreted are ‘\n’ and ‘\\’; in particular ‘\t’ is not portable, and matches a ‘t’ under most implementations of ‘sed’, rather than a tab character. Note that the regular expression matcher is greedy, i.e., matches are attempted from left to right and, if two or more matches are possible starting at the same character, it selects the longest. Examples: ‘abcdef’ Matches ‘abcdef’. ‘a*b’ Matches zero or more ‘a’s followed by a single ‘b’. For example, ‘b’ or ‘aaaaab’. ‘a\?b’ Matches ‘b’ or ‘ab’. ‘a\+b\+’ Matches one or more ‘a’s followed by one or more ‘b’s: ‘ab’ is the shortest possible match, but other examples are ‘aaaab’ or ‘abbbbb’ or ‘aaaaaabbbbbbb’. ‘.*’ ‘.\+’ These two both match all the characters in a string; however, the first matches every string (including the empty string), while the second matches only strings containing at least one character. ‘^main.*(.*)’ This matches a string starting with ‘main’, followed by an opening and closing parenthesis. The ‘n’, ‘(’ and ‘)’ need not be adjacent. ‘^#’ This matches a string beginning with ‘#’. ‘\\$’ This matches a string ending with a single backslash. The regexp contains two backslashes for escaping. ‘\$’ Instead, this matches a string consisting of a single dollar sign, because it is escaped. ‘[a-zA-Z0-9]’ In the C locale, this matches any ASCII letters or digits. ‘[^ ‘’]\+’ (Here ‘’ stands for a single tab character.) This matches a string of one or more characters, none of which is a space or a tab. Usually this means a word. ‘^\(.*\)\n\1$’ This matches a string consisting of two equal substrings separated by a newline. ‘.\{9\}A$’ This matches nine characters followed by an ‘A’ at the end of a line. ‘^.\{15\}A’ This matches the start of a string that contains 16 characters, the last of which is an ‘A’.  File: sed.info, Node: ERE syntax, Next: Character Classes and Bracket Expressions, Prev: BRE syntax, Up: sed regular expressions 5.4 Overview of extended regular expression syntax ================================================== The only difference between basic and extended regular expressions is in the behavior of a few characters: ‘?’, ‘+’, parentheses, braces (‘{}’), and ‘|’. While basic regular expressions require these to be escaped if you want them to behave as special characters, when using extended regular expressions you must escape them if you want them _to match a literal character_. ‘|’ is special here because ‘\|’ is a GNU extension – standard basic regular expressions do not provide its functionality. Examples: ‘abc?’ becomes ‘abc\?’ when using extended regular expressions. It matches the literal string ‘abc?’. ‘c\+’ becomes ‘c+’ when using extended regular expressions. It matches one or more ‘c’s. ‘a\{3,\}’ becomes ‘a{3,}’ when using extended regular expressions. It matches three or more ‘a’s. ‘\(abc\)\{2,3\}’ becomes ‘(abc){2,3}’ when using extended regular expressions. It matches either ‘abcabc’ or ‘abcabcabc’. ‘\(abc*\)\1’ becomes ‘(abc*)\1’ when using extended regular expressions. Backreferences must still be escaped when using extended regular expressions. ‘a\|b’ becomes ‘a|b’ when using extended regular expressions. It matches ‘a’ or ‘b’.  File: sed.info, Node: Character Classes and Bracket Expressions, Next: regexp extensions, Prev: ERE syntax, Up: sed regular expressions 5.5 Character Classes and Bracket Expressions ============================================= A “bracket expression” is a list of characters enclosed by ‘[’ and ‘]’. It matches any single character in that list; if the first character of the list is the caret ‘^’, then it matches any character *not* in the list. For example, the following command replaces the strings ‘gray’ or ‘grey’ with ‘blue’: sed 's/gr[ae]y/blue/' Bracket expressions can be used in both *note basic: BRE syntax. and *note extended: ERE syntax. regular expressions (that is, with or without the ‘-E’/‘-r’ options). Within a bracket expression, a “range expression” consists of two characters separated by a hyphen. It matches any single character that sorts between the two characters, inclusive. In the default C locale, the sorting sequence is the native character order; for example, ‘[a-d]’ is equivalent to ‘[abcd]’. Finally, certain named classes of characters are predefined within bracket expressions, as follows. These named classes must be used _inside_ brackets themselves. Correct usage: $ echo 1 | sed 's/[[:digit:]]/X/' X Incorrect usage is rejected by newer ‘sed’ versions. Older versions accepted it but treated it as a single bracket expression (which is equivalent to ‘[dgit:]’, that is, only the characters D/G/I/T/:): # current GNU sed versions - incorrect usage rejected $ echo 1 | sed 's/[:digit:]/X/' sed: character class syntax is [[:space:]], not [:space:] # older GNU sed versions $ echo 1 | sed 's/[:digit:]/X/' 1 ‘[:alnum:]’ Alphanumeric characters: ‘[:alpha:]’ and ‘[:digit:]’; in the ‘C’ locale and ASCII character encoding, this is the same as ‘[0-9A-Za-z]’. ‘[:alpha:]’ Alphabetic characters: ‘[:lower:]’ and ‘[:upper:]’; in the ‘C’ locale and ASCII character encoding, this is the same as ‘[A-Za-z]’. ‘[:blank:]’ Blank characters: space and tab. ‘[:cntrl:]’ Control characters. In ASCII, these characters have octal codes 000 through 037, and 177 (DEL). In other character sets, these are the equivalent characters, if any. ‘[:digit:]’ Digits: ‘0 1 2 3 4 5 6 7 8 9’. ‘[:graph:]’ Graphical characters: ‘[:alnum:]’ and ‘[:punct:]’. ‘[:lower:]’ Lower-case letters; in the ‘C’ locale and ASCII character encoding, this is ‘a b c d e f g h i j k l m n o p q r s t u v w x y z’. ‘[:print:]’ Printable characters: ‘[:alnum:]’, ‘[:punct:]’, and space. ‘[:punct:]’ Punctuation characters; in the ‘C’ locale and ASCII character encoding, this is ‘! " # $ % & ' ( ) * + , - . / : ; < = > ? @ [ \ ] ^ _ ` { | } ~’. ‘[:space:]’ Space characters: in the ‘C’ locale, this is tab, newline, vertical tab, form feed, carriage return, and space. ‘[:upper:]’ Upper-case letters: in the ‘C’ locale and ASCII character encoding, this is ‘A B C D E F G H I J K L M N O P Q R S T U V W X Y Z’. ‘[:xdigit:]’ Hexadecimal digits: ‘0 1 2 3 4 5 6 7 8 9 A B C D E F a b c d e f’. Note that the brackets in these class names are part of the symbolic names, and must be included in addition to the brackets delimiting the bracket expression. Most meta-characters lose their special meaning inside bracket expressions: ‘]’ ends the bracket expression if it’s not the first list item. So, if you want to make the ‘]’ character a list item, you must put it first. ‘-’ represents the range if it’s not first or last in a list or the ending point of a range. ‘^’ represents the characters not in the list. If you want to make the ‘^’ character a list item, place it anywhere but first. TODO: incorporate this paragraph (copied verbatim from BRE section). The characters ‘$’, ‘*’, ‘.’, ‘[’, and ‘\’ are normally not special within LIST. For example, ‘[\*]’ matches either ‘\’ or ‘*’, because the ‘\’ is not special here. However, strings like ‘[.ch.]’, ‘[=a=]’, and ‘[:space:]’ are special within LIST and represent collating symbols, equivalence classes, and character classes, respectively, and ‘[’ is therefore special within LIST when it is followed by ‘.’, ‘=’, or ‘:’. Also, when not in ‘POSIXLY_CORRECT’ mode, special escapes like ‘\n’ and ‘\t’ are recognized within LIST. *Note Escapes::. ‘[.’ represents the open collating symbol. ‘.]’ represents the close collating symbol. ‘[=’ represents the open equivalence class. ‘=]’ represents the close equivalence class. ‘[:’ represents the open character class symbol, and should be followed by a valid character class name. ‘:]’ represents the close character class symbol.  File: sed.info, Node: regexp extensions, Next: Back-references and Subexpressions, Prev: Character Classes and Bracket Expressions, Up: sed regular expressions 5.6 regular expression extensions ================================= The following sequences have special meaning inside regular expressions (used in *note addresses: Regexp Addresses. and the ‘s’ command). These can be used in both *note basic: BRE syntax. and *note extended: ERE syntax. regular expressions (that is, with or without the ‘-E’/‘-r’ options). ‘\w’ Matches any “word” character. A “word” character is any letter or digit or the underscore character. $ echo "abc %-= def." | sed 's/\w/X/g' XXX %-= XXX. ‘\W’ Matches any “non-word” character. $ echo "abc %-= def." | sed 's/\W/X/g' abcXXXXXdefX ‘\b’ Matches a word boundary; that is it matches if the character to the left is a “word” character and the character to the right is a “non-word” character, or vice-versa. $ echo "abc %-= def." | sed 's/\b/X/g' XabcX %-= XdefX. ‘\B’ Matches everywhere but on a word boundary; that is it matches if the character to the left and the character to the right are either both “word” characters or both “non-word” characters. $ echo "abc %-= def." | sed 's/\B/X/g' aXbXc X%X-X=X dXeXf.X ‘\s’ Matches whitespace characters (spaces and tabs). Newlines embedded in the pattern/hold spaces will also match: $ echo "abc %-= def." | sed 's/\s/X/g' abcX%-=Xdef. ‘\S’ Matches non-whitespace characters. $ echo "abc %-= def." | sed 's/\S/X/g' XXX XXX XXXX ‘\<’ Matches the beginning of a word. $ echo "abc %-= def." | sed 's/\’ Matches the end of a word. $ echo "abc %-= def." | sed 's/\>/X/g' abcX %-= defX. ‘\`’ Matches only at the start of pattern space. This is different from ‘^’ in multi-line mode. Compare the following two examples: $ printf "a\nb\nc\n" | sed 'N;N;s/^/X/gm' Xa Xb Xc $ printf "a\nb\nc\n" | sed 'N;N;s/\`/X/gm' Xa b c ‘\'’ Matches only at the end of pattern space. This is different from ‘$’ in multi-line mode.  File: sed.info, Node: Back-references and Subexpressions, Next: Escapes, Prev: regexp extensions, Up: sed regular expressions 5.7 Back-references and Subexpressions ====================================== “back-references” are regular expression commands which refer to a previous part of the matched regular expression. Back-references are specified with backslash and a single digit (e.g. ‘\1’). The part of the regular expression they refer to is called a “subexpression”, and is designated with parentheses. Back-references and subexpressions are used in two cases: in the regular expression search pattern, and in the REPLACEMENT part of the ‘s’ command (*note Regular Expression Addresses: Regexp Addresses. and *note The "s" Command::). In a regular expression pattern, back-references are used to match the same content as a previously matched subexpression. In the following example, the subexpression is ‘.’ - any single character (being surrounded by parentheses makes it a subexpression). The back-reference ‘\1’ asks to match the same content (same character) as the sub-expression. The command below matches words starting with any character, followed by the letter ‘o’, followed by the same character as the first. $ sed -E -n '/^(.)o\1$/p' /usr/share/dict/words bob mom non pop sos tot wow Multiple subexpressions are automatically numbered from left-to-right. This command searches for 6-letter palindromes (the first three letters are 3 subexpressions, followed by 3 back-references in reverse order): $ sed -E -n '/^(.)(.)(.)\3\2\1$/p' /usr/share/dict/words redder In the ‘s’ command, back-references can be used in the REPLACEMENT part to refer back to subexpressions in the REGEXP part. The following example uses two subexpressions in the regular expression to match two space-separated words. The back-references in the REPLACEMENT part prints the words in a different order: $ echo "James Bond" | sed -E 's/(.