man/man1/grep.1

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.Dd August 13, 2020
.Dt GREP 1
.Os
.Sh NAME
.Nm grep ,
.Nm egrep ,
.Nm fgrep
.Nd search a file for a pattern
.Sh SYNOPSIS
.Nm grep
.Op Fl E Ns | Ns Fl F
.Op Fl bchHilLnorRsqvwx
.Op Fl A Ar num
.Op Fl B Ar num
.Op Fl C Ar num Ns | Ns Fl Ns Ar num
.Op Fl -label Ns = Ns Ar name
.Oo Fl e Ar pattern_list Oc Ns ...
.Oo Fl f Ar pattern_file Oc Ns ...
.Op Ar pattern_list
.Oo Ar file Oc Ns ...
.Sh DESCRIPTION
The
.Nm
utility searches text files for a pattern and prints all lines that contain that
pattern.
If no files are specified,
.Nm
assumes standard input.
Normally, each line found is copied to standard output.
The file name is printed before each line found if there is more than one input
file.
.Pp
.Nm
handles patterns as basic regular expressions (BREs);
.Nm egrep
.Pq same as Nm Fl E
handles patterns as extended regular expressions (EREs);
.Nm fgrep
.Pq same as Nm Fl F
handles patterns as fixed strings.
.Sh OPTIONS
The following options are supported:
.Bl -tag -width Ds
.It Fl A Ar num
Prints
.Ar num
input lines of context after each matching line.
If there are multiple matching lines, their context lines are separated by a
.Ql --
delimiter line.
.It Fl b
Precedes each line by the block number on which it was found.
This can be useful in locating block numbers by context (first block is 0).
.It Fl B Ar num
Prints
.Ar num
input lines of context before each matching line.
If there are multiple matching lines, their context lines are separated by a
.Ql --
delimiter line.
.It Fl c
Prints only a count of the lines that contain the pattern.
Overrides
.Fl l
and
.Fl L .
.It Fl C Ar num Ns \&, Fl Ns Ar num
Prints
.Ar num
input lines of context before and
.Ar number
input lines of context after each matching line.
If there are multiple matching lines, their context lines are separated by a
.Ql --
delimiter line.
.It Fl e Ar pattern_list
Specifies one or more patterns to be used during the search for input.
Patterns in
.Ar pattern_list
must be separated by a NEWLINE character.
A null pattern can be specified by two adjacent newline characters in
.Ar pattern_list .
Unless the
.Fl E
or
.Fl F
option is also specified, each pattern is treated as a BRE, as described in
.Xr regex 5 .
.It Fl E
Matches using extended regular expressions.
Treats each pattern specified as an ERE, as described in
.Xr regex 5 .
If any entire ERE pattern matches an input line, the line is matched.
A null ERE matches every line.
.It Fl f Ar pattern_file
Reads one or more patterns from the file named by the path name
.Ar pattern_file .
Patterns in
.Ar pattern_file
are terminated by a NEWLINE character.
A null pattern can be specified by an empty line in
.Ar pattern_file .
Unless the
.Fl E
or
.Fl F
option is also specified, each pattern is treated as a BRE, as described in
.Xr regex 5 .
.It Fl F
Matches using fixed strings.
Treats each pattern specified as a string instead of a regular expression.
If an input line contains any of the patterns as a contiguous sequence of bytes,
the line is matched.
A null string matches every line.
.It Fl h
Prevents the name of the file containing the matching line from being prepended
to that line.
Used when searching multiple files.
.It Fl H
Precedes each line by the name of the file containing the matching line.
.It Fl i
Ignores upper/lower case distinction during comparisons.
.It Fl -label Ns = Ns Ar name
When the name of the matching file is printed
.Pq Fl H ,
instead of printing the string
.Ql (standard input)
the string
.Ar name
is printed instead.
See
.Sx Example 5 .
.It Fl l
Prints only the names of files with matching lines, separated by NEWLINE
characters.
Does not repeat the names of files when the pattern is found more than once.
If both
.Fl l
and
.Fl L
are specified, only the last specified takes effect.
Overrides
.Fl H .
.It Fl L
The opposite of the
.Fl l
flag.
Prints only the names of files without matching lines.
If both
.Fl l
and
.Fl L
are specified, only the last specified takes effect.
Overrides
.Fl H .
.It Fl n
Precedes each line by its line number in the file (first line is 1).
.It Fl o
Prints only the matching part of a line.
If a pattern appears more than once in a line, it will be matched and
printed multiple times.
.Pp
The
.Fl o
option is overridden when any of the
.Fl l ,
.Fl L ,
or
.Fl c
options are specified.
When the
.Fl o
option is specified, all context options are ignored.
The
.Fl o
and
.Fl v
options are not supported together at this time.
.It Fl q
Quiet.
Does not write anything to the standard output, regardless of matching lines.
Exits with zero status if an input line is selected.
Overrides
.Fl c ,
.Fl l ,
and
.Fl L .
.It Fl r
Read all files under each directory, recursively.
Follow symbolic links on the command line, but skip symlinks that are
encountered recursively.
If file is a device, FIFO, or socket, skip it.
.It Fl R
Read all files under each directory, recursively, following all symbolic links.
.It Fl s
Suppresses error messages about nonexistent or unreadable files.
.It Fl v
Prints all lines except those that contain the pattern.
.It Fl w
Searches for the expression as a word as if surrounded by
.Ql \e<
and
.Ql \e> .
.It Fl x
Considers only input lines that use all characters in the line to match an
entire fixed string or regular expression to be matching lines.
.El
.Sh OPERANDS
The following operands are supported:
.Bl -tag -width Ds
.It Ar file
A path name of a file to be searched for the patterns.
