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This is /home/riscos/gcc33/!gcc/docs/sed, produced by makeinfo version 4.7 from doc/sed.texi. INFO-DIR-SECTION Text creation and manipulation START-INFO-DIR-ENTRY * sed: (sed). Stream EDitor. END-INFO-DIR-ENTRY This file documents version 4.0.9 of GNU `sed', a stream editor. Copyright (C) 1998, 1999, 2001, 2002, 2003, 2004 Free Software Foundation, Inc. This document is released under the terms of the GNU Free Documentation License as published by the Free Software Foundation; either version 1.1, or (at your option) any later version. You should have received a copy of the GNU Free Documentation License along with GNU `sed'; see the file `COPYING.DOC'. If not, write to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. There are no Cover Texts and no Invariant Sections; this text, along with its equivalent in the printed manual, constitutes the Title Page. File: sed, Node: Top, Next: Introduction, Up: (dir) sed, a stream editor ******************** This file documents version 4.0.9 of GNU `sed', a stream editor. Copyright (C) 1998, 1999, 2001, 2002, 2003, 2004 Free Software Foundation, Inc. This document is released under the terms of the GNU Free Documentation License as published by the Free Software Foundation; either version 1.1, or (at your option) any later version. You should have received a copy of the GNU Free Documentation License along with GNU `sed'; see the file `COPYING.DOC'. If not, write to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. There are no Cover Texts and no Invariant Sections; this text, along with its equivalent in the printed manual, constitutes the Title Page. * Menu: * Introduction:: Introduction * Invoking sed:: Invocation * sed Programs:: `sed' programs * Examples:: Some sample scripts * Limitations:: Limitations and (non-)limitations of GNU `sed' * Other Resources:: Other resources for learning about `sed' * Reporting Bugs:: Reporting bugs * Extended regexps:: `egrep'-style regular expressions * 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. --- The detailed node listing --- sed Programs: * Addresses:: Selecting lines with `sed' * Regular Expressions:: Overview of regular expression syntax * Data Spaces:: Where `sed' buffers data * Common Commands:: Often used commands * The "s" Command:: `sed''s Swiss Army Knife * Other Commands:: Less frequently used commands * Programming Commands:: Commands for `sed' gurus * Extended Commands:: Commands specific of GNU `sed' * Escapes:: Specifying special characters Examples: * Centering lines:: * Increment a number:: * Rename files to lower case:: * Print bash environment:: * Reverse chars of lines:: * 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, 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, Node: Invoking sed, Next: sed Programs, Prev: Introduction, Up: Top 2 Invocation ************ `sed' may be invoked with the following command-line options: `-V' `--version' Print out the version of `sed' that is being run and a copyright notice, then exit. `-h' `--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. These options disable this automatic printing, and `sed' only produces output when explicitly told to via the `p' command. `-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) 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)) following this rule: 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). This option implies `-s'. `-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. `-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 less backslashes, but are a GNU extension and hence scripts that use them are not portable. *Note Extended regular expressions: Extended regexps. `-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. `-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.) `-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. 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, Node: sed Programs, Next: Examples, Prev: Invoking sed, Up: Top 3 `sed' Programs **************** 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 catenation of all of the SCRIPTs and SCRIPT-FILEs passed in. Each `sed' command consists of an optional address or address range, followed by a one-character command name and any additional command-specific code. * Menu: * Addresses:: Selecting lines with `sed' * Regular Expressions:: Overview of regular expression syntax * Data Spaces:: Where `sed' buffers data * Common Commands:: Often used commands * The "s" Command:: `sed''s Swiss Army Knife * Other Commands:: Less frequently used commands * Programming Commands:: Commands for `sed' gurus * Extended Commands:: Commands specific of GNU `sed' * Escapes:: Specifying special characters File: sed, Node: Addresses, Next: Regular Expressions, Up: sed Programs 3.1 Selecting lines with `sed' ============================== 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.) `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, to select the odd-numbered lines, one would use `1~2'; 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'. `$' 