*) (.*)/The name is \2, \1 \2./' The name is Bond, James Bond. When used with alternation, if the group does not participate in the match then the back-reference makes the whole match fail. For example, ‘a(.)|b\1’ will not match ‘ba’. When multiple regular expressions are given with ‘-e’ or from a file (‘-f FILE’), back-references are local to each expression.  File: sed.info, Node: Escapes, Next: Locale Considerations, Prev: Back-references and Subexpressions, Up: sed regular expressions 5.8 Escape Sequences - specifying special characters ==================================================== Until this chapter, we have only encountered escapes of the form ‘\^’, which tell ‘sed’ not to interpret the circumflex as a special character, but rather to take it literally. For example, ‘\*’ matches a single asterisk rather than zero or more backslashes. This chapter introduces another kind of escape(1)—that is, escapes that are applied to a character or sequence of characters that ordinarily are taken literally, and that ‘sed’ replaces with a special character. This provides a way of encoding non-printable characters in patterns in a visible manner. There is no restriction on the appearance of non-printing characters in a ‘sed’ script but when a script is being prepared in the shell or by text editing, it is usually easier to use one of the following escape sequences than the binary character it represents: The list of these escapes is: ‘\a’ Produces or matches a BEL character, that is an “alert” (ASCII 7). ‘\f’ Produces or matches a form feed (ASCII 12). ‘\n’ Produces or matches a newline (ASCII 10). ‘\r’ Produces or matches a carriage return (ASCII 13). ‘\t’ Produces or matches a horizontal tab (ASCII 9). ‘\v’ Produces or matches a so called “vertical tab” (ASCII 11). ‘\cX’ Produces or matches ‘CONTROL-X’, where X is any character. The precise effect of ‘\cX’ is as follows: if X is a lower case letter, it is converted to upper case. Then bit 6 of the character (hex 40) is inverted. Thus ‘\cz’ becomes hex 1A, but ‘\c{’ becomes hex 3B, while ‘\c;’ becomes hex 7B. ‘\dXXX’ Produces or matches a character whose decimal ASCII value is XXX. ‘\oXXX’ Produces or matches a character whose octal ASCII value is XXX. ‘\xXX’ Produces or matches a character whose hexadecimal ASCII value is XX. ‘\b’ (backspace) was omitted because of the conflict with the existing “word boundary” meaning. 5.8.1 Escaping Precedence ------------------------- GNU ‘sed’ processes escape sequences _before_ passing the text onto the regular-expression matching of the ‘s///’ command and Address matching. Thus the following two commands are equivalent (‘0x5e’ is the hexadecimal ASCII value of the character ‘^’): $ echo 'a^c' | sed 's/^/b/' ba^c $ echo 'a^c' | sed 's/\x5e/b/' ba^c As are the following (‘0x5b’,‘0x5d’ are the hexadecimal ASCII values of ‘[’,‘]’, respectively): $ echo abc | sed 's/[a]/x/' Xbc $ echo abc | sed 's/\x5ba\x5d/x/' Xbc However it is recommended to avoid such special characters due to unexpected edge-cases. For example, the following are not equivalent: $ echo 'a^c' | sed 's/\^/b/' abc $ echo 'a^c' | sed 's/\\\x5e/b/' a^c ---------- Footnotes ---------- (1) All the escapes introduced here are GNU extensions, with the exception of ‘\n’. In basic regular expression mode, setting ‘POSIXLY_CORRECT’ disables them inside bracket expressions.  File: sed.info, Node: Locale Considerations, Prev: Escapes, Up: sed regular expressions 5.9 Multibyte characters and Locale Considerations ================================================== GNU ‘sed’ processes valid multibyte characters in multibyte locales (e.g. ‘UTF-8’). (1) The following example uses the Greek letter Capital Sigma (Σ, Unicode code point ‘0x03A3’). In a ‘UTF-8’ locale, ‘sed’ correctly processes the Sigma as one character despite it being 2 octets (bytes): $ locale | grep LANG LANG=en_US.UTF-8 $ printf 'a\u03A3b' aΣb $ printf 'a\u03A3b' | sed 's/./X/g' XXX $ printf 'a\u03A3b' | od -tx1 -An 61 ce a3 62 To force ‘sed’ to process octets separately, use the ‘C’ locale (also known as the ‘POSIX’ locale): $ printf 'a\u03A3b' | LC_ALL=C sed 's/./X/g' XXXX 5.9.1 Invalid multibyte characters ---------------------------------- ‘sed’’s regular expressions _do not_ match invalid multibyte sequences in a multibyte locale. In the following examples, the ascii value ‘0xCE’ is an incomplete multibyte character (shown here as �). The regular expression ‘.’ does not match it: $ printf 'a\xCEb\n' a�e $ printf 'a\xCEb\n' | sed 's/./X/g' X�X $ printf 'a\xCEc\n' | sed 's/./X/g' | od -tx1c -An 58 ce 58 0a X X \n Similarly, the ’catch-all’ regular expression ‘.*’ does not match the entire line: $ printf 'a\xCEc\n' | sed 's/.*//' | od -tx1c -An ce 63 0a c \n GNU ‘sed’ offers the special ‘z’ command to clear the current pattern space regardless of invalid multibyte characters (i.e. it works like ‘s/.*//’ but also removes invalid multibyte characters): $ printf 'a\xCEc\n' | sed 'z' | od -tx1c -An 0a \n Alternatively, force the ‘C’ locale to process each octet separately (every octet is a valid character in the ‘C’ locale): $ printf 'a\xCEc\n' | LC_ALL=C sed 's/.*//' | od -tx1c -An 0a \n ‘sed’’s inability to process invalid multibyte characters can be used to detect such invalid sequences in a file. In the following examples, the ‘\xCE\xCE’ is an invalid multibyte sequence, while ‘\xCE\A3’ is a valid multibyte sequence (of the Greek Sigma character). The following ‘sed’ program removes all valid characters using ‘s/.//g’. Any content left in the pattern space (the invalid characters) are added to the hold space using the ‘H’ command. On the last line (‘$’), the hold space is retrieved (‘x’), newlines are removed (‘s/\n//g’), and any remaining octets are printed unambiguously (‘l’). Thus, any invalid multibyte sequences are printed as octal values: $ printf 'ab\nc\n\xCE\xCEde\n\xCE\xA3f\n' > invalid.txt $ cat invalid.txt ab c ��de Σf $ sed -n 's/.//g ; H ; ${x;s/\n//g;l}' invalid.txt \316\316$ With a few more commands, ‘sed’ can print the exact line number corresponding to each invalid characters (line 3). These characters can then be removed by forcing the ‘C’ locale and using octal escape sequences: $ sed -n 's/.//g;=;l' invalid.txt | paste - - | awk '$2!="$"' 3 \316\316$ $ LC_ALL=C sed '3s/\o316\o316//' invalid.txt > fixed.txt 5.9.2 Upper/Lower case conversion --------------------------------- GNU ‘sed’’s substitute command (‘s’) supports upper/lower case conversions using ‘\U’,‘\L’ codes. These conversions support multibyte characters: $ printf 'ABC\u03a3\n' ABCΣ $ printf 'ABC\u03a3\n' | sed 's/.*/\L&/' abcσ *Note The "s" Command::. 5.9.3 Multibyte regexp character classes ---------------------------------------- In other locales, the sorting sequence is not specified, and ‘[a-d]’ might be equivalent to ‘[abcd]’ or to ‘[aBbCcDd]’, or it might fail to match any character, or the set of characters that it matches might even be erratic. To obtain the traditional interpretation of bracket expressions, you can use the ‘C’ locale by setting the ‘LC_ALL’ environment variable to the value ‘C’. # TODO: is there any real-world system/locale where 'A' # is replaced by '-' ? $ echo A | sed 's/[a-z]/-/' A Their interpretation depends on the ‘LC_CTYPE’ locale; for example, ‘[[:alnum:]]’ means the character class of numbers and letters in the current locale. TODO: show example of collation # TODO: this works on glibc systems, not on musl-libc/freebsd/macosx. $ printf 'cliché\n' | LC_ALL=fr_FR.utf8 sed 's/[[=e=]]/X/g' clichX ---------- Footnotes ---------- (1) Some regexp edge-cases depends on the operating system and libc implementation. The examples shown are known to work as-expected on GNU/Linux systems using glibc.  File: sed.info, Node: advanced sed, Next: Examples, Prev: sed regular expressions, Up: Top 6 Advanced ‘sed’: cycles and buffers ************************************ * Menu: * Execution Cycle:: How ‘sed’ works * Hold and Pattern Buffers:: * Multiline techniques:: Using D,G,H,N,P to process multiple lines * Branching and flow control::  File: sed.info, Node: Execution Cycle, Next: Hold and Pattern Buffers, Up: advanced sed 6.1 How ‘sed’ Works =================== ‘sed’ maintains two data buffers: the active _pattern_ space, and the auxiliary _hold_ space. Both are initially empty. ‘sed’ operates by performing the following cycle on each line of input: first, ‘sed’ reads one line from the input stream, removes any trailing newline, and places it in the pattern space. Then commands are executed; each command can have an address associated to it: addresses are a kind of condition code, and a command is only executed if the condition is verified before the command is to be executed. When the end of the script is reached, unless the ‘-n’ option is in use, the contents of pattern space are printed out to the output stream, adding back the trailing newline if it was removed.(1) Then the next cycle starts for the next input line. Unless special commands (like ‘D’) are used, the pattern space is deleted between two cycles. The hold space, on the other hand, keeps its data between cycles (see commands ‘h’, ‘H’, ‘x’, ‘g’, ‘G’ to move data between both buffers). ---------- Footnotes ---------- (1) Actually, if ‘sed’ prints a line without the terminating newline, it will nevertheless print the missing newline as soon as more text is sent to the same output stream, which gives the “least expected surprise” even though it does not make commands like ‘sed -n p’ exactly identical to ‘cat’.  File: sed.info, Node: Hold and Pattern Buffers, Next: Multiline techniques, Prev: Execution Cycle, Up: advanced sed 6.2 Hold and Pattern Buffers ============================ TODO  File: sed.info, Node: Multiline techniques, Next: Branching and flow control, Prev: Hold and Pattern Buffers, Up: advanced sed 6.3 Multiline techniques - using D,G,H,N,P to process multiple lines ==================================================================== Multiple lines can be processed as one buffer using the ‘D’,‘G’,‘H’,‘N’,‘P’. They are similar to their lowercase counterparts (‘d’,‘g’, ‘h’,‘n’,‘p’), except that these commands append or subtract data while respecting embedded newlines - allowing adding and removing lines from the pattern and hold spaces. They operate as follows: ‘D’ _deletes_ line from the pattern space until the first newline, and restarts the cycle. ‘G’ _appends_ line from the hold space to the pattern space, with a newline before it. ‘H’ _appends_ line from the pattern space to the hold space, with a newline before it. ‘N’ _appends_ line from the input file to the pattern space. ‘P’ _prints_ line from the pattern space until the first newline. The following example illustrates the operation of ‘N’ and ‘D’ commands: $ seq 6 | sed -n 'N;l;D' 1\n2$ 2\n3$ 3\n4$ 4\n5$ 5\n6$ 1. ‘sed’ starts by reading the first line into the pattern space (i.e. ‘1’). 2. At the beginning of every cycle, the ‘N’ command appends a newline and the next line to the pattern space (i.e. ‘1’, ‘\n’, ‘2’ in the first cycle). 3. The ‘l’ command prints the content of the pattern space unambiguously. 4. The ‘D’ command then removes the content of pattern space up to the first newline (leaving ‘2’ at the end of the first cycle). 