Sed Functions
In the following list of commands, the maximum number of permissible
addresses for each command is indicated by [0addr], [1addr], or [2addr],
representing zero, one, or two addresses.
The argument text consists of one or more lines. To embed a newline in
the text, precede it with a backslash. Other backslashes in text are
deleted and the following character taken literally.
The ``r'' and ``w'' functions take an optional file parameter, which
should be separated from the function letter by white space. Each file
given as an argument to sed is created (or its contents truncated) before
any input processing begins.
The ``b'', ``r'', ``s'', ``t'', ``w'', ``y'', ``!'', and ``:'' functions
all accept additional arguments. The following synopses indicate which
arguments have to be separated from the function letters by white space
characters.
Two of the functions take a function-list. This is a list of sed func-
tions separated by newlines, as follows:
{ function
function
...
function
}
The ``{'' can be preceded by white space and can be followed by white
space. The function can be preceded by white space. The terminating
``}'' must be preceded by a newline or optional white space.
[2addr] function-list
Execute function-list only when the pattern space is selected.
[1addr]a\
text Write text to standard output immediately before each attempt to
read a line of input, whether by executing the ``N'' function or
by beginning a new cycle.
[2addr]b[label]
Branch to the ``:'' function with the specified label. If the
label is not specified, branch to the end of the script.
[2addr]c\
text Delete the pattern space. With 0 or 1 address or at the end of a
2-address range, text is written to the standard output.
[2addr]d
Delete the pattern space and start the next cycle.
[2addr]D
Delete the initial segment of the pattern space through the first
newline character and start the next cycle.
[2addr]g
Replace the contents of the pattern space with the contents of
the hold space.
[2addr]G
Append a newline character followed by the contents of the hold
space to the pattern space.
[2addr]h
Replace the contents of the hold space with the contents of the
pattern space.
[2addr]H
Append a newline character followed by the contents of the pat-
tern space to the hold space.
[1addr]i\
text Write text to the standard output.
[2addr]l
(The letter ell.) Write the pattern space to the standard output
in a visually unambiguous form. This form is as follows:
backslash \\
alert \a
form-feed \f
carriage-return \r
tab \t
vertical tab \v
Nonprintable characters are written as three-digit octal numbers
(with a preceding backslash) for each byte in the character (most
significant byte first). Long lines are folded, with the point
of folding indicated by displaying a backslash followed by a new-
line. The end of each line is marked with a ``$''.
[2addr]n
Write the pattern space to the standard output if the default
output has not been suppressed, and replace the pattern space
with the next line of input.
[2addr]N
Append the next line of input to the pattern space, using an
embedded newline character to separate the appended material from
the original contents. Note that the current line number
changes.
[2addr]p
Write the pattern space to standard output.
[2addr]P
Write the pattern space, up to the first newline character to the
standard output.
[1addr]q
Branch to the end of the script and quit without starting a new
cycle.
[1addr]r file
Copy the contents of file to the standard output immediately
before the next attempt to read a line of input. If file cannot
be read for any reason, it is silently ignored and no error con-
dition is set.
[2addr]s/regular expression/replacement/flags
Substitute the replacement string for the first instance of the
regular expression in the pattern space. Any character other
than backslash or newline can be used instead of a slash to
delimit the RE and the replacement. Within the RE and the
replacement, the RE delimiter itself can be used as a literal
character if it is preceded by a backslash.
An ampersand (``&'') appearing in the replacement is replaced by
the string matching the RE. The special meaning of ``&'' in this
context can be suppressed by preceding it by a backslash. The
string ``\#'', where ``#'' is a digit, is replaced by the text
matched by the corresponding backreference expression (see
re_format(7)).
A line can be split by substituting a newline character into it.
To specify a newline character in the replacement string, precede
it with a backslash.
The value of flags in the substitute function is zero or more of
the following:
N Make the substitution only for the N'th occurrence
of the regular expression in the pattern space.
g Make the substitution for all non-overlapping
matches of the regular expression, not just the
first one.
p Write the pattern space to standard output if a
replacement was made. If the replacement string is
identical to that which it replaces, it is still
considered to have been a replacement.
w file Append the pattern space to file if a replacement
was made. If the replacement string is identical
to that which it replaces, it is still considered
to have been a replacement.
[2addr]t [label]
Branch to the ``:'' function bearing the label if any substitu-
tions have been made since the most recent reading of an input
line or execution of a ``t'' function. If no label is specified,
branch to the end of the script.
[2addr]w file
Append the pattern space to the file.
[2addr]x
Swap the contents of the pattern and hold spaces.
[2addr]y/string1/string2/
Replace all occurrences of characters in string1 in the pattern
space with the corresponding characters from string2. Any char-
acter other than a backslash or newline can be used instead of a
slash to delimit the strings. Within string1 and string2, a
backslash followed by an ``n'' is replaced by a newline charac-
ter. A pair of backslashes is replaced by a literal backslash.
Finally, a backslash followed by any other character (except a
newline) is that literal character.
[2addr]!function
[2addr]!function-list
Apply the function or function-list only to the lines that are
not selected by the address(es).
[0addr]:label
This function does nothing; it bears a label to which the ``b''
and ``t'' commands may branch.
[1addr]=
Write the line number to the standard output followed by a new-
line character.
[0addr]
Empty lines are ignored.
[0addr]#
The ``#'' and the remainder of the line are ignored (treated as a
comment), with the single exception that if the first two charac-
ters in the file are ``#n'', the default output is suppressed.
This is the same as specifying the -n option on the command line.
ENVIRONMENT
The COLUMNS, LANG, LC_ALL, LC_CTYPE and LC_COLLATE environment variables
affect the execution of sed as described in environ(7).
EXIT STATUS
The sed utility exits 0 on success, and >0 if an error occurs.
LEGACY DESCRIPTION
Warnings are not generated for unused labels. In legacy mode, they are.
In the -y function, doubled backslashes are not converted to single ones.
In legacy mode, they are.
For more information about legacy mode, see compat(5).
SEE ALSO
awk(1), ed(1), grep(1), regex(3), compat(5), re_format(7)
STANDARDS
The sed utility is expected to be a superset of the IEEE Std 1003.2
(``POSIX.2'') specification.
The -E, -a and -i options are non-standard FreeBSD extensions and may not
be available on other operating systems.
HISTORY
A sed command, written by L. E. McMahon, appeared in Version 7 AT&T UNIX.
AUTHORS
Diomidis D. Spinellis <dds@FreeBSD.org>
BUGS
Multibyte characters containing a byte with value 0x5C (ASCII `\') may be
incorrectly treated as line continuation characters in arguments to the
``a'', ``c'' and ``i'' commands. Multibyte characters cannot be used as
delimiters with the ``s'' and ``y'' commands.