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. `/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 (`\'). Unless `POSIXLY_CORRECT' is set, 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 illegal to specify them together with the empty regular expression. If `POSIXLY_CORRECT' is set, instead, `//' is the null match: this behavior is mandated by POSIX, but it would break too many legacy `sed' scripts to blithely change GNU `sed''s default behavior. `\%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 (`\'). `/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. `/REGEXP/M' `\%REGEXP%M' The `M' modifier to regular-expression matching is a GNU `sed' extension which 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. `M' stands for `multi-line'. If no addresses are given, then all lines are matched; if one address is given, then only lines matching that address are matched. 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). 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. As a GNU extension, a line number of `0' can be used in an address specification like `0,/REGEXP/' so that REGEXP will be matched in the first input line too. 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. GNU `sed' also supports some special two-address forms: `0,ADDR2' Start out in "matched first address" state, until ADDR2 is found. This is similar to `1,ADDR2', except that if ADDR2 matches the very first line of input the 0,ADDR2 form will be at the end of its range, whereas the 1,ADDR2 form will still be at the beginning of its range. `ADDR1,+N' Matches ADDR1 and the N lines following ADDR1. `ADDR1,~N' Matches ADDR1 and the lines following ADDR1 until the next line whose input line number is a multiple of N. Appending the `!' character to the end of an address specification negates the sense of the match. That is, if the `!' character follows an address range, then only lines which do _not_ match the address range will be selected. This also works for singleton addresses, and, perhaps perversely, for the null address. File: sed, Node: Regular Expressions, Next: Data Spaces, Prev: Addresses, Up: sed Programs 3.2 Overview of Regular Expression Syntax ========================================= 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 in the subject. As a trivial example, the pattern The quick brown fox matches a portion of a subject string that is identical to itself. 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. 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 nonGNU implementations do not support this and portable scripts should instead use `\*' in these contexts. `\+' 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$*' is required by POSIX 1003.1-2001, but many non-GNU implementations do not support it and hence it is not universally portable. * Use back references (see below). `.' Matches any single character, including newline. `^' Matches the null string at beginning of line, i.e. what appears after the circumflex must appear at the beginning of line. `^#include' will match only lines where `#include' is the first thing on line--if there are spaces before, for example, the match fails. `^' acts as a special character only at the beginning of the regular expression or subexpression (that is, after `$' 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. `$' It is the same as `^', but refers to end of line. `$' also acts as a special character only at the end of the regular expression or subexpression (that is, before `$' or `\|'), and its use at the end of a subexpression is not portable. `[LIST]' `[^LIST]' Matches any single character in LIST: for example, `[aeiou]' matches all vowels. A list may include sequences like `CHAR1-CHAR2', which matches any character between (inclusive) CHAR1 and CHAR2. A leading `^' reverses the meaning of LIST, so that it matches any single character _not_ in LIST. To include `]' in the list, make it the first character (after the `^' if needed), to include `-' in the list, make it the first or last; to include `^' put it after the first character. The characters `$', `*', `.', `[', 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 `:'. Special escapes like `\n' and `\t' are recognized within LIST; this will change in a future version in `POSIXLY_CORRECT' mode. *Note Escapes::. `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 implicity numbered by counting occurrences of `\(' left-to-right. `\n' Matches the newline character. `\CHAR' Matches CHAR, where CHAR is one of `$', `*', `.', `[', `\', or `^'. Note that the only C-like backslash sequences that you can portably assume to be interpreted are `\n' and `\\'; in particular `\t' is not portable, and matches a `t' under most implementations of `sed', rather than a tab character. Note that the regular expression matcher is greedy, i.e., if two or more matches are detected, it selects the longest; if there are two or more selected with the same size, it selects the first in text. Examples: `abcdef' Matches `abcdef'. `a*b' Matches zero or more `a's followed by a single `b'. For example, `b' or `aaaaab'. `a\?b' Matches `b' or `ab'. `a\+b\+' Matches one or more `a's followed by one or more `b's: `ab' is the shortest possible match, but other examples are `aaaab' or `abbbbb' or `aaaaaabbbbbbb'. `.*' `.\+' These two both match all the characters in a string; however, the first matches every string (including the empty string), while the second matches only strings containing at least one character. `^main.*(.*)' This matches a string starting with `main', followed by an opening and closing parenthesis. The `n', `(' and `)' need not be adjacent. `^#' This matches a string beginning with `#'. `\\$' 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. `[^ tab]\+' (Here `tab' 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'. `^.\{15\}A' This matches the start of a string that contains 16 characters, the last of which is an `A'. File: sed, Node: Data Spaces, Next: Common Commands, Prev: Regular Expressions, Up: sed Programs 3.3 Where `sed' Buffers Data ============================ `sed' maintains two data buffers: the active _pattern_ space, and the auxiliary _hold_ space. In "normal" operation, `sed' reads in one line from the input stream and places it in the pattern space. This pattern space is where text manipulations occur. The hold space is initially empty, but there are commands for moving data between the pattern and hold spaces. File: sed, Node: Common Commands, Next: The "s" Command, Prev: Data Spaces, Up: sed Programs 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 conformant) 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]' This command only accepts a single address. Exit `sed' without processing any more commands or input. 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. `d' Delete the pattern space; immediately start next cycle. `p' Print out the pattern space (to the standard output). This command is usually only used in conjunction with the `-n' command-line option. Note: some implementations of `sed', such as this one, will double-print lines when auto-print is not disabled and the `p' command is given. Other implementations will only print the line once. Both ways conform with the POSIX standard, and so neither way can be considered to be in error. Portable `sed' scripts should thus avoid relying on either behavior; either use the `-n' option and explicitly print what you want, or avoid use of the `p' command (and also the `p' flag to the `s' command). `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. `{ 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. File: sed, Node: The "s" Command, Next: Other Commands, Prev: Common Commands, Up: sed Programs 3.5 The `s' Command =================== The syntax of the `s' (as in substitute) command is `s/REGEXP/REPLACEMENT/FLAGS'. 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. The `s' command is probably the most important in `sed' and has a lot of different options. Its basic concept is simple: the `s' command attempts to match the pattern space against the supplied REGEXP; if the match is successful, then that portion of the pattern space which was matched is replaced with REPLACEMENT. 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. Finally (this is 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'. 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. 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 FILE-NAME' If the substitution was made, then write out the result to the named file. As a GNU `sed' extension, two special values of FILE-NAME 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 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. `M' stands for `multi-line'. ---------- Footnotes ---------- (1) This is equivalent to `p' unless the `-i' option is being used. File: sed, Node: Other Commands, Next: Programming Commands, Prev: The "s" Command, Up: sed Programs 3.6 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/' (The `/' characters may be uniformly replaced by any other single character within any given `y' command.) Transliterate any characters in the pattern space which match any of the SOURCE-CHARS with the corresponding character in DEST-CHARS. 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). `a\' `TEXT' In `POSIXLY_CORRECT' mode, this command only accepts a single address. Queue 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, if between the `a' and the newline there is other than a whitespace-`\' sequence, then the text of this line, starting at the first non-whitespace character after the `a', is taken as the first line of the TEXT block. (This enables a simplification in scripting a one-line add.) This extension also works with the `i' and `c' commands. `i\' `TEXT' In `POSIXLY_CORRECT' mode, this command only accepts a single address. Immediately output the lines of text which follow this command (each but the last ending with a `\', which are removed from the output). `c\' `TEXT' Delete the lines matching the address or address-range, and output the lines of text which follow this command (each but the last ending with a `\', which are removed from the output) in place of the last line (or in place of each line, if no addresses were specified). A new cycle is started after this command is done, since the pattern space will have been deleted. `=' In `POSIXLY_CORRECT' mode, this command only accepts a single address. Print out the current input line number (with a trailing newline). `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' In `POSIXLY_CORRECT' mode, this command only accepts a single address. 