If no
.Ar file
operands are specified, the standard input is used.
.It Ar pattern_list
Specifies one or more patterns to be used during the search for input.
This operand is treated as if it were specified as
.Fl e Ar pattern_list .
Should not be specified if either
.Fl e
or
.Fl f
is specified.
.El
.Sh USAGE
Be careful using the characters
.Ql $ ,
.Ql * ,
.Ql \&[ ,
.Ql ^ ,
.Ql | ,
.Ql \&( ,
.Ql \&) ,
and
.Ql \e
in the
.Ar pattern_list
because they are also meaningful to the shell.
It is safest to enclose the entire
.Ar pattern_list
in single quotes:
.Li '...' .
.Pp
The
.Fl e Ar pattern
option has the same effect as the
.Ar pattern
operand, but is useful when
.Ar pattern
begins with the hyphen delimiter.
It is also useful when it is more convenient to provide multiple patterns as
separate arguments.
.Pp
Multiple
.Fl e
and
.Fl f
options are accepted and
.Nm
uses all of the patterns it is given while matching input text lines.
Notice that the order of evaluation is not specified.
If an implementation finds a null string as a pattern, it is allowed to use that
pattern first, matching every line, and effectively ignore any other patterns.
.Pp
The
.Fl q
option provides a means of easily determining whether or not a pattern (or
string) exists in a group of files.
When searching several files, it provides a performance improvement (because it
can quit as soon as it finds the first match) and requires less care by the user
in choosing the set of files to supply as arguments (because it exits zero if it
finds a match even if
.Nm
detected an access or read error on earlier file operands).
.Ss Large File Behavior
See
.Xr largefile 5
for the description of the behavior of
.Nm
when encountering files greater than or equal to 2 Gbyte (2^31 bytes).
.Sh EXIT STATUS
The following exit values are returned:
.Bl -tag -width Ds
.It Sy 0
One or more matches were found.
.It Sy 1
No matches were found.
.It Sy 2
Syntax errors or inaccessible files (even if matches were found).
.El
.Sh EXAMPLES
.Bl -tag -width Ds
.It Sy Example 1 No Finding All Uses of a Word
To find all uses of the word
.Ql Posix
(in any case) in the file
.Pa text.mm ,
and write with line numbers:
.Bd -literal
$ grep -i -n posix text.mm
.Ed
.It Sy Example 2 No Finding All Empty Lines
To find all empty lines in the standard input:
.Bd -literal
$ grep ^$
.Ed
.Pp
or
.Bd -literal
$ grep -v .
.Ed
.It Sy Example 3 No Finding Lines Containing Strings
All of the following commands print all lines containing strings
.Ql abc
or
.Ql def
or both:
.Bd -literal
$ grep 'abc
def'
$ grep -e 'abc
def'
$ grep -e 'abc' -e 'def'
$ grep -E 'abc|def'
$ grep -E -e 'abc|def'
$ grep -E -e 'abc' -e 'def'
$ grep -E 'abc
def'
$ grep -E -e 'abc
def'
$ grep -F -e 'abc' -e 'def'
$ grep -F 'abc
def'
$ grep -F -e 'abc
def'
.Ed
.It Sy Example 4 No Finding Lines with Matching Strings
Both of the following commands print all lines matching exactly
.Ql abc
or
.Ql def :
.Bd -literal
$ grep -E '^abc$
^def$'
$ grep -F -x 'abc
def'
.Ed
.It Sy Example 5 No Using Fl -label
When piping standard input into
.Nm ,
as part of a pipeline, occasionally it can be useful override the file
name
.Ql (standard input)
with something from the pipeline.
This would output each matching line instead with the name of the input
file.
.Bd -literal
$ for f in *.gz; do
> gzcat $f | grep -H --label=$f foo
> done
.Ed
.El
.Sh ENVIRONMENT VARIABLES
See
.Xr environ 5
for descriptions of the following environment variables that affect the
execution of
.Nm :
.Ev LANG , LC_ALL , LC_COLLATE , LC_CTYPE , LC_MESSAGES ,
and
.Ev NLSPATH .
.Sh CODE SET INDEPENDENCE
.Sy Enabled
.Sh INTERFACE STABILITY
.Sy Committed
.Sh SEE ALSO
.Xr sed 1 ,
.Xr sh 1 ,
.Xr attributes 5 ,
.Xr environ 5 ,
.Xr largefile 5 ,
.Xr regex 5 ,
.Xr standards 5
.Sh STANDARDS
The
.Nm
utility is compliant with the
.St -p1003.1-2008
specification with the exception of
.Fl s
option being the same as
.Fl q
in current implementation for historic reasons.
The flags
.Op Fl AbBChHrRw
are extensions to that specification.
.Sh NOTES
The results are unspecified if input files contain lines longer than
.Dv LINE_MAX
bytes or contain binary data.
.Dv LINE_MAX
is defined in
.In limits.h .
.Pp
Portable applications should use
.Nm Fl E
and
.Nm Fl F
instead of
.Nm egrep
and
.Nm fgrep ,
respectively.
.Sh HISTORY
The
.Nm grep
command first appeared in
.At v6 .
.Pp
In the past
.Pa /usr/bin/grep ,
.Pa /usr/bin/egrep ,
and
.Pa /usr/bin/fgrep
were separate implementations, and were not standard conforming, with standard
conforming ones installed as
.Pa /usr/xpg4/bin/grep ,
.Pa /usr/xpg4/bin/egrep ,
and
.Pa /usr/xpg4/bin/fgrep ,
respectively.
Now all non-conforming implementations are removed, and the ones previously
found in
.Pa /usr/xpg4/bin
are installed in
.Pa /usr/bin .