grep(1)

NAME

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

SYNOPSIS

Plain call with pattern

grep [-E|-F] [-c|-l|-q] [-bhinsvwx] pattern [file ...]

Call with (multiple) -e pattern

grep [-E|-F] [-c|-l|-q] [-bhinsvwx] -e pattern... [-e pattern] ... [file ...]

Call with -f file

grep [-E|-F] [-c|-l|-q] [-bhinsvwx] [-f pattern_file] [file ...]

Obsolescent:

egrep [-cefilnsv] [expression] [file ...]

fgrep [-cefilnsvx] [strings] [file ...]

DESCRIPTION

The grep command searches the input text files (standard input default) for lines matching a pattern. Normally, each line found is copied to the standard output. grep supports the Basic Regular Expression syntax (see regexp(5)). The -E option (egrep) supports Extended Regular Expression (ERE) syntax (see regexp(5)). The -F option (fgrep) searches for fixed strings using the fast Boyer-Moore string searching algorithm. The -E and -F options treat newlines embedded in the pattern as alternation characters. A null expression or string matches every line.

The forms egrep and fgrep are maintained for backward compatibility. The use of the -E and -F options is recommended for portability.

Options

-E: Extended regular expressions. Each pattern specified is a sequence of one or more EREs. The EREs can be separated by newline characters or given in separate -e expression options. A pattern matches an input line if any ERE in the sequence matches the contents of the input line without its trailing newline character. The same functionality is obtained by using egrep.
-F: Fixed strings. Each pattern specified is a sequence of one or more strings. Strings can be separated by newline characters or given in separate -e expression options. A pattern matches an input line if the line contains any of the strings in the sequence. The same functionality is obtained by using fgrep.
-b: Each line is preceded by the block number on which it was found. This is useful in locating disk block numbers by context. Block numbers are calculated by dividing by 512 the number of bytes that have been read from the file and rounding down the result.
-c: Only a count of matching lines is printed.
-e expression: Same as a simple expression argument, but useful when the expression begins with a hyphen (-). Multiple -e options can be used to specify multiple patterns; an input line is selected if it matches any of the specified patterns.
-f pattern_file: The regular expression (grep and grep -E) or strings list (grep -F) is taken from the pattern_file.
-h: Suppress printing of filenames when searching multiple files.
-i: Ignore uppercase/lowercase distinctions during comparisons.
-l: Only the names of files with matching lines are listed (once), separated by newlines. If standard input is searched, a path name of (standard input) will be written, in the POSIX locale. In other locales, (standard input) may be replaced by something more appropriate in those locales.
-n: Each line is preceded by its relative line number in the file starting at 1. The line number is reset for each file searched. This option is ignored if -c, -b, -l, or -q is specified.
-q: (Quiet) Do not write anything to the standard output, regardless of matching lines. Exit with zero status upon finding the first matching line. Overrides any options that would produce output.
-s: Error messages produced for nonexistent or unreadable files are suppressed.
-v: All lines but those matching are printed.
-w: Select only those lines containing matches that form whole words. The test is that the matching substring must either be at the beginning of the line, or preceded by a non-word constituent character. Similarly, it must be either at the end of the line or followed by a non-word constituent character. Word-constituent characters are letters, digits, and the underscore.
-x: (eXact) Matches are recognized only when the entire input line matches the fixed string or regular expression.

The file name is output in all the cases in which output is generated if there are more than one input file, unless the -h option is specified. Care should be taken when using the characters $, *, [, ^, |, (, ), and \ in expression, because they are also meaningful to the shell. It is safest to enclose the entire expression argument in single quotes ('...').

EXTERNAL INFLUENCES

Environment Variables

LANG determines the locale to use for the locale categories when both LC_ALL and the corresponding environment variable (beginning with LC_) do not specify a locale. If LANG is not specified or is set to the empty string, a default of C (see lang(5)) is used.

LC_ALL determines the locale to use to override any values for locale categories specified by the settings of LANG or any environment variables beginning with LC_.

LC_COLLATE determines the collating sequence used in evaluating regular expressions.

LC_CTYPE determines the interpretation of text as single byte and/or multi-byte characters, the classification of characters as letters, the case information for the -i option, and the characters matched by character class expressions in regular expressions.

LC_MESSAGES determines the language in which messages are displayed.

If any internationalization variable contains an invalid setting, the commands behave as if all internationalization variables are set to C. See environ(5).

International Code Set Support

Single-byte and multi-byte character code sets are supported.

RETURN VALUE

Upon completion, grep returns one of the following values:

0: One or more matches found.
1: No match found.
2: Syntax error or inaccessible file (even if matches were found).

EXAMPLES

In the POSIX shell ( sh(1)) the following example searches two files, finding all lines containing occurrences of any of four strings:

grep -F 'if 
then 
else 
fi' file1 file2

Note that the single quotes are necessary to tell grep -F when the strings have ended and the file names have begun.

For the C shell (see csh(1)) the following command can be used:

grep -F 'if\  then\  else\ fi'  file1  file2

To search a file named address containing the following entries:

Ken   112 Warring St.  Apt. A 
Judy  387 Bowditch  Apt. 12 
Ann   429 Sixth St. 

the command:

grep Judy address 

prints:

Judy  387 Bowditch  Apt. 12 

To search a file for lines that contain either a Dec or Nov, use either of the following commands:

grep -E '[Dd]ec|[Nn]ov' file
egrep -i 'dec|nov' file

Search all files in the current directory for the string xyz:

grep xyz * 

Search all files in the current directory subtree for the string xyz, and ensure that no error occurs due to file name expansion exceeding system argument list limits:

find . -type f -print |xargs grep xyz 

The previous example does not print the name of files where string xyz appears. To force grep to print file names, add a second argument to the grep command portion of the command line:

find . -type f -print |xargs grep xyz /dev/null 

In this form, the first file name is that produced by find, and the second file name is the null file.

WARNINGS

(XPG4 only.) If the -q option is specified, the exit status will be zero if an input line is selected, even if an error was detected. Otherwise, default actions will be performed.

If the -w option is specified with non-word constituent characters, then the output is unexpected.

STANDARDS CONFORMANCE

grep: SVID2, SVID3, XPG2, XPG3, XPG4, POSIX.2

egrep: SVID2, SVID3, XPG2, XPG3, XPG4, POSIX.2

fgrep: SVID2, SVID3, XPG2, XPG3, XPG4, POSIX.2