5. At the next cycle the ‘N’ command appends a newline and the next input line to the pattern space (e.g. ‘2’, ‘\n’, ‘3’). A common technique to process blocks of text such as paragraphs (instead of line-by-line) is using the following construct: sed '/./{H;$!d} ; x ; s/REGEXP/REPLACEMENT/' 1. The first expression, ‘/./{H;$!d}’ operates on all non-empty lines, and adds the current line (in the pattern space) to the hold space. On all lines except the last, the pattern space is deleted and the cycle is restarted. 2. The other expressions ‘x’ and ‘s’ are executed only on empty lines (i.e. paragraph separators). The ‘x’ command fetches the accumulated lines from the hold space back to the pattern space. The ‘s///’ command then operates on all the text in the paragraph (including the embedded newlines). The following example demonstrates this technique: $ cat input.txt a a a aa aaa aaaa aaaa aa aaaa aaa aaa bbbb bbb bbb bb bb bbb bb bbbbbbbb bbb ccc ccc cccc cccc ccccc c cc cc cc cc $ sed '/./{H;$!d} ; x ; s/^/\nSTART-->/ ; s/$/\n<--END/' input.txt START--> a a a aa aaa aaaa aaaa aa aaaa aaa aaa <--END START--> bbbb bbb bbb bb bb bbb bb bbbbbbbb bbb <--END START--> ccc ccc cccc cccc ccccc c cc cc cc cc <--END For more annotated examples, *note Text search across multiple lines:: and *note Line length adjustment::.  File: sed.info, Node: Branching and flow control, Prev: Multiline techniques, Up: advanced sed 6.4 Branching and Flow Control ============================== The branching commands ‘b’, ‘t’, and ‘T’ enable changing the flow of ‘sed’ programs. By default, ‘sed’ reads an input line into the pattern buffer, then continues to processes all commands in order. Commands without addresses affect all lines. Commands with addresses affect only matching lines. *Note Execution Cycle:: and *note Addresses overview::. ‘sed’ does not support a typical ‘if/then’ construct. Instead, some commands can be used as conditionals or to change the default flow control: ‘d’ delete (clears) the current pattern space, and restart the program cycle without processing the rest of the commands and without printing the pattern space. ‘D’ delete the contents of the pattern space _up to the first newline_, and restart the program cycle without processing the rest of the commands and without printing the pattern space. ‘[addr]X’ ‘[addr]{ X ; X ; X }’ ‘/regexp/X’ ‘/regexp/{ X ; X ; X }’ Addresses and regular expressions can be used as an ‘if/then’ conditional: If [ADDR] matches the current pattern space, execute the command(s). For example: The command ‘/^#/d’ means: _if_ the current pattern matches the regular expression ‘^#’ (a line starting with a hash), _then_ execute the ‘d’ command: delete the line without printing it, and restart the program cycle immediately. ‘b’ branch unconditionally (that is: always jump to a label, skipping or repeating other commands, without restarting a new cycle). Combined with an address, the branch can be conditionally executed on matched lines. ‘t’ branch conditionally (that is: jump to a label) _only if_ a ‘s///’ command has succeeded since the last input line was read or another conditional branch was taken. ‘T’ similar but opposite to the ‘t’ command: branch only if there has been _no_ successful substitutions since the last input line was read. The following two ‘sed’ programs are equivalent. The first (contrived) example uses the ‘b’ command to skip the ‘s///’ command on lines containing ‘1’. The second example uses an address with negation (‘!’) to perform substitution only on desired lines. The ‘y///’ command is still executed on all lines: $ printf '%s\n' a1 a2 a3 | sed -E '/1/bx ; s/a/z/ ; :x ; y/123/456/' a4 z5 z6 $ printf '%s\n' a1 a2 a3 | sed -E '/1/!s/a/z/ ; y/123/456/' a4 z5 z6 6.4.1 Branching and Cycles -------------------------- The ‘b’,‘t’ and ‘T’ commands can be followed by a label (typically a single letter). Labels are defined with a colon followed by one or more letters (e.g. ‘:x’). If the label is omitted the branch commands restart the cycle. Note the difference between branching to a label and restarting the cycle: when a cycle is restarted, ‘sed’ first prints the current content of the pattern space, then reads the next input line into the pattern space; Jumping to a label (even if it is at the beginning of the program) does not print the pattern space and does not read the next input line. The following program is a no-op. The ‘b’ command (the only command in the program) does not have a label, and thus simply restarts the cycle. On each cycle, the pattern space is printed and the next input line is read: $ seq 3 | sed b 1 2 3 The following example is an infinite-loop - it doesn’t terminate and doesn’t print anything. The ‘b’ command jumps to the ‘x’ label, and a new cycle is never started: $ seq 3 | sed ':x ; bx' # The above command requires gnu sed (which supports additional # commands following a label, without a newline). A portable equivalent: # sed -e ':x' -e bx Branching is often complemented with the ‘n’ or ‘N’ commands: both commands read the next input line into the pattern space without waiting for the cycle to restart. Before reading the next input line, ‘n’ prints the current pattern space then empties it, while ‘N’ appends a newline and the next input line to the pattern space. Consider the following two examples: $ seq 3 | sed ':x ; n ; bx' 1 2 3 $ seq 3 | sed ':x ; N ; bx' 1 2 3 • Both examples do not inf-loop, despite never starting a new cycle. • In the first example, the ‘n’ commands first prints the content of the pattern space, empties the pattern space then reads the next input line. • In the second example, the ‘N’ commands appends the next input line to the pattern space (with a newline). Lines are accumulated in the pattern space until there are no more input lines to read, then the ‘N’ command terminates the ‘sed’ program. When the program terminates, the end-of-cycle actions are performed, and the entire pattern space is printed. • The second example requires GNU ‘sed’, because it uses the non-POSIX-standard behavior of ‘N’. See the “‘N’ command on the last line” paragraph in *note Reporting Bugs::. • To further examine the difference between the two examples, try the following commands: printf '%s\n' aa bb cc dd | sed ':x ; n ; = ; bx' printf '%s\n' aa bb cc dd | sed ':x ; N ; = ; bx' printf '%s\n' aa bb cc dd | sed ':x ; n ; s/\n/***/ ; bx' printf '%s\n' aa bb cc dd | sed ':x ; N ; s/\n/***/ ; bx' 6.4.2 Branching example: joining lines -------------------------------------- As a real-world example of using branching, consider the case of quoted-printable (https://en.wikipedia.org/wiki/Quoted-printable) files, typically used to encode email messages. In these files long lines are split and marked with a “soft line break” consisting of a single ‘=’ character at the end of the line: $ cat jaques.txt All the wor= ld's a stag= e, And all the= men and wo= men merely = players: They have t= heir exits = and their e= ntrances; And one man= in his tim= e plays man= y parts. The following program uses an address match ‘/=$/’ as a conditional: If the current pattern space ends with a ‘=’, it reads the next input line using ‘N’, replaces all ‘=’ characters which are followed by a newline, and unconditionally branches (‘b’) to the beginning of the program without restarting a new cycle. If the pattern space does not ends with ‘=’, the default action is performed: the pattern space is printed and a new cycle is started: $ sed ':x ; /=$/ { N ; s/=\n//g ; bx }' jaques.txt All the world's a stage, And all the men and women merely players: They have their exits and their entrances; And one man in his time plays many parts. Here’s an alternative program with a slightly different approach: On all lines except the last, ‘N’ appends the line to the pattern space. A substitution command then removes soft line breaks (‘=’ at the end of a line, i.e. followed by a newline) by replacing them with an empty string. _if_ the substitution was successful (meaning the pattern space contained a line which should be joined), The conditional branch command ‘t’ jumps to the beginning of the program without completing or restarting the cycle. If the substitution failed (meaning there were no soft line breaks), The ‘t’ command will _not_ branch. Then, ‘P’ will print the pattern space content until the first newline, and ‘D’ will delete the pattern space content until the first new line. (To learn more about ‘N’, ‘P’ and ‘D’ commands *note Multiline techniques::). $ sed ':x ; $!N ; s/=\n// ; tx ; P ; D' jaques.txt All the world's a stage, And all the men and women merely players: They have their exits and their entrances; And one man in his time plays many parts. For more line-joining examples *note Joining lines::.  File: sed.info, Node: Examples, Next: Limitations, Prev: advanced sed, Up: Top 7 Some Sample Scripts ********************* Here are some ‘sed’ scripts to guide you in the art of mastering ‘sed’. * Menu: Useful one-liners: * Joining lines:: Some exotic examples: * Centering lines:: * Increment a number:: * Rename files to lower case:: * Print bash environment:: * Reverse chars of lines:: * Text search across multiple lines:: * Line length adjustment:: * Adding a header to multiple files:: Emulating standard utilities: * tac:: Reverse lines of files * cat -n:: Numbering lines * cat -b:: Numbering non-blank lines * wc -c:: Counting chars * wc -w:: Counting words * wc -l:: Counting lines * head:: Printing the first lines * tail:: Printing the last lines * uniq:: Make duplicate lines unique * uniq -d:: Print duplicated lines of input * uniq -u:: Remove all duplicated lines * cat -s:: Squeezing blank lines  File: sed.info, Node: Joining lines, Next: Centering lines, Up: Examples 7.1 Joining lines ================= This section uses ‘N’, ‘D’ and ‘P’ commands to process multiple lines, and the ‘b’ and ‘t’ commands for branching. *Note Multiline techniques:: and *note Branching and flow control::. Join specific lines (e.g. if lines 2 and 3 need to be joined): $ cat lines.txt hello hel lo hello $ sed '2{N;s/\n//;}' lines.txt hello hello hello Join backslash-continued lines: $ cat 1.txt this \ is \ a \ long \ line and another \ line $ sed -e ':x /\\$/ { N; s/\\\n//g ; bx }' 1.txt this is a long line and another line #TODO: The above requires gnu sed. # non-gnu seds need newlines after ':' and 'b' Join lines that start with whitespace (e.g SMTP headers): $ cat 2.txt Subject: Hello World Content-Type: multipart/alternative; boundary=94eb2c190cc6370f06054535da6a Date: Tue, 3 Jan 2017 19:41:16 +0000 (GMT) Authentication-Results: mx.gnu.org; dkim=pass header.i=@gnu.org; spf=pass Message-ID: From: John Doe To: Jane Smith $ sed -E ':a ; $!N ; s/\n\s+/ / ; ta ; P ; D' 2.txt Subject: Hello World Content-Type: multipart/alternative; boundary=94eb2c190cc6370f06054535da6a Date: Tue, 3 Jan 2017 19:41:16 +0000 (GMT) Authentication-Results: mx.gnu.org; dkim=pass header.i=@gnu.org; spf=pass Message-ID: From: John Doe To: Jane Smith # A portable (non-gnu) variation: # sed -e :a -e '$!N;s/\n */ /;ta' -e 'P;D'  File: sed.info, Node: Centering lines, Next: Increment a number, Prev: Joining lines, Up: Examples 7.2 Centering Lines =================== This script centers all lines of a file on a 80 columns width. To change that width, the number in ‘\{...