GNU Info
(sed.info)Common Commands
Often used commands
===================
If you use SED at all, you will quite likely want to know these
commands.
`#'
[No addresses allowed.]
The `#' "command" begins a comment; the comment continues until
the next newline.
If you are concerned about portability, be aware that some
implementations of SED (which are not POSIX.2 conformant) may only
support a single one-line comment, and then only when the very
first character of the script is a `#'.
Warning: if the first two characters of the SED script are `#n',
then the `-n' (no-autoprint) option is forced. If you want to put
a comment in the first line of your script and that comment begins
with the letter `n' and you do not want this behavior, then be
sure to either use a capital `N', or place at least one space
before the `n'.
`s/REGEXP/REPLACEMENT/FLAGS'
(The `/' characters may be uniformly replaced by any other single
character within any given `s' command.)
The `/' character (or whatever other character is used in its
stead) can appear in the REGEXP or REPLACEMENT only if it is
preceded by a `\' character. Also newlines may appear in the
REGEXP using the two character sequence `\n'.
The `s' command attempts to match the pattern space against the
supplied REGEXP. If the match is successful, then that portion of
the pattern space which was matched is replaced with REPLACEMENT.
The REPLACEMENT can contain `\N' (N being a number from 1 to 9,
inclusive) references, which refer to the portion of the match
which is contained between the Nth `\(' and its matching `\)'.
Also, the REPLACEMENT can contain unescaped `&' characters which
will reference the whole matched portion of the pattern space. To
include a literal `\', `&', or newline in the final replacement,
be sure to precede the desired `\', `&', or newline in the
REPLACEMENT with a `\'.
The `s' command can be followed with zero or more of the following
FLAGS:
`g'
Apply the replacement to _all_ matches to the REGEXP, not
just the first.
`p'
If the substitution was made, then print the new pattern
space.
`NUMBER'
Only replace the NUMBERth match of the REGEXP.
`w FILE-NAME'
If the substitution was made, then write out the result to
the named file.
`I'
(This is a GNU extension.)
Match REGEXP in a case-insensitive manner.
`q'
[At most one address allowed.]
Exit SED without processing any more commands or input. Note that
the current pattern space is printed if auto-print is not disabled.
`d'
Delete the pattern space; immediately start next cycle.
`p'
Print out the pattern space (to the standard output). This
command is usually only used in conjunction with the `-n'
command-line option.
Note: some implementations of SED, such as this one, will
double-print lines when auto-print is not disabled and the `p'
command is given. Other implementations will only print the line
once. Both ways conform with the POSIX.2 standard, and so neither
way can be considered to be in error. Portable SED scripts should
thus avoid relying on either behavior; either use the `-n' option
and explicitly print what you want, or avoid use of the `p'
command (and also the `p' flag to the `s' command).
`n'
If auto-print is not disabled, print the pattern space, then,
regardless, replace the pattern space with the next line of input.
If there is no more input then SED exits without processing any
more commands.
`{ COMMANDS }'
A group of commands may be enclosed between `{' and `}' characters.
(The `}' must appear in a zero-address command context.) This is
particularly useful when you want a group of commands to be
triggered by a single address (or address-range) match.
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