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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 |
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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.1‐2017, 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.1‐2017, 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 and warning
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.1‐2017, 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.
Editing commands other than {...}, a, b, c, i, r, t, w, :, and #
can be followed by a <semicolon>, optional <blank> characters,
and another editing command. However, when an s editing command
is used with the w flag, following it with another command in
this manner produces undefined results.
A function can be preceded by a '!' character, 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 '!' character. It is unspecified whether <blank>
characters can follow the '!' character, and conforming
applications shall not follow the '!' character with <blank>
characters.
If a label argument (to a b, t, or : command) contains characters
outside of the portable filename character set, or if a label is
longer than 8 bytes, the behavior is unspecified. The
implementation shall support label arguments recognized as unique
up to at least 8 bytes; the actual length (greater than or equal
to 8) supported by the implementation is unspecified. It is
unspecified whether exceeding the maximum supported label length
causes an error or a silent truncation.
[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. The braces can
be preceded or followed by <blank> characters. The
<right-brace> shall be preceded by a <newline> or
<semicolon> (before any optional <blank> characters
preceding the <right-brace>).
Each command in the list of commands shall be
terminated by a <newline> character, or by a
<semicolon> character if permitted when the command is
used outside the braces. The editing commands can be
preceded by <blank> characters, but shall not be
followed by <blank> characters.
[1addr]a\
text Write text to standard output as described previously.
[2addr]b [label]
Branch to the : command verb bearing the label
argument. If label is not specified, branch to the end
of the script.
[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.1‐2017,
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).
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>.
The meaning of an unescaped <backslash> immediately
followed by any character other than '&', <backslash>,
a digit, <newline>, or the delimiter character used for
this command, is unspecified.
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.
When using sed to process pathnames, it is recommended that
LC_ALL, or at least LC_CTYPE and LC_COLLATE, are set to POSIX or
C in the environment, since pathnames can contain byte sequences
that do not form valid characters in some locales, in which case
the utility's behavior would be undefined. In the POSIX locale
each byte is a valid single-byte character, and therefore this
problem is avoided.
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.1‐2017 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.1‐2017 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.1‐2017 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.1‐2017, 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.1‐2017 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 referenced by a b or t command, jumps to labels that do not
exist, and label arguments that are subject to truncation.
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.1‐2017, 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 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. 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.opengroup.org/unix/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 2017 SED(1P)
Pages that refer to this page: awk(1p), csplit(1p), dd(1p), ed(1p), ex(1p), grep(1p), head(1p), od(1p), tr(1p)
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