\}’ must be replaced, and the number of added spaces also must be changed. Note how the buffer commands are used to separate parts in the regular expressions to be matched—this is a common technique. #!/usr/bin/sed -f # Put 80 spaces in the buffer 1 { x s/^$/ / s/^.*$/&&&&&&&&/ x } # delete leading and trailing spaces y// / s/^ *// s/ *$// # add a newline and 80 spaces to end of line G # keep first 81 chars (80 + a newline) s/^\(.\{81\}\).*$/\1/ # \2 matches half of the spaces, which are moved to the beginning s/^\(.*\)\n\(.*\)\2/\2\1/  File: sed.info, Node: Increment a number, Next: Rename files to lower case, Prev: Centering lines, Up: Examples 7.3 Increment a Number ====================== This script is one of a few that demonstrate how to do arithmetic in ‘sed’. This is indeed possible,(1) but must be done manually. To increment one number you just add 1 to last digit, replacing it by the following digit. There is one exception: when the digit is a nine the previous digits must be also incremented until you don’t have a nine. This solution by Bruno Haible is very clever and smart because it uses a single buffer; if you don’t have this limitation, the algorithm used in *note Numbering lines: cat -n, is faster. It works by replacing trailing nines with an underscore, then using multiple ‘s’ commands to increment the last digit, and then again substituting underscores with zeros. #!/usr/bin/sed -f /[^0-9]/ d # replace all trailing 9s by _ (any other character except digits, could # be used) :d s/9\(_*\)$/_\1/ td # incr last digit only. The first line adds a most-significant # digit of 1 if we have to add a digit. s/^\(_*\)$/1\1/; tn s/8\(_*\)$/9\1/; tn s/7\(_*\)$/8\1/; tn s/6\(_*\)$/7\1/; tn s/5\(_*\)$/6\1/; tn s/4\(_*\)$/5\1/; tn s/3\(_*\)$/4\1/; tn s/2\(_*\)$/3\1/; tn s/1\(_*\)$/2\1/; tn s/0\(_*\)$/1\1/; tn :n y/_/0/ ---------- Footnotes ---------- (1) ‘sed’ guru Greg Ubben wrote an implementation of the ‘dc’ RPN calculator! It is distributed together with sed.  File: sed.info, Node: Rename files to lower case, Next: Print bash environment, Prev: Increment a number, Up: Examples 7.4 Rename Files to Lower Case ============================== This is a pretty strange use of ‘sed’. We transform text, and transform it to be shell commands, then just feed them to shell. Don’t worry, even worse hacks are done when using ‘sed’; I have seen a script converting the output of ‘date’ into a ‘bc’ program! The main body of this is the ‘sed’ script, which remaps the name from lower to upper (or vice-versa) and even checks out if the remapped name is the same as the original name. Note how the script is parameterized using shell variables and proper quoting. #! /bin/sh # rename files to lower/upper case... # # usage: # move-to-lower * # move-to-upper * # or # move-to-lower -R . # move-to-upper -R . # help() { cat << eof Usage: $0 [-n] [-r] [-h] files... -n do nothing, only see what would be done -R recursive (use find) -h this message files files to remap to lower case Examples: $0 -n * (see if everything is ok, then...) $0 * $0 -R . eof } apply_cmd='sh' finder='echo "$@" | tr " " "\n"' files_only= while : do case "$1" in -n) apply_cmd='cat' ;; -R) finder='find "$@" -type f';; -h) help ; exit 1 ;; *) break ;; esac shift done if [ -z "$1" ]; then echo Usage: $0 [-h] [-n] [-r] files... exit 1 fi LOWER='abcdefghijklmnopqrstuvwxyz' UPPER='ABCDEFGHIJKLMNOPQRSTUVWXYZ' case `basename $0` in *upper*) TO=$UPPER; FROM=$LOWER ;; *) FROM=$UPPER; TO=$LOWER ;; esac eval $finder | sed -n ' # remove all trailing slashes s/\/*$// # add ./ if there is no path, only a filename /\//! s/^/.\// # save path+filename h # remove path s/.*\/// # do conversion only on filename y/'$FROM'/'$TO'/ # now line contains original path+file, while # hold space contains the new filename x # add converted file name to line, which now contains # path/file-name\nconverted-file-name G # check if converted file name is equal to original file name, # if it is, do not print anything /^.*\/\(.*\)\n\1/b # escape special characters for the shell s/["$`\\]/\\&/g # now, transform path/fromfile\n, into # mv path/fromfile path/tofile and print it s/^\(.*\/\)\(.*\)\n\(.*\)$/mv "\1\2" "\1\3"/p ' | $apply_cmd  File: sed.info, Node: Print bash environment, Next: Reverse chars of lines, Prev: Rename files to lower case, Up: Examples 7.5 Print ‘bash’ Environment ============================ This script strips the definition of the shell functions from the output of the ‘set’ Bourne-shell command. #!/bin/sh set | sed -n ' :x # if no occurrence of "=()" print and load next line /=()/! { p; b; } / () $/! { p; b; } # possible start of functions section # save the line in case this is a var like FOO="() " h # if the next line has a brace, we quit because # nothing comes after functions n /^{/ q # print the old line x; p # work on the new line now x; bx '  File: sed.info, Node: Reverse chars of lines, Next: Text search across multiple lines, Prev: Print bash environment, Up: Examples 7.6 Reverse Characters of Lines =============================== This script can be used to reverse the position of characters in lines. The technique moves two characters at a time, hence it is faster than more intuitive implementations. Note the ‘tx’ command before the definition of the label. This is often needed to reset the flag that is tested by the ‘t’ command. Imaginative readers will find uses for this script. An example is reversing the output of ‘banner’.(1) #!/usr/bin/sed -f /../! b # Reverse a line. Begin embedding the line between two newlines s/^.*$/\ &\ / # Move first character at the end. The regexp matches until # there are zero or one characters between the markers tx :x s/\(\n.\)\(.*\)\(.\n\)/\3\2\1/ tx # Remove the newline markers s/\n//g ---------- Footnotes ---------- (1) This requires another script to pad the output of banner; for example #! /bin/sh banner -w $1 $2 $3 $4 | sed -e :a -e '/^.\{0,'$1'\}$/ { s/$/ /; ba; }' | ~/sedscripts/reverseline.sed  File: sed.info, Node: Text search across multiple lines, Next: Line length adjustment, Prev: Reverse chars of lines, Up: Examples 7.7 Text search across multiple lines ===================================== This section uses ‘N’ and ‘D’ commands to search for consecutive words spanning multiple lines. *Note Multiline techniques::. These examples deal with finding doubled occurrences of words in a document. Finding doubled words in a single line is easy using GNU ‘grep’ and similarly with GNU ‘sed’: $ cat two-cities-dup1.txt It was the best of times, it was the worst of times, it was the the age of wisdom, it was the age of foolishness, $ grep -E '\b(\w+)\s+\1\b' two-cities-dup1.txt it was the the age of wisdom, $ grep -n -E '\b(\w+)\s+\1\b' two-cities-dup1.txt 3:it was the the age of wisdom, $ sed -En '/\b(\w+)\s+\1\b/p' two-cities-dup1.txt it was the the age of wisdom, $ sed -En '/\b(\w+)\s+\1\b/{=;p}' two-cities-dup1.txt 3 it was the the age of wisdom, • The regular expression ‘\b\w+\s+’ searches for word-boundary (‘\b’), followed by one-or-more word-characters (‘\w+’), followed by whitespace (‘\s+’). *Note regexp extensions::. • Adding parentheses around the ‘(\w+)’ expression creates a subexpression. The regular expression pattern ‘(PATTERN)\s+\1’ defines a subexpression (in the parentheses) followed by a back-reference, separated by whitespace. A successful match means the PATTERN was repeated twice in succession. *Note Back-references and Subexpressions::. • The word-boundery expression (‘\b’) at both ends ensures partial words are not matched (e.g. ‘the then’ is not a desired match). • The ‘-E’ option enables extended regular expression syntax, alleviating the need to add backslashes before the parenthesis. *Note ERE syntax::. When the doubled word span two lines the above regular expression will not find them as ‘grep’ and ‘sed’ operate line-by-line. By using ‘N’ and ‘D’ commands, ‘sed’ can apply regular expressions on multiple lines (that is, multiple lines are stored in the pattern space, and the regular expression works on it): $ cat two-cities-dup2.txt It was the best of times, it was the worst of times, it was the the age of wisdom, it was the age of foolishness, $ sed -En '{N; /\b(\w+)\s+\1\b/{=;p} ; D}' two-cities-dup2.txt 3 worst of times, it was the the age of wisdom, • The ‘N’ command appends the next line to the pattern space (thus ensuring it contains two consecutive lines in every cycle). • The regular expression uses ‘\s+’ for word separator which matches both spaces and newlines. • The regular expression matches, the entire pattern space is printed with ‘p’. No lines are printed by default due to the ‘-n’ option. • The ‘D’ removes the first line from the pattern space (up until the first newline), readying it for the next cycle. See the GNU ‘coreutils’ manual for an alternative solution using ‘tr -s’ and ‘uniq’ at .  File: sed.info, Node: Line length adjustment, Next: Adding a header to multiple files, Prev: Text search across multiple lines, Up: Examples 7.8 Line length adjustment ========================== This section uses ‘N’ and ‘P’ commands to read and write lines, and the ‘b’ command for branching. *Note Multiline techniques:: and *note Branching and flow control::. This (somewhat contrived) example deal with formatting and wrapping lines of text of the following input file: $ cat two-cities-mix.txt It was the best of times, it was the worst of times, it was the age of wisdom, it was the age of foolishness, The following sed program wraps lines at 40 characters: $ cat wrap40.sed # outer loop :x # Append a newline followed by the next input line to the pattern buffer N # Remove all newlines from the pattern buffer s/\n/ /g # Inner loop :y # Add a newline after the first 40 characters s/(.{40,40})/\1\n/ # If there is a newline in the pattern buffer # (i.e. the previous substitution added a newline) /\n/ { # There are newlines in the pattern buffer - # print the content until the first newline. P # Remove the printed characters and the first newline s/.*\n// # branch to label 'y' - repeat inner loop by } # No newlines in the pattern buffer - Branch to label 'x' (outer loop) # and read the next input line bx The wrapped output: $ sed -E -f wrap40.sed two-cities-mix.txt It was the best of times, it was the wor st of times, it was the age of wisdom, i t was the age of foolishness,  File: sed.info, Node: Adding a header to multiple files, Next: tac, Prev: Line length adjustment, Up: Examples 7.9 Adding a header to multiple files ===================================== GNU ‘sed’ can be used to safely modify multiple files at once. Add a single line to the beginning of source code files: sed -i '1i/* Copyright (C) FOO BAR */' *.c Adding a few lines is possible using ‘\n’ in the text: sed -i '1i/*\n * Copyright (C) FOO BAR\n * Created by Jane Doe\n */' *.c To add multiple lines from another file, use ‘0rFILE’. A typical use case is adding a license notice header to all files: ## Create the header file: $ cat<<'EOF'>LIC.TXT /* Copyright (C) 1989-2021 FOO BAR This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; If not, see . */ EOF ## Add the file at the beginning of all source code files: $ sed -i '0rLIC.TXT' *.cpp *.h With script files (e.g. ‘.sh’,‘.py’,‘.pl’ files) the license notice typically appears _after_ the first line (the ’shebang’ ‘#!’ line). The ‘1rFILE’ command will add ‘FILE’ _after_ the first line: ## Create the header file: $ cat<<'EOF'>LIC.TXT ## ## Copyright (C) 1989-2021 FOO BAR ## ## This program is free software; you can redistribute it and/or modify ## it under the terms of the GNU General Public License as published by ## the Free Software Foundation; either version 3, or (at your option) ## any later version. ## ## This program is distributed in the hope that it will be useful, ## but WITHOUT ANY WARRANTY; without even the implied warranty of ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the ## GNU General Public License for more details. ## ## You should have received a copy of the GNU General Public License ## along with this program; If not, see . ## ## EOF ## Add the file at the beginning of all source code files: $ sed -i '1rLIC.TXT' *.py *.sh The above ‘sed’ commands can be combined with ‘find’ to locate files in all subdirectories, ‘xargs’ to run additional commands on selected files and ‘grep’ to filter out files that already contain a copyright notice: find \( -iname '*.cpp' -o -iname '*.c' -o -iname '*.h' \) \ | xargs grep -Li copyright \ | xargs -r sed -i '0rLIC.TXT' Or a slightly safe version (handling files with spaces and newlines): find \( -iname '*.cpp' -o -iname '*.c' -o -iname '*.h' \) -print0 \ | xargs -0 grep -Z -Li copyright \ | xargs -0 -r sed -i '0rLIC.TXT' Note: using the ‘0’ address with ‘r’ command requires GNU ‘sed’ version 4.9 or later. *Note Zero Address::.  File: sed.info, Node: tac, Next: cat -n, Prev: Adding a header to multiple files, Up: Examples 7.10 Reverse Lines of Files =========================== This one begins a series of totally useless (yet interesting) scripts emulating various Unix commands. This, in particular, is a ‘tac’ workalike. Note that on implementations other than GNU ‘sed’ this script might easily overflow internal buffers. #!/usr/bin/sed -nf # reverse all lines of input, i.e. first line became last, ... # from the second line, the buffer (which contains all previous lines) # is *appended* to current line, so, the order will be reversed 1! G # on the last line we're done -- print everything $ p # store everything on the buffer again h  File: sed.info, Node: cat -n, Next: cat -b, Prev: tac, Up: Examples 7.11 Numbering Lines ==================== This script replaces ‘cat -n’; in fact it formats its output exactly like GNU ‘cat’ does. Of course this is completely useless and for two reasons: first, because somebody else did it in C, second, because the following Bourne-shell script could be used for the same purpose and would be much faster: #! /bin/sh sed -e "=" $@ | sed -e ' s/^/ / N s/^ *\(......\)\n/\1 / ' It uses ‘sed’ to print the line number, then groups lines two by two using ‘N’. Of course, this script does not teach as much as the one presented below. The algorithm used for incrementing uses both buffers, so the line is printed as soon as possible and then discarded. The number is split so that changing digits go in a buffer and unchanged ones go in the other; the changed digits are modified in a single step (using a ‘y’ command). The line number for the next line is then composed and stored in the hold space, to be used in the next iteration. #!/usr/bin/sed -nf # Prime the pump on the first line x /^$/ s/^.*$/1/ # Add the correct line number before the pattern G h # Format it and print it s/^/ / s/^ *\(......\)\n/\1 /p # Get the line number from hold space; add a zero # if we're going to add a digit on the next line g s/\n.*$// /^9*$/ s/^/0/ # separate changing/unchanged digits with an x s/.9*$/x&/ # keep changing digits in hold space h s/^.*x// y/0123456789/1234567890/ x # keep unchanged digits in pattern space s/x.*$// # compose the new number, remove the newline implicitly added by G G s/\n// h  File: sed.info, Node: cat -b, Next: wc -c, Prev: cat -n, Up: Examples 7.12 Numbering Non-blank Lines ============================== Emulating ‘cat -b’ is almost the same as ‘cat -n’—we only have to select which lines are to be numbered and which are not. The part that is common to this script and the previous one is not commented to show how important it is to comment ‘sed’ scripts properly... #!/usr/bin/sed -nf /^$/ { p b } # Same as cat -n from now x /^$/ s/^.*$/1/ G h s/^/ / s/^ *\(......\)\n/\1 /p x s/\n.*$// /^9*$/ s/^/0/ s/.9*$/x&/ h s/^.*x// y/0123456789/1234567890/ x s/x.*$// G s/\n// h  File: sed.info, Node: wc -c, Next: wc -w, Prev: cat -b, Up: Examples 7.13 Counting Characters ======================== This script shows another way to do arithmetic with ‘sed’. In this case we have to add possibly large numbers, so implementing this by successive increments would not be feasible (and possibly even more complicated to contrive than this script). The approach is to map numbers to letters, kind of an abacus implemented with ‘sed’. ‘a’s are units, ‘b’s are tens and so on: we simply add the number of characters on the current line as units, and then propagate the carry to tens, hundreds, and so on. As usual, running totals are kept in hold space. On the last line, we convert the abacus form back to decimal. For the sake of variety, this is done with a loop rather than with some 80 ‘s’ commands(1): first we convert units, removing ‘a’s from the number; then we rotate letters so that tens become ‘a’s, and so on until no more letters remain. #!/usr/bin/sed -nf # Add n+1 a's to hold space (+1 is for the newline) s/./a/g H x s/\n/a/ # Do the carry. The t's and b's are not necessary, # but they do speed up the thing t a : a; s/aaaaaaaaaa/b/g; t b; b done : b; s/bbbbbbbbbb/c/g; t c; b done : c; s/cccccccccc/d/g; t d; b done : d; s/dddddddddd/e/g; t e; b done : e; s/eeeeeeeeee/f/g; t f; b done : f; s/ffffffffff/g/g; t g; b done : g; s/gggggggggg/h/g; t h; b done : h; s/hhhhhhhhhh//g : done $! { h b } # On the last line, convert back to decimal : loop /a/! s/[b-h]*/&0/ s/aaaaaaaaa/9/ s/aaaaaaaa/8/ s/aaaaaaa/7/ s/aaaaaa/6/ s/aaaaa/5/ s/aaaa/4/ s/aaa/3/ s/aa/2/ s/a/1/ : next y/bcdefgh/abcdefg/ /[a-h]/ b loop p ---------- Footnotes ---------- (1) Some implementations have a limit of 199 commands per script  File: sed.info, Node: wc -w, Next: wc -l, Prev: wc -c, Up: Examples 7.14 Counting Words =================== This script is almost the same as the previous one, once each of the words on the line is converted to a single ‘a’ (in the previous script each letter was changed to an ‘a’). It is interesting that real ‘wc’ programs have optimized loops for ‘wc -c’, so they are much slower at counting words rather than characters. This script’s bottleneck, instead, is arithmetic, and hence the word-counting one is faster (it has to manage smaller numbers). Again, the common parts are not commented to show the importance of commenting ‘sed’ scripts. #!/usr/bin/sed -nf # Convert words to a's s/[ ][ ]*/ /g s/^/ / s/ [^ ][^ ]*/a /g s/ //g # Append them to hold space H x s/\n// # From here on it is the same as in wc -c. /aaaaaaaaaa/! bx; s/aaaaaaaaaa/b/g /bbbbbbbbbb/! bx; s/bbbbbbbbbb/c/g /cccccccccc/! bx; s/cccccccccc/d/g /dddddddddd/! bx; s/dddddddddd/e/g /eeeeeeeeee/! bx; s/eeeeeeeeee/f/g /ffffffffff/! bx; s/ffffffffff/g/g /gggggggggg/! bx; s/gggggggggg/h/g s/hhhhhhhhhh//g :x $! { h; b; } :y /a/! s/[b-h]*/&0/ s/aaaaaaaaa/9/ s/aaaaaaaa/8/ s/aaaaaaa/7/ s/aaaaaa/6/ s/aaaaa/5/ s/aaaa/4/ s/aaa/3/ s/aa/2/ s/a/1/ y/bcdefgh/abcdefg/ /[a-h]/ by p  File: sed.info, Node: wc -l, Next: head, Prev: wc -w, Up: Examples 7.15 Counting Lines =================== No strange things are done now, because ‘sed’ gives us ‘wc -l’ functionality for free!!! Look: #!/usr/bin/sed -nf $=  File: sed.info, Node: head, Next: tail, Prev: wc -l, Up: Examples 7.16 Printing the First Lines ============================= This script is probably the simplest useful ‘sed’ script. It displays the first 10 lines of input; the number of displayed lines is right before the ‘q’ command. #!/usr/bin/sed -f 10q  File: sed.info, Node: tail, Next: uniq, Prev: head, Up: Examples 7.17 Printing the Last Lines ============================ Printing the last N lines rather than the first is more complex but indeed possible. N is encoded in the second line, before the bang character. This script is similar to the ‘tac’ script in that it keeps the final output in the hold space and prints it at the end: #!/usr/bin/sed -nf 1! {; H; g; } 1,10 !s/[^\n]*\n// $p h Mainly, the scripts keeps a window of 10 lines and slides it by adding a line and deleting the oldest (the substitution command on the second line works like a ‘D’ command but does not restart the loop). The “sliding window” technique is a very powerful way to write efficient and complex ‘sed’ scripts, because commands like ‘P’ would require a lot of work if implemented manually. To introduce the technique, which is fully demonstrated in the rest of this chapter and is based on the ‘N’, ‘P’ and ‘D’ commands, here is an implementation of ‘tail’ using a simple “sliding window.” This looks complicated but in fact the working is the same as the last script: after we have kicked in the appropriate number of lines, however, we stop using the hold space to keep inter-line state, and instead use ‘N’ and ‘D’ to slide pattern space by one line: #!/usr/bin/sed -f 1h 2,10 {; H; g; } $q 1,9d N D Note how the first, second and fourth line are inactive after the first ten lines of input. After that, all the script does is: exiting on the last line of input, appending the next input line to pattern space, and removing the first line.  File: sed.info, Node: uniq, Next: uniq -d, Prev: tail, Up: Examples 7.18 Make Duplicate Lines Unique ================================ This is an example of the art of using the ‘N’, ‘P’ and ‘D’ commands, probably the most difficult to master. #!/usr/bin/sed -f h :b # On the last line, print and exit $b N /^\(.*\)\n\1$/ { # The two lines are identical. Undo the effect of # the n command. g bb } # If the N command had added the last line, print and exit $b # The lines are different; print the first and go # back working on the second. P D As you can see, we maintain a 2-line window using ‘P’ and ‘D’. This technique is often used in advanced ‘sed’ scripts.  File: sed.info, Node: uniq -d, Next: uniq -u, Prev: uniq, Up: Examples 7.19 Print Duplicated Lines of Input ==================================== This script prints only duplicated lines, like ‘uniq -d’. #!/usr/bin/sed -nf $b N /^\(.*\)\n\1$/ { # Print the first of the duplicated lines s/.*\n// p # Loop until we get a different line :b $b N /^\(.*\)\n\1$/ { s/.*\n// bb } } # The last line cannot be followed by duplicates $b # Found a different one. Leave it alone in the pattern space # and go back to the top, hunting its duplicates D  File: sed.info, Node: uniq -u, Next: cat -s, Prev: uniq -d, Up: Examples 7.20 Remove All Duplicated Lines ================================ This script prints only unique lines, like ‘uniq -u’. #!/usr/bin/sed -f # Search for a duplicate line --- until that, print what you find. $b N /^\(.*\)\n\1$/ ! { P D } :c # Got two equal lines in pattern space. At the # end of the file we simply exit $d # Else, we keep reading lines with N until we # find a different one s/.*\n// N /^\(.*\)\n\1$/ { bc } # Remove the last instance of the duplicate line # and go back to the top D  File: sed.info, Node: cat -s, Prev: uniq -u, Up: Examples 7.21 Squeezing Blank Lines ========================== As a final example, here are three scripts, of increasing complexity and speed, that implement the same function as ‘cat -s’, that is squeezing blank lines. The first leaves a blank line at the beginning and end if there are some already. #!