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PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
SED(1P) POSIX Programmer's Manual SED(1P)
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
sed — stream editor
sed [−n] script [file...]
sed [−n] −e script [−e script]... [−f script_file]... [file...]
sed [−n] [−e script]... −f script_file [−f script_file]... [file...]
The sed utility is a stream editor that shall read one or more text
files, make editing changes according to a script of editing
commands, and write the results to standard output. The script shall
be obtained from either the script operand string or a combination of
the option-arguments from the −e script and −f script_file options.
The sed utility shall conform to the Base Definitions volume of
POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines, except that
the order of presentation of the −e and −f options is significant.
The following options shall be supported:
−e script Add the editing commands specified by the script option-
argument to the end of the script of editing commands.
−f script_file
Add the editing commands in the file script_file to the end
of the script of editing commands.
−n Suppress the default output (in which each line, after it
is examined for editing, is written to standard output).
Only lines explicitly selected for output are written.
If any −e or −f options are specified, the script of editing commands
shall initially be empty. The commands specified by each −e or −f
option shall be added to the script in the order specified. When each
addition is made, if the previous addition (if any) was from a −e
option, a <newline> shall be inserted before the new addition. The
resulting script shall have the same properties as the script
operand, described in the OPERANDS section.
The following operands shall be supported:
file A pathname of a file whose contents are read and edited. If
multiple file operands are specified, the named files shall
be read in the order specified and the concatenation shall
be edited. If no file operands are specified, the standard
input shall be used.
script A string to be used as the script of editing commands. The
application shall not present a script that violates the
restrictions of a text file except that the final character
need not be a <newline>.
The standard input shall be used if no file operands are specified,
and shall be used if a file operand is '−' and the implementation
treats the '−' as meaning standard input. Otherwise, the standard
input shall not be used. See the INPUT FILES section.
The input files shall be text files. The script_files named by the −f
option shall consist of editing commands.
The following environment variables shall affect the execution of
sed:
LANG Provide a default value for the internationalization
variables that are unset or null. (See the Base Definitions
volume of POSIX.1‐2008, Section 8.2, Internationalization
Variables for the precedence of internationalization
variables used to determine the values of locale
categories.)
LC_ALL If set to a non-empty string value, override the values of
all the other internationalization variables.
LC_COLLATE
Determine the locale for the behavior of ranges,
equivalence classes, and multi-character collating elements
within regular expressions.
LC_CTYPE Determine the locale for the interpretation of sequences of
bytes of text data as characters (for example, single-byte
as opposed to multi-byte characters in arguments and input
files), and the behavior of character classes within
regular expressions.
LC_MESSAGES
Determine the locale that should be used to affect the
format and contents of diagnostic messages written to
standard error.
NLSPATH Determine the location of message catalogs for the
processing of LC_MESSAGES.
Default.
The input files shall be written to standard output, with the editing
commands specified in the script applied. If the −n option is
specified, only those input lines selected by the script shall be
written to standard output.
The standard error shall be used only for diagnostic messages.
The output files shall be text files whose formats are dependent on
the editing commands given.
The script shall consist of editing commands of the following form:
[address[,address]]function
where function represents a single-character command verb from the
list in Editing Commands in sed, followed by any applicable
arguments.
The command can be preceded by <blank> characters and/or <semicolon>
characters. The function can be preceded by <blank> characters. These
optional characters shall have no effect.
In default operation, sed cyclically shall append a line of input,
less its terminating <newline> character, into the pattern space.
Reading from input shall be skipped if a <newline> was in the pattern
space prior to a D command ending the previous cycle. The sed utility
shall then apply in sequence all commands whose addresses select that
pattern space, until a command starts the next cycle or quits. If no
commands explicitly started a new cycle, then at the end of the
script the pattern space shall be copied to standard output (except
when −n is specified) and the pattern space shall be deleted.
Whenever the pattern space is written to standard output or a named
file, sed shall immediately follow it with a <newline>.
Some of the editing commands use a hold space to save all or part of
the pattern space for subsequent retrieval. The pattern and hold
spaces shall each be able to hold at least 8192 bytes.
