BreadCrumbs: Sed Command
Sed Command
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Summary
SED(1) BSD General Commands Manual SED(1)
NAME
sed -- stream editor
SYNOPSIS
sed [-Ean] command [file ...]
sed [-Ean] [-e command] [-f command_file] [-i extension] [file ...]
DESCRIPTION
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 com-
mands. 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 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 following options are available:
-E Interpret regular expressions as extended (modern) regular
expressions rather than basic regular expressions (BRE's). The
re_format(7) manual page fully describes both formats.
-a The files listed as parameters for the ``w functions are cre-
ated (or truncated) before any processing begins, by default.
The -a option causes sed to delay opening each file until a com-
mand containing the related ``w function is applied to a line
of input.
-e command
Append the editing commands specified by the command argument to
the list of commands.
-f command_file
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.
-i extension
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 you risk corruption or partial content in situ-
ations where disk space is exhausted, etc.
-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.
The form of a sed command is as follows:
[address[,address]]function[arguments]
Whitespace may be inserted before the first address and the function por-
tions of the command.
Normally, sed cyclically copies a line of input, not including its termi-
nating newline character, into a pattern space, (unless there is some-
thing 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.
Sed Addresses
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 delim-
iter).
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 an inclusive range. This range
starts with the first pattern space that matches the first address. The
end of the range is the next following pattern space that matches the
second address. If the second address is a number less than or equal to
the line number first selected, only that line is selected. In the case
when the second address is a context address, sed does not re-match the
second address against the pattern space that matched the first address.
Starting at the first line following the selected range, sed starts look-
ing 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
The regular expressions used in sed, by default, are basic regular
expressions (BREs, see re_format(7) for more information), but extended
(modern) regular expressions can be used instead if the -E flag is given.
In addition, sed has the following two additions to regular expressions:
1. In a context address, any character other than a backslash (``\)
or newline character may be used to delimit the regular expression.
Also, 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 sub-
stitute command, and at run-time, not compile-time. For example, the
command ``/abc/s//XXX/ will substitute ``XXX for the pattern ``abc.
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 any character other than a newline is that
literal character, and a backslash followed by an ``n is
replaced by a newline 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).
DIAGNOSTICS
The sed utility exits 0 on success, and >0 if an error occurs.
SEE ALSO
awk(1), ed(1), grep(1), regex(3), 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>
BSD July 17, 2004 BSD
Examples
Remove all characters except digits. Replace all characters except digits with null.:
echo "m31uk3_1184329500.jpg" | sed 's/[^[:digit:]]//g'
Trim leading and trailing white space characters:
sed 's/^ *//;s/ *$//'