/usr/bin/sed -f # on empty lines, join with next # Note there is a star in the regexp :x /^\n*$/ { N bx } # now, squeeze all '\n', this can be also done by: # s/^\(\n\)*/\1/ s/\n*/\ / This one is a bit more complex and removes all empty lines at the beginning. It does leave a single blank line at end if one was there. #!/usr/bin/sed -f # delete all leading empty lines 1,/^./{ /./!d } # on an empty line we remove it and all the following # empty lines, but one :x /./!{ N s/^\n$// tx } This removes leading and trailing blank lines. It is also the fastest. Note that loops are completely done with ‘n’ and ‘b’, without relying on ‘sed’ to restart the script automatically at the end of a line. #!/usr/bin/sed -nf # delete all (leading) blanks /./!d # get here: so there is a non empty :x # print it p # get next n # got chars? print it again, etc... /./bx # no, don't have chars: got an empty line :z # get next, if last line we finish here so no trailing # empty lines are written n # also empty? then ignore it, and get next... this will # remove ALL empty lines /./!bz # all empty lines were deleted/ignored, but we have a non empty. As # what we want to do is to squeeze, insert a blank line artificially i\ bx  File: sed.info, Node: Limitations, Next: Other Resources, Prev: Examples, Up: Top 8 GNU ‘sed’’s Limitations and Non-limitations ********************************************* For those who want to write portable ‘sed’ scripts, be aware that some implementations have been known to limit line lengths (for the pattern and hold spaces) to be no more than 4000 bytes. The POSIX standard specifies that conforming ‘sed’ implementations shall support at least 8192 byte line lengths. GNU ‘sed’ has no built-in limit on line length; as long as it can ‘malloc()’ more (virtual) memory, you can feed or construct lines as long as you like. However, recursion is used to handle subpatterns and indefinite repetition. This means that the available stack space may limit the size of the buffer that can be processed by certain patterns.  File: sed.info, Node: Other Resources, Next: Reporting Bugs, Prev: Limitations, Up: Top 9 Other Resources for Learning About ‘sed’ ****************************************** For up to date information about GNU ‘sed’ please visit . Send general questions and suggestions to . Visit the mailing list archives for past discussions at . The following resources provide information about ‘sed’ (both GNU ‘sed’ and other variations). Note these not maintained by GNU ‘sed’ developers. • sed ‘$HOME’: • sed FAQ: • seder’s grabbag: • The ‘sed-users’ mailing list maintained by Sven Guckes: (note this is _not_ the GNU ‘sed’ mailing list).  File: sed.info, Node: Reporting Bugs, Next: GNU Free Documentation License, Prev: Other Resources, Up: Top 10 Reporting Bugs ***************** Email bug reports to . Also, please include the output of ‘sed --version’ in the body of your report if at all possible. Please do not send a bug report like this: while building frobme-1.3.4 $ configure error→ sed: file sedscr line 1: Unknown option to 's' If GNU ‘sed’ doesn’t configure your favorite package, take a few extra minutes to identify the specific problem and make a stand-alone test case. Unlike other programs such as C compilers, making such test cases for ‘sed’ is quite simple. A stand-alone test case includes all the data necessary to perform the test, and the specific invocation of ‘sed’ that causes the problem. The smaller a stand-alone test case is, the better. A test case should not involve something as far removed from ‘sed’ as “try to configure frobme-1.3.4”. Yes, that is in principle enough information to look for the bug, but that is not a very practical prospect. Here are a few commonly reported bugs that are not bugs. ‘N’ command on the last line Most versions of ‘sed’ exit without printing anything when the ‘N’ command is issued on the last line of a file. GNU ‘sed’ prints pattern space before exiting unless of course the ‘-n’ command switch has been specified. This choice is by design. Default behavior (gnu extension, non-POSIX conforming): $ seq 3 | sed N 1 2 3 To force POSIX-conforming behavior: $ seq 3 | sed --posix N 1 2 For example, the behavior of sed N foo bar would depend on whether foo has an even or an odd number of lines(1). Or, when writing a script to read the next few lines following a pattern match, traditional implementations of ‘sed’ would force you to write something like /foo/{ $!N; $!N; $!N; $!N; $!N; $!N; $!N; $!N; $!N } instead of just /foo/{ N;N;N;N;N;N;N;N;N; } In any case, the simplest workaround is to use ‘$d;N’ in scripts that rely on the traditional behavior, or to set the ‘POSIXLY_CORRECT’ variable to a non-empty value. Regex syntax clashes (problems with backslashes) ‘sed’ uses the POSIX basic regular expression syntax. According to the standard, the meaning of some escape sequences is undefined in this syntax; notable in the case of ‘sed’ are ‘\|’, ‘\+’, ‘\?’, ‘\`’, ‘\'’, ‘\<’, ‘\>’, ‘\b’, ‘\B’, ‘\w’, and ‘\W’. As in all GNU programs that use POSIX basic regular expressions, ‘sed’ interprets these escape sequences as special characters. So, ‘x\+’ matches one or more occurrences of ‘x’. ‘abc\|def’ matches either ‘abc’ or ‘def’. This syntax may cause problems when running scripts written for other ‘sed’s. Some ‘sed’ programs have been written with the assumption that ‘\|’ and ‘\+’ match the literal characters ‘|’ and ‘+’. Such scripts must be modified by removing the spurious backslashes if they are to be used with modern implementations of ‘sed’, like GNU ‘sed’. On the other hand, some scripts use s|abc\|def||g to remove occurrences of _either_ ‘abc’ or ‘def’. While this worked until ‘sed’ 4.0.x, newer versions interpret this as removing the string ‘abc|def’. This is again undefined behavior according to POSIX, and this interpretation is arguably more robust: older ‘sed’s, for example, required that the regex matcher parsed ‘\/’ as ‘/’ in the common case of escaping a slash, which is again undefined behavior; the new behavior avoids this, and this is good because the regex matcher is only partially under our control. In addition, this version of ‘sed’ supports several escape characters (some of which are multi-character) to insert non-printable characters in scripts (‘\a’, ‘\c’, ‘\d’, ‘\o’, ‘\r’, ‘\t’, ‘\v’, ‘\x’). These can cause similar problems with scripts written for other ‘sed’s. ‘-i’ clobbers read-only files In short, ‘sed -i’ will let you delete the contents of a read-only file, and in general the ‘-i’ option (*note Invocation: Invoking sed.) lets you clobber protected files. This is not a bug, but rather a consequence of how the Unix file system works. The permissions on a file say what can happen to the data in that file, while the permissions on a directory say what can happen to the list of files in that directory. ‘sed -i’ will not ever open for writing a file that is already on disk. Rather, it will work on a temporary file that is finally renamed to the original name: if you rename or delete files, you’re actually modifying the contents of the directory, so the operation depends on the permissions of the directory, not of the file. For this same reason, ‘sed’ does not let you use ‘-i’ on a writable file in a read-only directory, and will break hard or symbolic links when ‘-i’ is used on such a file. ‘0a’ does not work (gives an error) There is no line 0. 0 is a special address that is only used to treat addresses like ‘0,/RE/’ as active when the script starts: if you write ‘1,/abc/d’ and the first line includes the string ‘abc’, then that match would be ignored because address ranges must span at least two lines (barring the end of the file); but what you probably wanted is to delete every line up to the first one including ‘abc’, and this is obtained with ‘0,/abc/d’. ‘[a-z]’ is case insensitive You are encountering problems with locales. POSIX mandates that ‘[a-z]’ uses the current locale’s collation order – in C parlance, that means using ‘strcoll(3)’ instead of ‘strcmp(3)’. Some locales have a case-insensitive collation order, others don’t. Another problem is that ‘[a-z]’ tries to use collation symbols. This only happens if you are on the GNU system, using GNU libc’s regular expression matcher instead of compiling the one supplied with GNU sed. In a Danish locale, for example, the regular expression ‘^[a-z]$’ matches the string ‘aa’, because this is a single collating symbol that comes after ‘a’ and before ‘b’; ‘ll’ behaves similarly in Spanish locales, or ‘ij’ in Dutch locales. To work around these problems, which may cause bugs in shell scripts, set the ‘LC_COLLATE’ and ‘LC_CTYPE’ environment variables to ‘C’. ‘s/.*//’ does not clear pattern space This happens if your input stream includes invalid multibyte sequences. POSIX mandates that such sequences are _not_ matched by ‘.’, so that ‘s/.*//’ will not clear pattern space as you would expect. In fact, there is no way to clear sed’s buffers in the middle of the script in most multibyte locales (including UTF-8 locales). For this reason, GNU ‘sed’ provides a ‘z’ command (for ‘zap’) as an extension. To work around these problems, which may cause bugs in shell scripts, set the ‘LC_COLLATE’ and ‘LC_CTYPE’ environment variables to ‘C’. ---------- Footnotes ---------- (1) which is the actual “bug” that prompted the change in behavior  File: sed.info, Node: GNU Free Documentation License, Next: Concept Index, Prev: Reporting Bugs, Up: Top Appendix A GNU Free Documentation License ***************************************** Version 1.3, 3 November 2008 Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. 0. PREAMBLE The purpose of this License is to make a manual, textbook, or other functional and useful document “free” in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. 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The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing. ADDENDUM: How to use this License for your documents ==================================================== To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page: Copyright (C) YEAR YOUR NAME. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled ``GNU Free Documentation License''. If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this: with the Invariant Sections being LIST THEIR TITLES, with the Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST. If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation. If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.  