Addresses in sed
An address is either a decimal number that counts input lines
cumulatively across files, a '$' character that addresses the last
line of input, or a context address (which consists of a BRE, as
described in Regular Expressions in sed, preceded and followed by a
delimiter, usually a <slash>).
An editing command with no addresses shall select every pattern
space.
An editing command with one address shall select each pattern space
that matches the address.
An editing command with two addresses shall select the inclusive
range from the first pattern space that matches the first address
through the next pattern space that matches the second. (If the
second address is a number less than or equal to the line number
first selected, only one line shall be selected.) Starting at the
first line following the selected range, sed shall look again for the
first address. Thereafter, the process shall be repeated. Omitting
either or both of the address components in the following form
produces undefined results:
[address[,address]]
Regular Expressions in sed
The sed utility shall support the BREs described in the Base
Definitions volume of POSIX.1‐2008, Section 9.3, Basic Regular
Expressions, with the following additions:
* In a context address, the construction "\cBREc", where c is any
character other than <backslash> or <newline>, shall be identical
to "/BRE/". If the character designated by c appears following a
<backslash>, then it shall be considered to be that literal
character, which shall not terminate the BRE. For example, in the
context address "\xabc\xdefx", the second x stands for itself, so
that the BRE is "abcxdef".
* The escape sequence '\n' shall match a <newline> embedded in the
pattern space. A literal <newline> shall not be used in the BRE
of a context address or in the substitute function.
* If an RE is empty (that is, no pattern is specified) sed shall
behave as if the last RE used in the last command applied (either
as an address or as part of a substitute command) was specified.
Editing Commands in sed
In the following list of editing commands, the maximum number of
permissible addresses for each function is indicated by [0addr],
[1addr], or [2addr], representing zero, one, or two addresses.
The argument text shall consist of one or more lines. Each embedded
<newline> in the text shall be preceded by a <backslash>. Other
<backslash> characters in text shall be removed, and the following
character shall be treated literally.
The r and w command verbs, and the w flag to the s command, take an
rfile (or wfile) parameter, separated from the command verb letter or
flag by one or more <blank> characters; implementations may allow
zero separation as an extension.
The argument rfile or the argument wfile shall terminate the editing
command. Each wfile shall be created before processing begins.
Implementations shall support at least ten wfile arguments in the
script; the actual number (greater than or equal to 10) that is
supported by the implementation is unspecified. The use of the wfile
parameter shall cause that file to be initially created, if it does
not exist, or shall replace the contents of an existing file.
The b, r, s, t, w, y, and : command verbs shall accept additional
arguments. The following synopses indicate which arguments shall be
separated from the command verbs by a single <space>.
The a and r commands schedule text for later output. The text
specified for the a command, and the contents of the file specified
for the r command, shall be written to standard output just before
the next attempt to fetch a line of input when executing the N or n
commands, or when reaching the end of the script. If written when
reaching the end of the script, and the −n option was not specified,
the text shall be written after copying the pattern space to standard
output. The contents of the file specified for the r command shall be
as of the time the output is written, not the time the r command is
applied. The text shall be output in the order in which the a and r
commands were applied to the input.
Command verbs other than {, a, b, c, i, r, t, w, :, and # can be
followed by a <semicolon>, optional <blank> characters, and another
command verb. However, when the s command verb is used with the w
flag, following it with another command in this manner produces
undefined results.
A function can be preceded by one or more '!' characters, in which
case the function shall be applied if the addresses do not select the
pattern space. Zero or more <blank> characters shall be accepted
before the first '!' character. It is unspecified whether <blank>
characters can follow a '!' character, and conforming applications
shall not follow a '!' character with <blank> characters.
[2addr] {editing command
editing command
...
} Execute a list of sed editing commands only when the
pattern space is selected. The list of sed editing commands
shall be surrounded by braces and separated by <newline>
characters, and conform to the following rules. The braces
can be preceded or followed by <blank> characters. The
editing commands can be preceded by <blank> characters, but
shall not be followed by <blank> characters. The <right-
brace> shall be preceded by a <newline> and can be preceded
or followed by <blank> characters.