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. `w FILENAME' Write the pattern space to FILENAME. As a GNU `sed' extension, two special values of FILE-NAME 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 `w' flag on successful `s' commands) which refer to the same FILENAME are output without closing and reopening the file. `D' Delete text in the pattern space up to the first newline. If any text is left, restart cycle with the resultant pattern space (without reading a new line of input), otherwise start a normal new cycle. `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 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, Node: Programming Commands, Next: Extended Commands, Prev: Other Commands, Up: sed Programs 3.7 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, Node: Extended Commands, Next: Escapes, Prev: Programming Commands, Up: sed Programs 3.8 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 (like `r' does). 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. `L N' In `POSIXLY_CORRECT' mode, this command only accepts a single address. This GNU `sed' extension fills and joins lines in pattern space to produce output lines of (at most) N characters, like `fmt' does; if N is omitted, the default as specified on the command line is used. Blank lines, spaces between words, and indentation are preserved in the output; successive input lines with different indentation are not joined; tabs are expanded to 8 columns. If the pattern space contains multiple lines, they are joined, but since the pattern space usually contains a single line, the behavior of a simple `L;d' script is the same as `fmt -s' (i.e., it does not join short lines to form longer ones). N specifies the desired line-wrap length; if omitted, the default as specified on the command line is used. `Q [EXIT-CODE]' This command only accepts a single 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 commands also enables GNU extensions unconditionally, 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. File: sed, Node: Escapes, Prev: Extended Commands, Up: sed Programs 3.9 GNU Extensions for Escapes in Regular Expressions ===================================================== 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. Other escapes match a particular character class and are valid only in regular expressions: `\w' Matches any "word" character. A "word" character is any letter or digit or the underscore character. `\W' Matches any "non-word" character. `\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. `\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. `\`' Matches only at the start of pattern space. This is different from `^' in multi-line mode. `\'' Matches only at the end of pattern space. This is different from `$' in multi-line mode. ---------- Footnotes ---------- (1) All the escapes introduced here are GNU extensions, with the exception of `\n'. File: sed, Node: Examples, Next: Limitations, Prev: sed Programs, Up: Top 4 Some Sample Scripts ********************* Here are some `sed' scripts to guide you in the art of mastering `sed'. * Menu: Some exotic examples: * Centering lines:: * Increment a number:: * Rename files to lower case:: * Print bash environment:: * Reverse chars of lines:: 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, Node: Centering lines, Next: Increment a number, Up: Examples 4.1 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 } # del leading and trailing spaces y/tab/ / 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, Node: Increment a number, Next: Rename files to lower case, Prev: Centering lines, Up: Examples 4.2 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 leading 9s by _ (any other character except digits, could # be used) :d s/9$_*$$/_\1/ td # incr last digit only. The first line adds a most-significant # digit of 1 if we have to add a digit. # # The `tn' commands are not necessary, but make the thing # faster s/^$_*$$/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, Node: Rename files to lower case, Next: Print bash environment, Prev: Increment a number, Up: Examples 4.3 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 nothing /^.*\/$.*$\n\1/b # now, transform path/fromfile\n, into # mv path/fromfile path/tofile and print it s/^$.*\/$$.*$\n$.*$$/mv \1\2 \1\3/p ' | $apply_cmd File: sed, Node: Print bash environment, Next: Reverse chars of lines, Prev: Rename files to lower case, Up: Examples 4.4 Print `bash' Environment ============================ This script strips the definition of the shell functions from the output of the `set' Bourne-shell command. #!/bin/sh set | sed -n ' :x # if no occurrence of "=()" print and load next line /=()/! { p; b; } / () $/! { p; b; } # possible start of functions section # save the line in case this is a var like FOO="() " h # if the next line has a brace, we quit because # nothing comes after functions n /^{/ q # print the old line x; p # work on the new line now x; bx ' File: sed, Node: Reverse chars of lines, Next: tac, Prev: Print bash environment, Up: Examples 4.5 Reverse Characters of Lines =============================== This script can be used to reverse the position of characters in lines. The technique moves two characters at a time, hence it is faster than more intuitive implementations. Note the `tx' command before the definition of the label. This is often needed to reset the flag that is tested by the `t' command. Imaginative readers will find uses for this script. An example is reversing the output of `banner'.(1) #!/usr/bin/sed -f /../! b # Reverse a line. Begin embedding the line between two newlines s/^.*$/\ &\ / # Move first character at the end. The regexp matches until # there are zero or one characters between the markers tx :x s/$\n.$$.*$$.\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, Node: tac, Next: cat -n, Prev: Reverse chars of lines, Up: Examples 4.6 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, Node: cat -n, Next: cat -b, Prev: tac, Up: Examples 4.7 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.*$// # compose the new number, remove the newline implicitly added by G G s/\n// h File: sed, Node: cat -b, Next: wc -c, Prev: cat -n, Up: Examples 4.8 Numbering Non-blank Lines ============================= Emulating `cat -b' is almost the same as `cat -n'--we only have to select which lines are to be numbered and which are not. The part that is common to this script and the previous one is not commented to show how important it is to comment `sed' scripts properly... #!/usr/bin/sed -nf /^$/ { 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, Node: wc -c, Next: wc -w, Prev: cat -b, Up: Examples 4.9 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 tenths and so on: we simply add the number of characters on the current line as units, and then propagate the carry to tenths, hundredths, 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 tenths 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, Node: wc -w, Next: wc -l, Prev: wc -c, Up: Examples 4.10 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/[ tab][ tab]*/ /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, Node: wc -l, Next: head, Prev: wc -w, Up: Examples 4.11 Counting Lines =================== No strange things are done now, because `sed' gives us `wc -l' functionality for free!!! Look: #!/usr/bin/sed -nf $= File: sed, Node: head, Next: tail, Prev: wc -l, Up: Examples 4.12 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, Node: tail, Next: uniq, Prev: head, Up: Examples 4.13 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 File: sed, Node: uniq, Next: uniq -d, Prev: tail, Up: Examples 4.14 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 mantain a 2-line window using `P' and `D'. This technique is often used in advanced `sed' scripts. File: sed, Node: uniq -d, Next: uniq -u, Prev: uniq, Up: Examples 4.15 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, Node: uniq -u, Next: cat -s, Prev: uniq -d, Up: Examples 4.16 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, Node: cat -s, Prev: uniq -u, Up: Examples 4.17 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 exploting the fact that `sed' cycles back to the top of 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, Node: Limitations, Next: Other Resources, Prev: Examples, Up: Top 5 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, Node: Other Resources, Next: Reporting Bugs, Prev: Limitations, Up: Top 6 Other Resources for Learning About `sed' ****************************************** In addition to several books that have been written about `sed' (either specifically or as chapters in books which discuss shell programming), one can find out more about `sed' (including suggestions of a few books) from the FAQ for the `sed-users' mailing list, available from any of: `http://www.student.northpark.edu/pemente/sed/sedfaq.html' `http://sed.sf.net/grabbag/tutorials/sedfaq.html' Also of interest are `http://www.student.northpark.edu/pemente/sed/index.htm' and `http://sed.sf.net/grabbag', which include `sed' tutorials and other `sed'-related goodies. The `sed-users' mailing list itself maintained by Sven Guckes. To subscribe, visit `http://groups.yahoo.com' and search for the `sed-users' mailing list. File: sed, Node: Reporting Bugs, Next: Extended regexps, Prev: Other Resources, Up: Top 7 Reporting Bugs **************** Email bug reports to <bonzini@gnu.org>. Be sure to include the word "sed" somewhere in the `Subject:' field. 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. `sed -n' and `s/REGEX/`replace'/p' Some versions of `sed' ignore the `p' (print) option of an `s' command unless the `-n' command-line option has been specified. Other versions always honor the `p' option. Both approaches are allowed by POSIX and GNU `sed' is the better when you write complex scripts and also more intuitive, but portable scripts should be written to work correctly with either behavior. `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. 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 `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'. 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 filesystem 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 writeable file in a read-only directory (but unbelievably nobody reports that as a bug...). ---------- Footnotes ---------- (1) which is the actual "bug" that prompted the change in behavior File: sed, Node: Extended regexps, Next: Concept Index, Prev: Reporting Bugs, Up: Top Appendix A Extended regular expressions *************************************** The only difference between basic and extended regular expressions is in the behavior of a few characters: `?', `+', parentheses, and braces (`{}'). 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_. 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. File: sed, Node: Concept Index, Next: Command and Option Index, Prev: Extended regexps, 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: * Additional reading about sed: Other Resources. (line 6) * ADDR1,+N: Addresses. (line 80) * ADDR1,~N: Addresses. (line 80) * Address, as a regular expression: Addresses. (line 27) * Address, last line: Addresses. (line 22) * Address, numeric: Addresses. (line 8) * Addresses, in sed scripts: Addresses. (line 6) * Append hold space to pattern space: Other Commands. (line 126) * Append next input line to pattern space: Other Commands. (line 106) * Append pattern space to hold space: Other Commands. (line 118) * Appending text after a line: Other Commands. (line 28) * Backreferences, in regular expressions: The "s" Command. (line 19) * Branch to a label, if s/// failed: Extended Commands. (line 76) * Branch to a label, if s/// succeeded: Programming Commands. (line 22) * Branch to a label, unconditionally: Programming Commands. (line 18) * Buffer spaces, pattern and hold: Data Spaces. (line 6) * Bugs, reporting: Reporting Bugs. (line 6) * Case-insensitive matching: The "s" Command. (line 94) * Caveat -- #n on first line: Common Commands. (line 20) * Command groups: Common Commands. (line 61) * Comments, in scripts: Common Commands. (line 12) * Conditional branch <1>: Extended Commands. (line 76) * Conditional branch: Programming Commands. (line 22) * Copy hold space into pattern space: Other Commands. (line 122) * Copy pattern space into hold space: Other Commands. (line 114) * Delete first line from pattern space: Other Commands. (line 100) * Disabling autoprint, from command line: Invoking sed. (line 21) * empty regular expression: Addresses. (line 31) * Evaluate Bourne-shell commands: Extended Commands. (line 12) * Evaluate Bourne-shell commands, after substitution: The "s" Command. (line 85) * Exchange hold space with pattern space: Other Commands. (line 130) * Excluding lines: Addresses. (line 95) * Extended regular expressions, choosing: Invoking sed. (line 56) * Extended regular expressions, syntax: Extended regexps. (line 6) * Files to be processed as input: Invoking sed. (line 94) * Flow of control in scripts: Programming Commands. (line 11) * Global substitution: The "s" Command. (line 51) * GNU extensions, /dev/stderr file <1>: Other Commands. (line 89) * GNU extensions, /dev/stderr file: The "s" Command. (line 78) * GNU extensions, /dev/stdin file <1>: Extended Commands. (line 66) * GNU extensions, /dev/stdin file: Other Commands. (line 79) * GNU extensions, /dev/stdout file <1>: Other Commands. (line 89) * GNU extensions, /dev/stdout file <2>: The "s" Command. (line 78) * GNU extensions, /dev/stdout file: Invoking sed. (line 102) * GNU extensions, 0 address: Addresses. (line 68) * GNU extensions, 0,ADDR2 addressing: Addresses. (line 80) * GNU extensions, ADDR1,+N addressing: Addresses. (line 80) * GNU extensions, ADDR1,~N addressing: Addresses. (line 80) * GNU extensions, branch if s/// failed: Extended Commands. (line 76) * GNU extensions, case modifiers in s commands: The "s" Command. (line 23) * GNU extensions, checking for their presence: Extended Commands. (line 82) * GNU extensions, evaluating Bourne-shell commands <1>: Extended Commands. (line 12) * GNU extensions, evaluating Bourne-shell commands: The "s" Command. (line 85) * GNU extensions, extended regular expressions: Invoking sed. (line 56) * GNU extensions, g and NUMBER modifier interaction in s command: The "s" Command. (line 57) * GNU extensions, I modifier <1>: The "s" Command. (line 94) * GNU extensions, I modifier: Addresses. (line 52) * GNU extensions, in-place editing <1>: Reporting Bugs. (line 83) * GNU extensions, in-place editing: Invoking sed. (line 28) * GNU extensions, L command: Extended Commands. (line 29) * GNU extensions, M modifier: The "s" Command. (line 