File: sed.info, Node: Concept Index, Next: Command and Option Index, Prev: GNU Free Documentation License, Up: Top Concept Index ************* This is a general index of all issues discussed in this manual, with the exception of the ‘sed’ commands and command-line options. [index] * Menu: * -e, example: Overview. (line 46) * -e, example <1>: sed script overview. (line 37) * –expression, example: Overview. (line 46) * -f, example: Overview. (line 46) * -f, example <1>: sed script overview. (line 37) * –file, example: Overview. (line 46) * -i, example: Overview. (line 26) * -n, example: Overview. (line 33) * -s, example: Overview. (line 40) * 0 address: Reporting Bugs. (line 114) * ;, command separator: sed script overview. (line 37) * a, and semicolons: sed script overview. (line 56) * Additional reading about sed: Other Resources. (line 13) * ADDR1,+N: Range Addresses. (line 31) * ADDR1,~N: Range Addresses. (line 31) * address range, example: sed script overview. (line 23) * Address, as a regular expression: Regexp Addresses. (line 13) * Address, last line: Numeric Addresses. (line 13) * Address, numeric: Numeric Addresses. (line 8) * addresses, excluding: Addresses overview. (line 33) * Addresses, in sed scripts: Numeric Addresses. (line 6) * addresses, negating: Addresses overview. (line 33) * addresses, numeric: Addresses overview. (line 6) * addresses, range: Addresses overview. (line 26) * addresses, regular expression: Addresses overview. (line 20) * addresses, syntax: sed script overview. (line 13) * alphabetic characters: Character Classes and Bracket Expressions. (line 49) * alphanumeric characters: Character Classes and Bracket Expressions. (line 44) * Append hold space to pattern space: Other Commands. (line 288) * Append next input line to pattern space: Other Commands. (line 261) * Append pattern space to hold space: Other Commands. (line 280) * Appending text after a line: Other Commands. (line 45) * b, joining lines with: Branching and flow control. (line 150) * b, versus t: Branching and flow control. (line 150) * back-reference: Back-references and Subexpressions. (line 6) * Backreferences, in regular expressions: The "s" Command. (line 18) * blank characters: Character Classes and Bracket Expressions. (line 54) * bracket expression: Character Classes and Bracket Expressions. (line 6) * Branch to a label, if s/// failed: Extended Commands. (line 63) * Branch to a label, if s/// succeeded: Programming Commands. (line 22) * Branch to a label, unconditionally: Programming Commands. (line 18) * branching and n, N: Branching and flow control. (line 105) * branching, infinite loop: Branching and flow control. (line 95) * branching, joining lines: Branching and flow control. (line 150) * Buffer spaces, pattern and hold: Execution Cycle. (line 6) * Bugs, reporting: Reporting Bugs. (line 6) * c, and semicolons: sed script overview. (line 56) * case insensitive, regular expression: Regexp Addresses. (line 47) * Case-insensitive matching: The "s" Command. (line 117) * Caveat — #n on first line: Common Commands. (line 20) * character class: Character Classes and Bracket Expressions. (line 6) * character classes: Character Classes and Bracket Expressions. (line 43) * classes of characters: Character Classes and Bracket Expressions. (line 43) * Command groups: Common Commands. (line 91) * Comments, in scripts: Common Commands. (line 12) * Conditional branch: Programming Commands. (line 22) * Conditional branch <1>: Extended Commands. (line 63) * control characters: Character Classes and Bracket Expressions. (line 57) * Copy hold space into pattern space: Other Commands. (line 284) * Copy pattern space into hold space: Other Commands. (line 276) * cycle, restarting: Branching and flow control. (line 75) * d, example: sed script overview. (line 23) * Delete first line from pattern space: Other Commands. (line 255) * digit characters: Character Classes and Bracket Expressions. (line 62) * Disabling autoprint, from command line: Command-Line Options. (line 23) * empty regular expression: Regexp Addresses. (line 22) * Emptying pattern space: Extended Commands. (line 85) * Emptying pattern space <1>: Reporting Bugs. (line 143) * Evaluate Bourne-shell commands: Extended Commands. (line 12) * Evaluate Bourne-shell commands, after substitution: The "s" Command. (line 108) * example, address range: sed script overview. (line 23) * example, regular expression: sed script overview. (line 28) * Exchange hold space with pattern space: Other Commands. (line 292) * Excluding lines: Addresses overview. (line 33) * exit status: Exit status. (line 6) * exit status, example: Exit status. (line 25) * Extended regular expressions, choosing: Command-Line Options. (line 135) * Extended regular expressions, syntax: ERE syntax. (line 6) * File name, printing: Extended Commands. (line 30) * Files to be processed as input: Command-Line Options. (line 181) * Flow of control in scripts: Programming Commands. (line 11) * Global substitution: The "s" Command. (line 74) * GNU extensions, /dev/stderr file: The "s" Command. (line 101) * GNU extensions, /dev/stderr file <1>: Other Commands. (line 244) * GNU extensions, /dev/stdin file: Other Commands. (line 227) * GNU extensions, /dev/stdin file <1>: Extended Commands. (line 53) * GNU extensions, /dev/stdout file: Command-Line Options. (line 189) * GNU extensions, /dev/stdout file <1>: The "s" Command. (line 101) * GNU extensions, /dev/stdout file <2>: Other Commands. (line 244) * GNU extensions, 0 address: Range Addresses. (line 31) * GNU extensions, 0 address <1>: Reporting Bugs. (line 114) * GNU extensions, 0,ADDR2 addressing: Range Addresses. (line 31) * GNU extensions, ADDR1,+N addressing: Range Addresses. (line 31) * GNU extensions, ADDR1,~N addressing: Range Addresses. (line 31) * GNU extensions, branch if s/// failed: Extended Commands. (line 63) * GNU extensions, case modifiers in s commands: The "s" Command. (line 29) * GNU extensions, checking for their presence: Extended Commands. (line 69) * GNU extensions, debug: Command-Line Options. (line 29) * GNU extensions, disabling: Command-Line Options. (line 102) * GNU extensions, emptying pattern space: Extended Commands. (line 85) * GNU extensions, emptying pattern space <1>: Reporting Bugs. (line 143) * GNU extensions, evaluating Bourne-shell commands: The "s" Command. (line 108) * GNU extensions, evaluating Bourne-shell commands <1>: Extended Commands. (line 12) * GNU extensions, extended regular expressions: Command-Line Options. (line 135) * GNU extensions, g and NUMBER modifier: The "s" Command. (line 80) * GNU extensions, I modifier: The "s" Command. (line 117) * GNU extensions, I modifier <1>: Regexp Addresses. (line 47) * GNU extensions, in-place editing: Command-Line Options. (line 56) * GNU extensions, in-place editing <1>: Reporting Bugs. (line 95) * GNU extensions, M modifier: The "s" Command. (line 122) * GNU extensions, M modifier <1>: Regexp Addresses. (line 75) * GNU extensions, modifiers and the empty regular expression: Regexp Addresses. (line 22) * GNU extensions, N~M addresses: Numeric Addresses. (line 18) * GNU extensions, quitting silently: Extended Commands. (line 36) * GNU extensions, R command: Extended Commands. (line 53) * GNU extensions, reading a file a line at a time: Extended Commands. (line 53) * GNU extensions, returning an exit code: Common Commands. (line 28) * GNU extensions, returning an exit code <1>: Extended Commands. (line 36) * GNU extensions, setting line length: Other Commands. (line 207) * GNU extensions, special escapes: Escapes. (line 6) * GNU extensions, special escapes <1>: Reporting Bugs. (line 88) * GNU extensions, special two-address forms: Range Addresses. (line 31) * GNU extensions, subprocesses: The "s" Command. (line 108) * GNU extensions, subprocesses <1>: Extended Commands. (line 12) * GNU extensions, to basic regular expressions: BRE syntax. (line 13) * GNU extensions, to basic regular expressions <1>: BRE syntax. (line 59) * GNU extensions, to basic regular expressions <2>: BRE syntax. (line 62) * GNU extensions, to basic regular expressions <3>: BRE syntax. (line 77) * GNU extensions, to basic regular expressions <4>: BRE syntax. (line 87) * GNU extensions, to basic regular expressions <5>: Reporting Bugs. (line 61) * GNU extensions, two addresses supported by most commands: Other Commands. (line 61) * GNU extensions, two addresses supported by most commands <1>: Other Commands. (line 115) * GNU extensions, two addresses supported by most commands <2>: Other Commands. (line 204) * GNU extensions, two addresses supported by most commands <3>: Other Commands. (line 236) * GNU extensions, unlimited line length: Limitations. (line 6) * GNU extensions, writing first line to a file: Extended Commands. (line 80) * Goto, in scripts: Programming Commands. (line 18) * graphic characters: Character Classes and Bracket Expressions. (line 65) * Greedy regular expression matching: BRE syntax. (line 113) * Grouping commands: Common Commands. (line 91) * hexadecimal digits: Character Classes and Bracket Expressions. (line 88) * Hold space, appending from pattern space: Other Commands. (line 280) * Hold space, appending to pattern space: Other Commands. (line 288) * Hold space, copy into pattern space: Other Commands. (line 284) * Hold space, copying pattern space into: Other Commands. (line 276) * Hold space, definition: Execution Cycle. (line 6) * Hold space, exchange with pattern space: Other Commands. (line 292) * i, and semicolons: sed script overview. (line 56) * In-place editing: Reporting Bugs. (line 95) * In-place editing, activating: Command-Line Options. (line 56) * In-place editing, Perl-style backup file names: Command-Line Options. (line 67) * infinite loop, branching: Branching and flow control. (line 95) * Inserting text before a line: Other Commands. (line 104) * joining lines with branching: Branching and flow control. (line 150) * joining quoted-printable lines: Branching and flow control. (line 150) * labels: Branching and flow control. (line 75) * Labels, in scripts: Programming Commands. (line 14) * Last line, selecting: Numeric Addresses. (line 13) * Line length, setting: Command-Line Options. (line 97) * Line length, setting <1>: Other Commands. (line 207) * Line number, printing: Other Commands. (line 194) * Line selection: Numeric Addresses. (line 6) * Line, selecting by number: Numeric Addresses. (line 8) * Line, selecting by regular expression match: Regexp Addresses. (line 13) * Line, selecting last: Numeric Addresses. (line 13) * List pattern space: Other Commands. (line 207) * lower-case letters: Character Classes and Bracket Expressions. (line 68) * Mixing g and NUMBER modifiers in the s command: The "s" Command. (line 80) * multiple files: Overview. (line 40) * multiple sed commands: sed script overview. (line 37) * n, and branching: Branching and flow control. (line 105) * N, and branching: Branching and flow control. (line 105) * named character classes: Character Classes and Bracket Expressions. (line 43) * newline, command separator: sed script overview. (line 37) * Next input line, append to pattern space: Other Commands. (line 261) * Next input line, replace pattern space with: Common Commands. (line 61) * Non-bugs, 0 address: Reporting Bugs. (line 114) * Non-bugs, in-place editing: Reporting Bugs. (line 95) * Non-bugs, localization-related: Reporting Bugs. (line 124) * Non-bugs, localization-related <1>: Reporting Bugs. (line 143) * Non-bugs, N command on the last line: Reporting Bugs. (line 30) * Non-bugs, regex syntax clashes: Reporting Bugs. (line 61) * numeric addresses: Addresses overview. (line 6) * numeric characters: Character Classes and Bracket Expressions. (line 62) * omitting labels: Branching and flow control. (line 75) * output: Overview. (line 26) * output, suppressing: Overview. (line 33) * p, example: Overview. (line 33) * paragraphs, processing: Multiline techniques. (line 53) * parameters, script: Overview. (line 46) * Parenthesized substrings: The "s" Command. (line 18) * Pattern space, definition: Execution Cycle. (line 6) * Portability, comments: Common Commands. (line 15) * Portability, line length limitations: Limitations. (line 6) * Portability, N command on the last line: Reporting Bugs. (line 30) * POSIXLY_CORRECT behavior, bracket expressions: Character Classes and Bracket Expressions. (line 112) * POSIXLY_CORRECT behavior, enabling: Command-Line Options. (line 105) * POSIXLY_CORRECT behavior, escapes: Escapes. (line 11) * POSIXLY_CORRECT behavior, N command: Reporting Bugs. (line 56) * Print first line from pattern space: Other Commands. (line 273) * printable characters: Character Classes and Bracket Expressions. (line 72) * Printing file name: Extended Commands. (line 30) * Printing line number: Other Commands. (line 194) * Printing text unambiguously: Other Commands. (line 207) * processing paragraphs: Multiline techniques. (line 53) * punctuation characters: Character Classes and Bracket Expressions. (line 75) * Q, example: Exit status. (line 25) * q, example: sed script overview. (line 28) * Quitting: Common Commands. (line 28) * Quitting <1>: Extended Commands. (line 36) * quoted-printable lines, joining: Branching and flow control. (line 150) * range addresses: Addresses overview. (line 26) * range expression: Character Classes and Bracket Expressions. (line 18) * Range of lines: Range Addresses. (line 6) * Range with start address of zero: Range Addresses. (line 31) * Read next input line: Common Commands. (line 61) * Read text from a file: Other Commands. (line 219) * Read text from a file <1>: Extended Commands. (line 53) * regex addresses and input lines: Regexp Addresses. (line 84) * regex addresses and pattern space: Regexp Addresses. (line 84) * regular expression addresses: Addresses overview. (line 20) * regular expression, example: sed script overview. (line 28) * Replace hold space with copy of pattern space: Other Commands. (line 276) * Replace pattern space with copy of hold space: Other Commands. (line 284) * Replacing all text matching regexp in a line: The "s" Command. (line 74) * Replacing only Nth match of regexp in a line: The "s" Command. (line 78) * Replacing selected lines with other text: Other Commands. (line 157) * Requiring GNU sed: Extended Commands. (line 69) * restarting a cycle: Branching and flow control. (line 75) * Sandbox mode: Command-Line Options. (line 157) * script parameter: Overview. (line 46) * Script structure: sed script overview. (line 6) * Script, from a file: Command-Line Options. (line 51) * Script, from command line: Command-Line Options. (line 46) * sed commands syntax: sed script overview. (line 13) * sed commands, multiple: sed script overview. (line 37) * sed script structure: sed script overview. (line 6) * Selecting lines to process: Numeric Addresses. (line 6) * Selecting non-matching lines: Addresses overview. (line 33) * semicolons, command separator: sed script overview. (line 37) * Several lines, selecting: Range Addresses. (line 6) * Slash character, in regular expressions: Regexp Addresses. (line 32) * space characters: Character Classes and Bracket Expressions. (line 80) * Spaces, pattern and hold: Execution Cycle. (line 6) * Special addressing forms: Range Addresses. (line 31) * standard input: Overview. (line 18) * Standard input, processing as input: Command-Line Options. (line 183) * standard output: Overview. (line 26) * stdin: Overview. (line 18) * stdout: Overview. (line 26) * Stream editor: Introduction. (line 6) * subexpression: Back-references and Subexpressions. (line 6) * Subprocesses: The "s" Command. (line 108) * Subprocesses <1>: Extended Commands. (line 12) * Substitution of text, options: The "s" Command. (line 70) * suppressing output: Overview. (line 33) * syntax, addresses: sed script overview. (line 13) * syntax, sed commands: sed script overview. (line 13) * t, joining lines with: Branching and flow control. (line 150) * t, versus b: Branching and flow control. (line 150) * Text, appending: Other Commands. (line 45) * Text, deleting: Common Commands. (line 44) * Text, insertion: Other Commands. (line 104) * Text, printing: Common Commands. (line 52) * Text, printing after substitution: The "s" Command. (line 88) * Text, writing to a file after substitution: The "s" Command. (line 101) * Transliteration: Other Commands. (line 11) * Unbuffered I/O, choosing: Command-Line Options. (line 164) * upper-case letters: Character Classes and Bracket Expressions. (line 84) * Usage summary, printing: Command-Line Options. (line 17) * Version, printing: Command-Line Options. (line 13) * whitespace characters: Character Classes and Bracket Expressions. (line 80) * Working on separate files: Command-Line Options. (line 148) * Write first line to a file: Extended Commands. (line 80) * Write to a file: Other Commands. (line 244) * xdigit class: Character Classes and Bracket Expressions. (line 88) * Zero Address: Zero Address. (line 6) * Zero, as range start address: Range Addresses. (line 31)  File: sed.info, Node: Command and Option Index, Prev: Concept Index, Up: Top Command and Option Index ************************ This is an alphabetical list of all ‘sed’ commands and command-line options. [index] * Menu: * # (comments): Common Commands. (line 12) * --binary: Command-Line Options. (line 114) * --debug: Command-Line Options. (line 29) * --expression: Command-Line Options. (line 46) * --file: Command-Line Options. (line 51) * --follow-symlinks: Command-Line Options. (line 125) * --help: Command-Line Options. (line 17) * --in-place: Command-Line Options. (line 56) * --line-length: Command-Line Options. (line 97) * --null-data: Command-Line Options. (line 172) * --posix: Command-Line Options. (line 102) * --quiet: Command-Line Options. (line 23) * --regexp-extended: Command-Line Options. (line 135) * --sandbox: Command-Line Options. (line 157) * --separate: Command-Line Options. (line 148) * --silent: Command-Line Options. (line 23) * --unbuffered: Command-Line Options. (line 164) * --version: Command-Line Options. (line 13) * --zero-terminated: Command-Line Options. (line 172) * -b: Command-Line Options. (line 114) * -e: Command-Line Options. (line 46) * -E: Command-Line Options. (line 135) * -f: Command-Line Options. (line 51) * -i: Command-Line Options. (line 56) * -l: Command-Line Options. (line 97) * -n: Command-Line Options. (line 23) * -n, forcing from within a script: Common Commands. (line 20) * -r: Command-Line Options. (line 135) * -s: Command-Line Options. (line 148) * -u: Command-Line Options. (line 164) * -z: Command-Line Options. (line 172) * : (label) command: Programming Commands. (line 14) * = (print line number) command: Other Commands. (line 194) * {} command grouping: Common Commands. (line 91) * a (append text lines) command: Other Commands. (line 45) * alnum character class: Character Classes and Bracket Expressions. (line 44) * alpha character class: Character Classes and Bracket Expressions. (line 49) * b (branch) command: Programming Commands. (line 18) * blank character class: Character Classes and Bracket Expressions. (line 54) * c (change to text lines) command: Other Commands. (line 157) * cntrl character class: Character Classes and Bracket Expressions. (line 57) * D (delete first line) command: Other Commands. (line 255) * d (delete) command: Common Commands. (line 44) * digit character class: Character Classes and Bracket Expressions. (line 62) * e (evaluate) command: Extended Commands. (line 12) * F (File name) command: Extended Commands. (line 30) * G (appending Get) command: Other Commands. (line 288) * g (get) command: Other Commands. (line 284) * graph character class: Character Classes and Bracket Expressions. (line 65) * H (append Hold) command: Other Commands. (line 280) * h (hold) command: Other Commands. (line 276) * i (insert text lines) command: Other Commands. (line 104) * l (list unambiguously) command: Other Commands. (line 207) * lower character class: Character Classes and Bracket Expressions. (line 68) * N (append Next line) command: Other Commands. (line 261) * n (next-line) command: Common Commands. (line 61) * P (print first line) command: Other Commands. (line 273) * p (print) command: Common Commands. (line 52) * print character class: Character Classes and Bracket Expressions. (line 72) * punct character class: Character Classes and Bracket Expressions. (line 75) * q (quit) command: Common Commands. (line 28) * Q (silent Quit) command: Extended Commands. (line 36) * r (read file) command: Other Commands. (line 219) * R (read line) command: Extended Commands. (line 53) * s command, option flags: The "s" Command. (line 70) * space character class: Character Classes and Bracket Expressions. (line 80) * T (test and branch if failed) command: Extended Commands. (line 63) * t (test and branch if successful) command: Programming Commands. (line 22) * upper character class: Character Classes and Bracket Expressions. (line 84) * v (version) command: Extended Commands. (line 69) * w (write file) command: Other Commands. (line 244) * W (write first line) command: Extended Commands. (line 80) * x (eXchange) command: Other Commands. (line 292) * xdigit character class: Character Classes and Bracket Expressions. (line 88) * y (transliterate) command: Other Commands. (line 11) * z (Zap) command: Extended Commands. (line 85)  Tag Table: Node: Top738 Node: Introduction2217 Node: Invoking sed2789 Node: Overview3114 Node: Command-Line Options5561 Ref: Command-Line Options-Footnote-113530 Ref: Command-Line Options-Footnote-213758 Node: Exit status13861 Node: sed scripts14795 Node: sed script overview15394 Node: sed commands list18057 Node: The "s" Command23070 Ref: The "s" Command-Footnote-128889 Node: Common Commands28969 Node: Other Commands32106 Ref: insert command35324 Ref: Other Commands-Footnote-141629 Node: Programming Commands41709 Node: Extended Commands42649 Node: Multiple commands syntax46675 Node: sed addresses51217 Node: Addresses overview51706 Node: Numeric Addresses53705 Node: Regexp Addresses55116 Ref: Regexp Addresses-Footnote-159252 Node: Range Addresses59392 Ref: Zero Address Regex Range60294 Node: Zero Address61753 Node: sed regular expressions62318 Node: Regular Expressions Overview63172 Node: BRE vs ERE64733 Node: BRE syntax66484 Node: ERE syntax73304 Node: Character Classes and Bracket Expressions74878 Node: regexp extensions80030 Node: Back-references and Subexpressions82506 Node: Escapes84958 Ref: Escapes-Footnote-188105 Node: Locale Considerations88304 Ref: Locale Considerations-Footnote-193067 Node: advanced sed93239 Node: Execution Cycle93606 Ref: Execution Cycle-Footnote-194845 Node: Hold and Pattern Buffers95162 Node: Multiline techniques95350 Node: Branching and flow control98704 Node: Examples107029 Node: Joining lines108275 Node: Centering lines110082 Node: Increment a number111006 Ref: Increment a number-Footnote-1112495 Node: Rename files to lower case112623 Node: Print bash environment115418 Node: Reverse chars of lines116181 Ref: Reverse chars of lines-Footnote-1117224 Node: Text search across multiple lines117441 Node: Line length adjustment120786 Node: Adding a header to multiple files122533 Node: tac125986 Node: cat -n126774 Node: cat -b128616 Node: wc -c129378 Ref: wc -c-Footnote-1131316 Node: wc -w131385 Node: wc -l132875 Node: head133128 Node: tail133467 Node: uniq135196 Node: uniq -d136007 Node: uniq -u136722 Node: cat -s137435 Node: Limitations139298 Node: Other Resources140161 Node: Reporting Bugs141104 Ref: N_command_last_line142294 Ref: Reporting Bugs-Footnote-1148805 Node: GNU Free Documentation License148880 Node: Concept Index174239 Node: Command and Option Index201600  End Tag Table  Local Variables: coding: utf-8 End: