The
grep
utility searches any given input files,
selecting lines that match one or more patterns.
By default, a pattern matches an input line if the regular expression
(RE) in the pattern matches the input line
without its trailing newline.
An empty expression matches every line.
Each input line that matches at least one of the patterns is written
to the standard output.
grep
is used for simple patterns and
basic regular expressions
(BREs);
egrep
can handle extended regular expressions
(EREs).
See
re_format(7)
for more information on regular expressions.
fgrep
is quicker than both
grep
and
egrep,
but can only handle fixed patterns
(i.e. it does not interpret regular expressions).
Patterns may consist of one or more lines,
allowing any of the pattern lines to match a portion of the input.
zgrep,
zegrep,
and
zfgrep
act like
grep,
egrep,
and
fgrep,
respectively, but accept input files compressed with the
compress(1)
or
gzip(1)
compression utilities.
The following options are available:
-A num
Print
num
lines of trailing context after each match.
See also the
-B
and
-C
options.
-a
Treat all files as ASCII text.
Normally
grep
will simply print
“Binary file ... matches”
if files contain binary characters.
Use of this option forces
grep
to output lines matching the specified pattern.
-B num
Print
num
lines of leading context before each match.
See also the
-A
and
-C
options.
-b
The offset in bytes of a matched pattern is
displayed in front of the respective matched line.
-C
Print
num
lines of leading and trailing context surrounding each match.
The default is 2 and is equivalent to
-A2
-B2.
Note:
no whitespace may be given between the option and its argument.
-c
Only a count of selected lines is written to standard output.
-E
Interpret
pattern
as an extended regular expression
(i.e. force
grep
to behave as
egrep)).
-e pattern
Specify a pattern used during the search of the input:
an input line is selected if it matches any of the specified patterns.
This option is most useful when multiple
-e
options are used to specify multiple patterns,
or when a pattern begins with a dash
(‘-’).
-F
Interpret
pattern
as a set of fixed strings
(i.e. force
grep
to behave as
fgrep)).
-f file
Read one or more newline separated patterns from
file.
Empty pattern lines match every input line.
Newlines are not considered part of a pattern.
If
file
is empty, nothing is matched.
-G
Interpret
pattern
as a basic regular expression
(i.e. force
grep
to behave as traditional
grep)).
-H
If
-R
is specified, follow symbolic links only if they were explicitly listed
on the command line.
The default is not to follow symbolic links.
-h
Never print filename headers
(i.e. filenames)
with output lines.
-I
Ignore binary files.
-i
Perform case insensitive matching.
By default,
grep
is case sensitive.
-L
Only the names of files not containing selected lines are written to
standard output.
Pathnames are listed once per file searched.
If the standard input is searched, the string
“(standard input)”
is written.
-l
Only the names of files containing selected lines are written to
standard output.
grep
will only search a file until a match has been found,
making searches potentially less expensive.
Pathnames are listed once per file searched.
If the standard input is searched, the string
“(standard input)”
is written.
-n
Each output line is preceded by its relative line number in the file,
starting at line 1.
The line number counter is reset for each file processed.
This option is ignored if
-c,
-L,
-l,
or
-q
is
specified.
-o
Always print filename headers with output lines.
-P
If
-R
is specified, no symbolic links are followed.
This is the default.
-q
Quiet mode:
suppress normal output.
grep
will only search a file until a match has been found,
making searches potentially less expensive.
-R
Recursively search subdirectories listed.
-S
If
-R
is specified, all symbolic links are followed.
The default is not to follow symbolic links.
-s
Silent mode.
Nonexistent and unreadable files are ignored
(i.e. their error messages are suppressed).
-U
Search binary files, but do not attempt to print them.
-V
Display version information.
All other options are ignored.
-v
Selected lines are those
not
matching any of the specified patterns.
-w
The expression is searched for as a word (as if surrounded by
‘[[:<:]]’
and
‘[[:>:]]’;
see
re_format(7/)).
-x
Only input lines selected against an entire fixed string or regular
expression are considered to be matching lines.
-Z
Force
grep
to behave as
zgrep.
--binary-files
Controls searching and printing of binary files.
Options are
binary,
the default: search binary files but do not print them;
without-match:
do not search binary files;
and
text:
treat all files as text.
.Sm off
--context [= num]
.Sm on
Print
num
lines of leading and trailing context.
The default is 2.
--line-buffered
Force output to be line buffered.
By default, output is line buffered when standard output is a terminal
and block buffered otherwise.
If no file arguments are specified, the standard input is used.
RETURN VALUES
The
grep
utility exits with one of the following values:
0
One or more lines were selected.
1
No lines were selected.
\*(Gt1
An error occurred.
EXAMPLES
To find all occurrences of the word
‘patricia’
in a file:
$ grep 'patricia' myfile
To find all occurrences of the pattern
".Pp"
at the beginning of a line:
$ grep '^\e.Pp' myfile
The apostrophes ensure the entire expression is evaluated by
grep
instead of by the user's shell.
The caret
"^"
matches the null string at the beginning of a line,
and the
"\e"
escapes the
"\&.",
which would otherwise match any character.
To find all lines in a file which do not contain the words
‘foo’
or
‘bar’:
$ grep -v -e 'foo' -e 'bar' myfile
A simple example of an extended regular expression:
$ egrep '19|20|25' calendar
Peruses the file
‘calendar’
looking for either 19, 20, or 25.
The
grep
utility is compliant with the
specification.
The flags
[-AaBbCGHhILoPRSUVwZ]
are extensions to that specification, and the behaviour of the
-f
flag when used with an empty pattern file is left undefined.
All long options are provided for compatibility with
GNU versions of this utility.
Historic versions of the
grep
utility also supported the flags
[-ruy].
This implementation supports those options;
however, their use is strongly discouraged.
HISTORY
The
grep
command first appeared in
Version 6 AT&T UNIX.