99) * GNU extensions, modifiers and the empty regular expression: Addresses. (line 31) * GNU extensions, N~M addresses: Addresses. (line 13) * GNU extensions, quitting silently: Extended Commands. (line 49) * GNU extensions, R command: Extended Commands. (line 66) * GNU extensions, reading a file a line at a time: Extended Commands. (line 66) * GNU extensions, reformatting paragraphs: Extended Commands. (line 29) * GNU extensions, returning an exit code <1>: Extended Commands. (line 49) * GNU extensions, returning an exit code: Common Commands. (line 30) * GNU extensions, setting line length: Other Commands. (line 65) * GNU extensions, special escapes <1>: Reporting Bugs. (line 76) * GNU extensions, special escapes: Escapes. (line 6) * GNU extensions, special two-address forms: Addresses. (line 80) * GNU extensions, subprocesses <1>: Extended Commands. (line 12) * GNU extensions, subprocesses: The "s" Command. (line 85) * GNU extensions, to basic regular expressions <1>: Reporting Bugs. (line 59) * GNU extensions, to basic regular expressions: Regular Expressions. (line 26) * GNU extensions, unlimited line length: Limitations. (line 6) * GNU extensions, writing first line to a file: Extended Commands. (line 93) * Goto, in scripts: Programming Commands. (line 18) * Greedy regular expression matching: Regular Expressions. (line 135) * Grouping commands: Common Commands. (line 61) * Hold space, appending from pattern space: Other Commands. (line 118) * Hold space, appending to pattern space: Other Commands. (line 126) * Hold space, copy into pattern space: Other Commands. (line 122) * Hold space, copying pattern space into: Other Commands. (line 114) * Hold space, definition: Data Spaces. (line 6) * Hold space, exchange with pattern space: Other Commands. (line 130) * In-place editing <1>: Reporting Bugs. (line 83) * In-place editing: Invoking sed. (line 28) * Inserting text before a line: Other Commands. (line 45) * Labels, in scripts: Programming Commands. (line 14) * Last line, selecting: Addresses. (line 22) * Line length, setting <1>: Other Commands. (line 65) * Line length, setting: Invoking sed. (line 50) * Line number, printing: Other Commands. (line 62) * Line selection: Addresses. (line 6) * Line, selecting by number: Addresses. (line 8) * Line, selecting by regular expression match: Addresses. (line 27) * Line, selecting last: Addresses. (line 22) * List pattern space: Other Commands. (line 65) * Mixing g and NUMBER modifiers in the s command: The "s" Command. (line 57) * Next input line, append to pattern space: Other Commands. (line 106) * Next input line, replace pattern space with: Common Commands. (line 55) * Non-bugs, in-place editing: Reporting Bugs. (line 83) * Non-bugs, N command on the last line: Reporting Bugs. (line 39) * Non-bugs, p command and -n flag <1>: Reporting Bugs. (line 31) * Non-bugs, p command and -n flag: Common Commands. (line 49) * Non-bugs, regex syntax clashes: Reporting Bugs. (line 59) * Parenthesized substrings: The "s" Command. (line 19) * Pattern space, definition: Data Spaces. (line 6) * Perl-style regular expressions, multiline: Addresses. (line 57) * Portability, comments: Common Commands. (line 15) * Portability, line length limitations: Limitations. (line 6) * Portability, N command on the last line: Reporting Bugs. (line 39) * Portability, p command and -n flag <1>: Reporting Bugs. (line 31) * Portability, p command and -n flag: Common Commands. (line 49) * POSIXLY_CORRECT behavior, bracket expressions: Regular Expressions. (line 97) * POSIXLY_CORRECT behavior, empty regular expression: Addresses. (line 31) * POSIXLY_CORRECT behavior, escapes: Escapes. (line 11) * POSIXLY_CORRECT behavior, N command: Reporting Bugs. (line 54) * POSIXLY_CORRECT behavior, two addresses <1>: Extended Commands. (line 26) * POSIXLY_CORRECT behavior, two addresses: Other Commands. (line 25) * Print first line from pattern space: Other Commands. (line 111) * Printing line number: Other Commands. (line 62) * Printing text unambiguously: Other Commands. (line 65) * Quitting <1>: Extended Commands. (line 49) * Quitting: Common Commands. (line 30) * Range of lines: Addresses. (line 68) * Range with start address of zero: Addresses. (line 80) * Read next input line: Common Commands. (line 55) * Read text from a file <1>: Extended Commands. (line 66) * Read text from a file: Other Commands. (line 79) * Reformat pattern space: Extended Commands. (line 29) * Reformatting paragraphs: Extended Commands. (line 29) * Replace hold space with copy of pattern space: Other Commands. (line 114) * Replace pattern space with copy of hold space: Other Commands. (line 122) * Replacing all text matching regexp in a line: The "s" Command. (line 51) * Replacing only Nth match of regexp in a line: The "s" Command. (line 55) * Replacing selected lines with other text: Other Commands. (line 51) * Requiring GNU sed: Extended Commands. (line 82) * Script structure: sed Programs. (line 6) * Script, from a file: Invoking sed. (line 86) * Script, from command line: Invoking sed. (line 81) * sed program