Sed/Extended-Commands
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3.7 Commands Specific to GNU sed
These commands are specific to GNU sed
, so you
must use them with care and only when you are sure that
hindering portability is not evil. They allow you to check
for GNU sed
extensions or to do tasks that are required
quite often, yet are unsupported by standard sed
s.
e [command]
This command allows one to pipe input from a shell command into pattern space. Without parameters, the
e
command executes the command that is found in pattern space and replaces the pattern space with the output; a trailing newline is suppressed.If a parameter is specified, instead, the
e
command interprets it as a command and sends its output to the output stream. The command can run across multiple lines, all but the last ending with a back-slash.In both cases, the results are undefined if the command to be executed contains a NUL character.
Note that, unlike the
r
command, the output of the command will be printed immediately; ther
command instead delays the output to the end of the current cycle.F
Print out the file name of the current input file (with a trailing newline).
Q [exit-code]
This command accepts only one address.
This command is the same as
q
, but will not print the contents of pattern space. Likeq
, it provides the ability to return an exit code to the caller.This command can be useful because the only alternative ways to accomplish this apparently trivial function are to use the
-n
option (which can unnecessarily complicate your script) or resorting to the following snippet, which wastes time by reading the whole file without any visible effect::eat $d Quit silently on the last line N Read another line, silently g Overwrite pattern space each time to save memory b eat
R filename
Queue a line of
filename
to be read and inserted into the output stream at the end of the current cycle, or when the next input line is read. Note that iffilename
cannot be read, or if its end is reached, no line is appended, without any error indication.As with the
r
command, the special value/dev/stdin
is supported for the file name, which reads a line from the standard input.T label
Branch to
label
only if there have been no successfuls
ubstitutions since the last input line was read or conditional branch was taken. Thelabel
may be omitted, in which case the next cycle is started.v version
This command does nothing, but makes
sed
fail if GNUsed
extensions are not supported, simply because other versions ofsed
do not implement it. In addition, you can specify the version ofsed
that your script requires, such as4.0.5
. The default is4.0
because that is the first version that implemented this command.This command enables all GNU extensions even if
POSIXLY_CORRECT
is set in the environment.W filename
Write to the given filename the portion of the pattern space up to the first newline. Everything said under the
w
command about file handling holds here too.z
This command empties the content of pattern space. It is usually the same as ‘
s/.*//
’, but is more efficient and works in the presence of invalid multibyte sequences in the input stream. POSIX mandates that such sequences are not matched by ‘.
’, so that there is no portable way to clearsed
’s buffers in the middle of the script in most multibyte locales (including UTF-8 locales).
Next: Multiple commands syntax, Previous: Programming Commands, Up: sed scripts [Contents][Index]