remove sections from each line of files
|
-f, --fields=LIST
select only these fields; also print any line that contains no delimiter character, unless the -s
option is specified
|
-d, --delimiter=DELIM
use DELIM instead of TAB for field delimiter
|
With no FILE, or when FILE is -, read standard input.
|
Pipelines
A pipeline is a sequence of one or more commands separated by one of the control operators | or |&. The
format for a pipeline is:
[time [-p]] [ ! ] command [ [|⎪|&] command2 ... ]
The standard output of command is connected via a pipe to the standard input of command2. This
connection is performed before any redirections specified by the command (see REDIRECTION below). If |&
is used, the standard error of command is connected to command2's standard input through the pipe; it is
shorthand for 2>&1 |. This implicit redirection of the standard error is performed after any
redirections specified by the command.
The return status of a pipeline is the exit status of the last command, unless the pipefail option is
enabled. If pipefail is enabled, the pipeline's return status is the value of the last (rightmost)
command to exit with a non-zero status, or zero if all commands exit successfully. If the reserved word
! precedes a pipeline, the exit status of that pipeline is the logical negation of the exit status as
described above. The shell waits for all commands in the pipeline to terminate before returning a value.
If the time reserved word precedes a pipeline, the elapsed as well as user and system time consumed by
its execution are reported when the pipeline terminates. The -p option changes the output format to that
specified by POSIX. When the shell is in posix mode, it does not recognize time as a reserved word if
the next token begins with a `-'. The TIMEFORMAT variable may be set to a format string that specifies
how the timing information should be displayed; see the description of TIMEFORMAT under Shell Variables
below.
When the shell is in posix mode, time may be followed by a newline. In this case, the shell displays the
total user and system time consumed by the shell and its children. The TIMEFORMAT variable may be used
to specify the format of the time information.
Each command in a pipeline is executed as a separate process (i.e., in a subshell).
|
print lines matching a pattern
|
grep searches the named input FILEs (or standard input if no files are named, or if a single hyphen-minus
(-) is given as file name) for lines containing a match to the given PATTERN. By default, grep prints
the matching lines.
|
how to execute the Perl interpreter
|
-p causes Perl to assume the following loop around your program, which makes it iterate over filename
arguments somewhat like sed:
LINE:
while (<>) {
... # your program goes here
} continue {
print or die "-p destination: $!\n";
}
If a file named by an argument cannot be opened for some reason, Perl warns you about it, and moves
on to the next file. Note that the lines are printed automatically. An error occurring during
printing is treated as fatal. To suppress printing use the -n switch. A -p overrides a -n switch.
"BEGIN" and "END" blocks may be used to capture control before or after the implicit loop, just as
in awk.
|
-e commandline
may be used to enter one line of program. If -e is given, Perl will not look for a filename in the
argument list. Multiple -e commands may be given to build up a multi-line script. Make sure to use
semicolons where you would in a normal program.
|
-P, --perl-regexp
Interpret PATTERN as a Perl regular expression (PCRE, see below). This is highly experimental and
grep -P may warn of unimplemented features.
Matching Control
-e PATTERN, --regexp=PATTERN
Use PATTERN as the pattern. This can be used to specify multiple search patterns, or to protect a
pattern beginning with a hyphen (-). (-e is specified by POSIX.)
|
-o, --only-matching
Print only the matched (non-empty) parts of a matching line, with each such part on a separate
output line.
|