[1addr]a\
text Write text to standard output as described previously.
[2addr]b [label]
Branch to the : function bearing the label. If label is
not specified, branch to the end of the script. The
implementation shall support labels recognized as unique up
to at least 8 characters; the actual length (greater than
or equal to 8) that shall be supported by the
implementation is unspecified. It is unspecified whether
exceeding a label length causes an error or a silent
truncation.
[2addr]c\
text Delete the pattern space. With a 0 or 1 address or at the
end of a 2-address range, place text on the output and
start the next cycle.
[2addr]d Delete the pattern space and start the next cycle.
[2addr]D If the pattern space contains no <newline>, delete the
pattern space and start a normal new cycle as if the d
command was issued. Otherwise, delete the initial segment
of the pattern space through the first <newline>, and start
the next cycle with the resultant pattern space and without
reading any new input.
[2addr]g Replace the contents of the pattern space by the contents
of the hold space.
[2addr]G Append to the pattern space a <newline> followed by the
contents of the hold space.
[2addr]h Replace the contents of the hold space with the contents of
the pattern space.
[2addr]H Append to the hold space a <newline> followed by the
contents of the pattern space.
[1addr]i\
text Write text to standard output.
[2addr]l (The letter ell.) Write the pattern space to standard
output in a visually unambiguous form. The characters
listed in the Base Definitions volume of POSIX.1‐2008,
Table 5-1, Escape Sequences and Associated Actions ('\\',
'\a', '\b', '\f', '\r', '\t', '\v') shall be written as the
corresponding escape sequence; the '\n' in that table is
not applicable. Non-printable characters not in that table
shall be written as one three-digit octal number (with a
preceding <backslash>) for each byte in the character (most
significant byte first).
Long lines shall be folded, with the point of folding
indicated by writing a <backslash> followed by a <newline>;
the length at which folding occurs is unspecified, but
should be appropriate for the output device. The end of
each line shall be marked with a '$'.
[2addr]n Write the pattern space to standard output if the default
output has not been suppressed, and replace the pattern
space with the next line of input, less its terminating
<newline>.
If no next line of input is available, the n command verb
shall branch to the end of the script and quit without
starting a new cycle.
[2addr]N Append the next line of input, less its terminating
<newline>, to the pattern space, using an embedded
<newline> to separate the appended material from the
original material. Note that the current line number
changes.
If no next line of input is available, the N command verb
shall branch to the end of the script and quit without
starting a new cycle or copying the pattern space to
standard output.
[2addr]p Write the pattern space to standard output.
[2addr]P Write the pattern space, up to the first <newline>, to
standard output.
[1addr]q Branch to the end of the script and quit without starting a
new cycle.
[1addr]r rfile
Copy the contents of rfile to standard output as described
previously. If rfile does not exist or cannot be read, it
shall be treated as if it were an empty file, causing no
error condition.
[2addr]s/BRE/replacement/flags
Substitute the replacement string for instances of the BRE
in the pattern space. Any character other than <backslash>
or <newline> can be used instead of a <slash> to delimit
the BRE and the replacement. Within the BRE and the
replacement, the BRE delimiter itself can be used as a
literal character if it is preceded by a <backslash>.
The replacement string shall be scanned from beginning to
end. An <ampersand> ('&') appearing in the replacement
shall be replaced by the string matching the BRE. The
special meaning of '&' in this context can be suppressed by
preceding it by a <backslash>. The characters "\n", where
n is a digit, shall be replaced by the text matched by the
corresponding back-reference expression. If the
corresponding back-reference expression does not match,
then the characters "\n" shall be replaced by the empty
string. The special meaning of "\n" where n is a digit in
this context, can be suppressed by preceding it by a
<backslash>. For each other <backslash> encountered, the
following character shall lose its special meaning (if
any). The meaning of a <backslash> immediately followed by
any character other than '&', <backslash>, a digit, or the
delimiter character used for this command, is unspecified.
A line can be split by substituting a <newline> into it.
The application shall escape the <newline> in the
replacement by preceding it by a <backslash>. A
substitution shall be considered to have been performed
even if the replacement string is identical to the string
that it replaces. Any <backslash> used to alter the default
meaning of a subsequent character shall be discarded from
the BRE or the replacement before evaluating the BRE or
using the replacement.
