SED(1) General Commands Manual SED(1)
sed - stream editor
sed [-aEnru] [-i[extension]] command [file ...]
sed [-aEnru] [-e command] [-f command_file] [-i[extension]] [file ...]
The sed utility reads the specified files, or the standard input if no
files are specified, modifying the input as specified by a list of
commands. The input is then written to the standard output.
A single command may be specified as the first argument to sed. Multiple
commands may be specified separated by newlines or semicolons, or by
using the -e or -f options. All commands are applied to the input in the
order they are specified regardless of their origin.
The options are as follows:
-a The files listed as parameters for the w function or flag are
created (or truncated) before any processing begins, by default.
The -a option causes sed to delay opening each file until a
command containing the related w function or flag is applied to a
line of input.
-E Interpret regular expressions using POSIX extended regular
expression syntax. The default behaviour is to use POSIX basic
regular expression syntax.
Append the editing commands specified by the command argument to
the list of commands.
Append the editing commands found in the file command_file to the
list of commands. The editing commands should each be listed on
a separate line.
Edit files in place, saving backups with the specified extension.
If a zero length extension is given, no backup will be saved. It
is not recommended to give a zero length extension when in place
editing files, as it risks corruption or partial content in
situations where disk space is exhausted, etc.
-r An alias for -E, for compatibility with GNU sed.
-n By default, each line of input is echoed to the standard output
after all of the commands have been applied to it. The -n option
suppresses this behavior.
-u Force output to be line buffered, printing each line as it
becomes available. By default, output is line buffered when
standard output is a terminal and block buffered otherwise. See
setvbuf(3) for a more detailed explanation.
The form of a sed command is as follows:
Whitespace may be inserted before the first address and the function
portions of the command.
Normally, sed cyclically copies a line of input, not including its
terminating newline character, into a pattern space, (unless there is
something left after a D function), applies all of the commands with
addresses that select that pattern space, copies the pattern space to the
standard output, appending a newline, and deletes the pattern space.
Some of the functions use a hold space to save all or part of the pattern
space for subsequent retrieval.
An address is not required, but if specified must be a number (that
counts input lines cumulatively across input files), a dollar character
(`$') that addresses the last line of input, or a context address (which
consists of a regular expression preceded and followed by a delimiter).
A command line with no addresses selects every pattern space.
A command line with one address selects all of the pattern spaces that
match the address.
A command line with two addresses selects 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 that
line is selected.) Starting at the first line following the selected
range, sed starts looking again for the first address.
Editing commands can be applied to non-selected pattern spaces by use of
the exclamation character (`!') function.
SED REGULAR EXPRESSIONS
By default, sed regular expressions are basic regular expressions (BREs).
Extended regular expressions are supported using the -E and -r options.
See re_format(7) for more information on regular expressions. In
addition, sed has the following two additions to BREs:
1. In a context address, any character other than a backslash (`\') or
newline character may be used to delimit the regular expression.
The opening delimiter should be preceded by a backslash unless it is
a slash. Putting a backslash character before the delimiting
character causes the character to be treated literally. For
example, in the context address \xabc\xdefx, the RE delimiter is an
`x' and the second `x' stands for itself, so that the regular
expression is "abcxdef".
2. The escape sequence \n matches a newline character embedded in the
pattern space. You can't, however, use a literal newline character
in an address or in the substitute command.
One special feature of sed regular expressions is that they can default
to the last regular expression used. If a regular expression is empty,
i.e., just the delimiter characters are specified, the last regular
expression encountered is used instead. The last regular expression is
defined as the last regular expression used as part of an address or
substitute command, and at run-time, not compile-time. For example, the
command "/abc/s//XXX/" will substitute "XXX" for the pattern "abc".
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, as well as the w flag to the s function, take an
optional file parameter, which should be separated from the function or
flag by whitespace. Files are created (or their contents truncated)
before any input processing begins.
The b, r, s, t, w, y, and : functions all accept additional arguments.
The synopses below indicate which arguments have to be separated from the
function letters by whitespace characters.
Functions can be combined to form a function list, a list of sed
functions each followed by a newline, as follows:
The braces can be preceded and followed by whitespace. The functions can
be preceded by whitespace as well.
Functions and function lists may be preceded by an exclamation mark, in
which case they are applied only to lines that are not selected by the
Execute function-list only when the pattern space is selected.
[1 addr] a\
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.
Branch to the : function with the specified label. If the label
is not specified, branch to the end of the script.
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.
Delete the pattern space and start the next cycle.
Delete the initial segment of the pattern space through the first
newline character and start the next cycle.
Replace the contents of the pattern space with the contents of
the hold space.
Append a newline character followed by the contents of the hold
space to the pattern space.
Replace the contents of the hold space with the contents of the
Append a newline character followed by the contents of the
pattern space to the hold space.
Write text to the standard output.
(The letter ell.) Write the pattern space to the standard output
in a visually unambiguous form. This form is as follows:
vertical tab \v
Non-printable 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
newline. The end of each line is marked with a `$'.
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.
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
Write the pattern space to standard output.
Write the pattern space, up to the first newline character, to
the standard output.
Branch to the end of the script and quit without starting a new
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
condition is set.
Substitute the replacement string for the first instance of the
regular expression RE in the pattern space. Any character other
than backslash or newline can be used instead of a slash to
delimit the regular expression and the replacement. Within the
regular expression and the replacement, the regular expression
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 regular expression. 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
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
N Make the substitution only for the N'th occurrence
of the regular expression in the pattern space,
where N is a positive integer starting with 1 ...
g Make the substitution for all non-overlapping
matches of the regular expression, not just the
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.
Branch to the : function bearing the label if any substitutions
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.
Append the pattern space to the file.
Swap the contents of the pattern and hold spaces.
Replace all occurrences of characters in string1 in the pattern
space with the corresponding characters from string2. Any
character 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 any character other than a newline is that
literal character, and a backslash followed by an `n' is replaced
by a newline character.
This function does nothing; it bears a label to which the b and t
commands may branch.
Write the line number to the standard output followed by a
Empty lines are ignored.
The `#' and the remainder of the line are ignored (treated as a
comment), with the single exception that if the first two
characters in the file are `#n', the default output is
suppressed. This is the same as specifying the -n option on the
COLUMNS If set to a positive integer, output from the l function is
formatted to the given width in columns. Otherwise, sed
defaults to the terminal with, or 80 columns if the output is
not a terminal.
The sed utility exits 0 on success, and >0 if an error occurs.
The following simulates the cat(1) -s command, squeezing excess empty
lines from standard input:
$ sed -n '
# Write non-empty lines.
# Write a single empty line, then look for more empty lines.
# Get the next line, discard the held <newline> (empty line),
# and look for more empty lines.
# Write the non-empty line before going back to search
# for the first in a set of empty lines.
awk(1), ed(1), grep(1), re_format(7)
The sed utility is compliant with the IEEE Std 1003.1-2008 ("POSIX.1")
The flags [-aEiru] are extensions to that specification.
The use of newlines to separate multiple commands on the command line is
non-portable; the use of newlines to separate multiple commands within a
command file (-f command_file) is portable.
A sed command appeared in Version 7 AT&T UNIX.
The use of semicolons to separate multiple commands is not permitted for
the following commands: a, b, c, i, r, t, w, :, and #.
OpenBSD 6.2 July 19, 2017 OpenBSD 6.2
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