GREP(1) User Commands GREP(1)

grep, egrep, fgrep — search a file for a pattern

grep [-E|-F] [-bchHilLnorRsqvwx] [-A num] [-B num] [-C num|-num] [--label=name] [-e pattern_list]... [-f pattern_file]... [pattern_list] [file]...

The grep utility searches text files for a pattern and prints all lines that contain that pattern. If no files are specified, grep 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.

grep handles patterns as basic regular expressions (BREs); egrep (same as grep -E) handles patterns as extended regular expressions (EREs); fgrep (same as grep -F) handles patterns as fixed strings.

The following options are supported:

num
Prints num input lines of context after each matching line. If there are multiple matching lines, their context lines are separated by a ‘--’ delimiter line.
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).
num
Prints num input lines of context before each matching line. If there are multiple matching lines, their context lines are separated by a ‘--’ delimiter line.
Prints only a count of the lines that contain the pattern. Overrides -l and -L.
num, -num
Prints num input lines of context before and number input lines of context after each matching line. If there are multiple matching lines, their context lines are separated by a ‘--’ delimiter line.
pattern_list
Specifies one or more patterns to be used during the search for input. Patterns in pattern_list must be separated by a NEWLINE character. A null pattern can be specified by two adjacent newline characters in pattern_list. Unless the -E or -F option is also specified, each pattern is treated as a BRE, as described in regex(7).
Matches using extended regular expressions. Treats each pattern specified as an ERE, as described in regex(7). If any entire ERE pattern matches an input line, the line is matched. A null ERE matches every line.
pattern_file
Reads one or more patterns from the file named by the path name pattern_file. Patterns in pattern_file are terminated by a NEWLINE character. A null pattern can be specified by an empty line in pattern_file. Unless the -E or -F option is also specified, each pattern is treated as a BRE, as described in regex(7).
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.
Prevents the name of the file containing the matching line from being prepended to that line. Used when searching multiple files.
Precedes each line by the name of the file containing the matching line.
Ignores upper/lower case distinction during comparisons.
=name
When the name of the matching file is printed (-H), instead of printing the string ‘(standard input)’ the string name is printed instead. See Example 5.
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 -l and -L are specified, only the last specified takes effect. Overrides -H.
The opposite of the -l flag. Prints only the names of files without matching lines. If both -l and -L are specified, only the last specified takes effect. Overrides -H.
Precedes each line by its line number in the file (first line is 1).
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.

The -o option is overridden when any of the -l, -L, or -c options are specified. When the -o option is specified, all context options are ignored. The -o and -v options are not supported together at this time.

Quiet. Does not write anything to the standard output, regardless of matching lines. Exits with zero status if an input line is selected. Overrides -c, -l, and -L.
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.
Read all files under each directory, recursively, following all symbolic links.
Suppresses error messages about nonexistent or unreadable files.
Prints all lines except those that contain the pattern.
Searches for the expression as a word as if surrounded by ‘\<’ and ‘\>’.
Considers only input lines that use all characters in the line to match an entire fixed string or regular expression to be matching lines.

The following operands are supported:

file
A path name of a file to be searched for the patterns. If no file operands are specified, the standard input is used.
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 -e pattern_list. Should not be specified if either -e or -f is specified.

Be careful using the characters ‘$’, ‘*’, ‘[’, ‘^’, ‘|’, ‘(’, ‘)’, and ‘\’ in the pattern_list because they are also meaningful to the shell. It is safest to enclose the entire pattern_list in single quotes: '...'.

The -e pattern option has the same effect as the pattern operand, but is useful when pattern begins with the hyphen delimiter. It is also useful when it is more convenient to provide multiple patterns as separate arguments.

Multiple -e and -f options are accepted and grep 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.

The -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 grep detected an access or read error on earlier file operands).

See largefile(7) for the description of the behavior of grep when encountering files greater than or equal to 2 Gbyte (2^31 bytes).

The following exit values are returned:

One or more matches were found.
No matches were found.
Syntax errors or inaccessible files (even if matches were found).

Finding All Uses of a Word
To find all uses of the word ‘Posix’ (in any case) in the file text.mm, and write with line numbers: 
$ grep -i -n posix text.mm
Finding All Empty Lines
To find all empty lines in the standard input: 
$ grep ^$

or

$ grep -v .
Finding Lines Containing Strings
All of the following commands print all lines containing strings ‘abc’ or ‘def’ or both: 
$ 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'
Finding Lines with Matching Strings
Both of the following commands print all lines matching exactly ‘abc’ or ‘def’: 
$ grep -E '^abc$
^def$'
$ grep -F -x 'abc
def'
Using --label
When piping standard input into grep, as part of a pipeline, occasionally it can be useful override the file name ‘(standard input)’ with something from the pipeline. This would output each matching line instead with the name of the input file. 
$ for f in *.gz; do
> gzcat $f | grep -H --label=$f foo
> done

See environ(7) for descriptions of the following environment variables that affect the execution of grep: LANG, LC_ALL, LC_COLLATE, LC_CTYPE, LC_MESSAGES, and NLSPATH.

sed(1), sh(1), attributes(7), environ(7), largefile(7), regex(7), standards(7)

The grep utility is compliant with the IEEE Std 1003.1-2008 (“POSIX.1”) specification with the exception of -s option being the same as -q in current implementation for historic reasons. The flags [-AbBChHrRw] are extensions to that specification.

The results are unspecified if input files contain lines longer than LINE_MAX bytes or contain binary data. LINE_MAX is defined in <limits.h>.

Portable applications should use grep -E and grep -F instead of egrep and fgrep, respectively.

The grep command first appeared in Version 6 AT&T UNIX.

In the past /usr/bin/grep, /usr/bin/egrep, and /usr/bin/fgrep were separate implementations, and were not standard conforming, with standard conforming ones installed as /usr/xpg4/bin/grep, /usr/xpg4/bin/egrep, and /usr/xpg4/bin/fgrep, respectively. Now all non-conforming implementations are removed, and the ones previously found in /usr/xpg4/bin are installed in /usr/bin.

August 13, 2020 OmniOS