The value of flags shall be zero or more of:
n Substitute for the nth occurrence only of the BRE
found within the pattern space.
g Globally substitute for all non-overlapping
instances of the BRE rather than just the first
one. If both g and n are specified, the results
are unspecified.
p Write the pattern space to standard output if a
replacement was made.
w wfile Write. Append the pattern space to wfile if a
replacement was made. A conforming application
shall precede the wfile argument with one or more
<blank> characters. If the w flag is not the last
flag value given in a concatenation of multiple
flag values, the results are undefined.
[2addr]t [label]
Test. Branch to the : command verb bearing the label if any
substitutions have been made since the most recent reading
of an input line or execution of a t. If label is not
specified, branch to the end of the script.
[2addr]w wfile
Append (write) the pattern space to wfile.
[2addr]x Exchange the contents of the pattern and hold spaces.
[2addr]y/string1/string2/
Replace all occurrences of characters in string1 with the
corresponding characters in string2. If a <backslash>
followed by an 'n' appear in string1 or string2, the two
characters shall be handled as a single <newline>. If the
number of characters in string1 and string2 are not equal,
or if any of the characters in string1 appear more than
once, the results are undefined. Any character other than
<backslash> or <newline> can be used instead of <slash> to
delimit the strings. If the delimiter is not 'n', within
string1 and string2, the delimiter itself can be used as a
literal character if it is preceded by a <backslash>. If a
<backslash> character is immediately followed by a
<backslash> character in string1 or string2, the two
<backslash> characters shall be counted as a single literal
<backslash> character. The meaning of a <backslash>
followed by any character that is not 'n', a <backslash>,
or the delimiter character is undefined.
[0addr]:label
Do nothing. This command bears a label to which the b and t
commands branch.
[1addr]= Write the following to standard output:
"%d\n", <current line number>
[0addr] Ignore this empty command.
[0addr]# Ignore the '#' and the remainder of the line (treat them as
a comment), with the single exception that if the first two
characters in the script are "#n", the default output shall
be suppressed; this shall be the equivalent of specifying
−n on the command line.
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
Default.
The following sections are informative.
Regular expressions match entire strings, not just individual lines,
but a <newline> is matched by '\n' in a sed RE; a <newline> is not
allowed by the general definition of regular expression in
POSIX.1‐2008. Also note that '\n' cannot be used to match a <newline>
at the end of an arbitrary input line; <newline> characters appear in
the pattern space as a result of the N editing command.
This sed script simulates the BSD cat −s command, squeezing excess
empty lines from standard input.
sed −n '
# Write non-empty lines.
/./ {
p
d
}
# Write a single empty line, then look for more empty lines.
/^$/ p
# Get next line, discard the held <newline> (empty line),
# and look for more empty lines.
:Empty
/^$/ {
N
s/.//
b Empty
}
# Write the non-empty line before going back to search
# for the first in a set of empty lines.
p
'
The following sed command is a much simpler method of squeezing empty
lines, although it is not quite the same as cat −s since it removes
any initial empty lines:
sed −n '/./,/^$/p'
This volume of POSIX.1‐2008 requires implementations to support at
least ten distinct wfiles, matching historical practice on many
implementations. Implementations are encouraged to support more, but
conforming applications should not exceed this limit.
The exit status codes specified here are different from those in
System V. System V returns 2 for garbled sed commands, but returns
zero with its usage message or if the input file could not be opened.
The standard developers considered this to be a bug.
The manner in which the l command writes non-printable characters was
changed to avoid the historical backspace-overstrike method, and
other requirements to achieve unambiguous output were added. See the
RATIONALE for ed(1p) for details of the format chosen, which is the
same as that chosen for sed.
This volume of POSIX.1‐2008 requires implementations to provide
pattern and hold spaces of at least 8192 bytes, larger than the 4000
bytes spaces used by some historical implementations, but less than
the 20480 bytes limit used in an early proposal. Implementations are
encouraged to allocate dynamically larger pattern and hold spaces as
needed.