structure: sed Programs. (line 6) * Selecting lines to process: Addresses. (line 6) * Selecting non-matching lines: Addresses. (line 95) * Several lines, selecting: Addresses. (line 68) * Slash character, in regular expressions: Addresses. (line 44) * Spaces, pattern and hold: Data Spaces. (line 6) * Special addressing forms: Addresses. (line 80) * Standard input, processing as input: Invoking sed. (line 96) * Stream editor: Introduction. (line 6) * Subprocesses <1>: Extended Commands. (line 12) * Subprocesses: The "s" Command. (line 85) * Substitution of text, options: The "s" Command. (line 47) * Text, appending: Other Commands. (line 28) * Text, deleting: Common Commands. (line 36) * Text, insertion: Other Commands. (line 45) * Text, printing: Common Commands. (line 39) * Text, printing after substitution: The "s" Command. (line 65) * Text, writing to a file after substitution: The "s" Command. (line 78) * Transliteration: Other Commands. (line 14) * Unbuffered I/O, choosing: Invoking sed. (line 74) * Usage summary, printing: Invoking sed. (line 15) * Version, printing: Invoking sed. (line 10) * Working on separate files: Invoking sed. (line 64) * Write first line to a file: Extended Commands. (line 93) * Write to a file: Other Commands. (line 89) * Zero, as range start address: Addresses. (line 80) File: sed, 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) * --expression: Invoking sed. (line 81) * --file: Invoking sed. (line 86) * --help: Invoking sed. (line 15) * --in-place: Invoking sed. (line 28) * --line-length: Invoking sed. (line 50) * --quiet: Invoking sed. (line 21) * --regexp-extended: Invoking sed. (line 56) * --silent: Invoking sed. (line 21) * --unbuffered: Invoking sed. (line 74) * --version: Invoking sed. (line 10) * -e: Invoking sed. (line 81) * -f: Invoking sed. (line 86) * -h: Invoking sed. (line 15) * -i: Invoking sed. (line 28) * -l: Invoking sed. (line 50) * -n: Invoking sed. (line 21) * -n, forcing from within a script: Common Commands. (line 20) * -r: Invoking sed. (line 56) * -u: Invoking sed. (line 74) * -V: Invoking sed. (line 10) * : (label) command: Programming Commands. (line 14) * = (print line number) command: Other Commands. (line 62) * a (append text lines) command: Other Commands. (line 28) * b (branch) command: Programming Commands. (line 18) * c (change to text lines) command: Other Commands. (line 51) * D (delete first line) command: Other Commands. (line 100) * d (delete) command: Common Commands. (line 36) * e (evaluate) command: Extended Commands. (line 12) * G (appending Get) command: Other Commands. (line 126) * g (get) command: Other Commands. (line 122) * H (append Hold) command: Other Commands. (line 118) * h (hold) command: Other Commands. (line 114) * i (insert text lines) command: Other Commands. (line 45) * L (fLow paragraphs) command: Extended Commands. (line 29) * l (list unambiguously) command: Other Commands. (line 65) * N (append Next line) command: Other Commands. (line 106) * n (next-line) command: Common Commands. (line 55) * P (print first line) command: Other Commands. (line 111) * p (print) command: Common Commands. (line 39) * q (quit) command: Common Commands. (line 30) * Q (silent Quit) command: Extended Commands. (line 49) * r (read file) command: Other Commands. (line 79) * R (read line) command: Extended Commands. (line 66) * s command, option flags: The "s" Command. (line 47) * T (test and branch if failed) command: Extended Commands. (line 76) * t (test and branch if successful) command: Programming Commands. (line 22) * v (version) command: Extended Commands. (line 82) * w (write file) command: Other Commands. (line 89) * W (write first line) command: Extended Commands. (line 93) * x (eXchange) command: Other Commands. (line 130) * y (transliterate) command: Other Commands. (line 14) * {} command grouping: Common Commands. (line 61) Tag Table: Node: Top947 Node: Introduction3874 Node: Invoking sed4423 Ref: Invoking sed-Footnote-18225 Ref: Invoking sed-Footnote-28417 Node: sed Programs8524 Node: Addresses9676 Node: Regular Expressions14267 Node: Data Spaces21849 Node: Common Commands22380 Node: The "s" Command24917 Ref: The "s" Command-Footnote-129254 Node: Other Commands29326 Ref: Other Commands-Footnote-134432 Node: Programming Commands34504 Node: Extended Commands35413 Node: Escapes39514 Ref: Escapes-Footnote-142519 Node: Examples42607 Node: Centering lines43698 Node: Increment a number44585 Ref: Increment a number-Footnote-146140 Node: Rename files to lower case46260 Node: Print bash environment48943 Node: Reverse chars of lines49693 Ref: Reverse chars of lines-Footnote-150689 Node: tac50906 Node: cat -n51668 Node: cat -b53485 Node: wc -c54227 Ref: wc -c-Footnote-156138 Node: wc -w56207 Node: wc -l57666 Node: head57905 Node: tail58231 Node: uniq59662 Node: uniq -d60445 Node: uniq -u61151 Node: cat -s61857 Node: Limitations63727 Node: Other Resources64563 Node: Reporting Bugs65485 Ref: Reporting Bugs-Footnote-170301 Node: Extended regexps70372 Node: Concept Index71553 Node: Command and Option Index86123 End Tag Table