grep: General Output Control
2.1.3 General Output Control
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‘-c’
‘--count’
Suppress normal output; instead print a count of matching lines for
each input file. With the ‘-v’ (‘--invert-match’) option, count
non-matching lines. (‘-c’ is specified by POSIX.)
‘--color[=WHEN]’
‘--colour[=WHEN]’
Surround the matched (non-empty) strings, matching lines, context
lines, file names, line numbers, byte offsets, and separators (for
fields and groups of context lines) with escape sequences to
display them in color on the terminal. The colors are defined by
the environment variable ‘GREP_COLORS’ and default to
‘ms=01;31:mc=01;31:sl=:cx=:fn=35:ln=32:bn=32:se=36’ for bold red
matched text, magenta file names, green line numbers, green byte
offsets, cyan separators, and default terminal colors otherwise.
The deprecated environment variable ‘GREP_COLOR’ is still
supported, but its setting does not have priority; it defaults to
‘01;31’ (bold red) which only covers the color for matched text.
WHEN is ‘never’, ‘always’, or ‘auto’.
‘-L’
‘--files-without-match’
Suppress normal output; instead print the name of each input file
from which no output would normally have been printed.
‘-l’
‘--files-with-matches’
Suppress normal output; instead print the name of each input file
from which output would normally have been printed. Scanning each
input file stops upon first match. (‘-l’ is specified by POSIX.)
‘-m NUM’
‘--max-count=NUM’
Stop after the first NUM selected lines. If the input is standard
input from a regular file, and NUM selected lines are output,
‘grep’ ensures that the standard input is positioned just after the
last selected line before exiting, regardless of the presence of
trailing context lines. This enables a calling process to resume a
search. For example, the following shell script makes use of it:
while grep -m 1 'PATTERN'
do
echo xxxx
done < FILE
But the following probably will not work because a pipe is not a
regular file:
# This probably will not work.
cat FILE |
while grep -m 1 'PATTERN'
do
echo xxxx
done
When ‘grep’ stops after NUM selected lines, it outputs any trailing
context lines. When the ‘-c’ or ‘--count’ option is also used,
‘grep’ does not output a count greater than NUM. When the ‘-v’ or
‘--invert-match’ option is also used, ‘grep’ stops after outputting
NUM non-matching lines.
‘-o’
‘--only-matching’
Print only the matched (non-empty) parts of matching lines, with
each such part on a separate output line. Output lines use the
same delimiters as input, and delimiters are null bytes if ‘-z’
(‘--null-data’) is also used (⇒Other Options).
‘-q’
‘--quiet’
‘--silent’
Quiet; do not write anything to standard output. Exit immediately
with zero status if any match is found, even if an error was
detected. Also see the ‘-s’ or ‘--no-messages’ option. (‘-q’ is
specified by POSIX.)
‘-s’
‘--no-messages’
Suppress error messages about nonexistent or unreadable files.
Portability note: unlike GNU ‘grep’, 7th Edition Unix ‘grep’ did
not conform to POSIX, because it lacked ‘-q’ and its ‘-s’ option
behaved like GNU ‘grep’’s ‘-q’ option.(1) USG-style ‘grep’ also
lacked ‘-q’ but its ‘-s’ option behaved like GNU ‘grep’’s.
Portable shell scripts should avoid both ‘-q’ and ‘-s’ and should
redirect standard and error output to ‘/dev/null’ instead. (‘-s’
is specified by POSIX.)
---------- Footnotes ----------
(1) Of course, 7th Edition Unix predated POSIX by several years!
Info Catalog
grep: Matching Control
grep: Command-line Options
grep: Output Line Prefix Control