The requirements for acceptance of <blank> and <space> characters in
command lines has been made more explicit than in early proposals to
describe clearly the historical practice and to remove confusion
about the phrase ``protect initial blanks [sic] and tabs from the
stripping that is done on every script line'' that appears in much of
the historical documentation of the sed utility description of text.
(Not all implementations are known to have stripped <blank>
characters from text lines, although they all have allowed leading
<blank> characters preceding the address on a command line.)
The treatment of '#' comments differs from the SVID which only allows
a comment as the first line of the script, but matches BSD-derived
implementations. The comment character is treated as a command, and
it has the same properties in terms of being accepted with leading
<blank> characters; the BSD implementation has historically supported
this.
Early proposals required that a script_file have at least one non-
comment line. Some historical implementations have behaved in
unexpected ways if this were not the case. The standard developers
considered that this was incorrect behavior and that application
developers should not have to avoid this feature. A correct
implementation of this volume of POSIX.1‐2008 shall permit
script_files that consist only of comment lines.
Early proposals indicated that if −e and −f options were intermixed,
all −e options were processed before any −f options. This has been
changed to process them in the order presented because it matches
historical practice and is more intuitive.
The treatment of the p flag to the s command differs between System V
and BSD-based systems when the default output is suppressed. In the
two examples:
echo a | sed 's/a/A/p'
echo a | sed −n 's/a/A/p'
this volume of POSIX.1‐2008, BSD, System V documentation, and the
SVID indicate that the first example should write two lines with A,
whereas the second should write one. Some System V systems write the
A only once in both examples because the p flag is ignored if the −n
option is not specified.
This is a case of a diametrical difference between systems that could
not be reconciled through the compromise of declaring the behavior to
be unspecified. The SVID/BSD/System V documentation behavior was
adopted for this volume of POSIX.1‐2008 because:
* No known documentation for any historic system describes the
interaction between the p flag and the −n option.
* The selected behavior is more correct as there is no technical
justification for any interaction between the p flag and the −n
option. A relationship between −n and the p flag might imply that
they are only used together, but this ignores valid scripts that
interrupt the cyclical nature of the processing through the use
of the D, d, q, or branching commands. Such scripts rely on the p
suffix to write the pattern space because they do not make use of
the default output at the ``bottom'' of the script.
* Because the −n option makes the p flag unnecessary, any
interaction would only be useful if sed scripts were written to
run both with and without the −n option. This is believed to be
unlikely. It is even more unlikely that programmers have coded
the p flag expecting it to be unnecessary. Because the
interaction was not documented, the likelihood of a programmer
discovering the interaction and depending on it is further
decreased.
* Finally, scripts that break under the specified behavior produce
too much output instead of too little, which is easier to
diagnose and correct.
The form of the substitute command that uses the n suffix was limited
to the first 512 matches in an early proposal. This limit has been
removed because there is no reason an editor processing lines of
{LINE_MAX} length should have this restriction. The command
s/a/A/2047 should be able to substitute the 2047th occurrence of a on
a line.
The b, t, and : commands are documented to ignore leading white
space, but no mention is made of trailing white space. Historical
implementations of sed assigned different locations to the labels 'x'
and "x ". This is not useful, and leads to subtle programming
errors, but it is historical practice, and changing it could
theoretically break working scripts. Implementors are encouraged to
provide warning messages about labels that are never used or jumps to
labels that do not exist.
Historically, the sed ! and } editing commands did not permit
multiple commands on a single line using a <semicolon> as a command
delimiter. Implementations are permitted, but not required, to
support this extension.
Earlier versions of this standard allowed for implementations with
bytes other than eight bits, but this has been modified in this
version.
None.
awk(1p), ed(1p), grep(1p)
The Base Definitions volume of POSIX.1‐2008, Table 5-1, Escape
Sequences and Associated Actions, Chapter 8, Environment Variables,
Section 9.3, Basic Regular Expressions, Section 12.2, Utility Syntax
Guidelines
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) In the event of any discrepancy between this version and
the original IEEE and The Open Group Standard, the original IEEE and
The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 SED(1P)
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