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Invoking @command{grep}

@command{grep} comes with a rich set of options from POSIX.2 and GNU extensions.

`-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.

`-e pattern'

`--regexp=pattern'

Use pattern as the pattern; useful to protect patterns beginning with a `-'.

`-f file'

`--file=file'

Obtain patterns from file, one per line. The empty file contains zero patterns, and therefore matches nothing.

`-i'

`--ignore-case'

Ignore case distinctions in both the pattern and the input files.

`-l'

`--files-with-matches'

Suppress normal output; instead print the name of each input file from which output would normally have been printed. The scanning of every file will stop on the first match.

`-n'

`--line-number'

Prefix each line of output with the line number within its input file.

`-q'

`--quiet'

`--silent'

Quiet; suppress normal output. The scanning of every file will stop on the first match. Also see the `-s' or `--no-messages' option.

`-s'

`--no-messages'

Suppress error messages about nonexistent or unreadable files. Portability note: unlike GNU @command{grep}, traditional @command{grep} did not conform to POSIX.2, because traditional @command{grep} lacked a `-q' option and its `-s' option behaved like GNU @command{grep}'s `-q' option. Shell scripts intended to be portable to traditional @command{grep} should avoid both `-q' and `-s' and should redirect output to `/dev/null' instead.

`-v'

`--invert-match'

Invert the sense of matching, to select non-matching lines.

`-x'

`--line-regexp'

Select only those matches that exactly match the whole line.

GNU Extensions

`-A num'

`--after-context=num'

Print num lines of trailing context after matching lines.

`-B num'

`--before-context=num'

Print num lines of leading context before matching lines.

`-C num'

`--context=[num]'

Print num lines (default 2) of output context.

`-num'

Same as `--context=num' lines of leading and trailing context. However, grep will never print any given line more than once.

`-V'

`--version'

Print the version number of @command{grep} to the standard output stream. This version number should be included in all bug reports.

`--help'

Print a usage message briefly summarizing these command-line options and the bug-reporting address, then exit.

`-b'

`--byte-offset'

Print the byte offset within the input file before each line of output. When @command{grep} runs on MS-DOS or MS-Windows, the printed byte offsets depend on whether the `-u' (`--unix-byte-offsets') option is used; see below.

`-d action'

`--directories=action'

If an input file is a directory, use action to process it. By default, action is `read', which means that directories are read just as if they were ordinary files (some operating systems and filesystems disallow this, and will cause @command{grep} to print error messages for every directory). If action is `skip', directories are silently skipped. If action is `recurse', @command{grep} reads all files under each directory, recursively; this is equivalent to the `-r' option.

`-H'

`--with-filename'

Print the filename for each match.

`-h'

`--no-filename'

Suppress the prefixing of filenames on output when multiple files are searched.

`-L'

`--files-without-match'

Suppress normal output; instead print the name of each input file from which no output would normally have been printed. The scanning of every file will stop on the first match.

`-a'

`--text'

Do not suppress output lines that contain binary data. Normally, if the first few bytes of a file indicate that the file contains binary data, grep outputs only a message saying that the file matches the pattern. This option causes grep to act as if the file is a text file, even if it would otherwise be treated as binary. Warning: the result might be binary garbage printed to the terminal, which can have nasty side-effects if the terminal driver interprets some of it as commands.

`-w'

`--word-regexp'

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.

`-r'

`--recursive'

For each directory mentioned in the command line, read and process all files in that directory, recursively. This is the same as the `-d recurse' option.

`-y'

Obsolete synonym for `-i'.

`-U'

`--binary'

Treat the file(s) as binary. By default, under MS-DOS and MS-Windows, @command{grep} guesses the file type by looking at the contents of the first 32kB read from the file. If @command{grep} decides the file is a text file, it strips the CR characters from the original file contents (to make regular expressions with ^ and $ work correctly). Specifying `-U' overrules this guesswork, causing all files to be read and passed to the matching mechanism verbatim; if the file is a text file with CR/LF pairs at the end of each line, this will cause some regular expressions to fail. This option has no effect on platforms other than MS-DOS and MS-Windows.

`-u'

`--unix-byte-offsets'

Report Unix-style byte offsets. This switch causes @command{grep} to report byte offsets as if the file were Unix style text file, i.e., the byte offsets ignore the CR characters which were stripped. This will produce results identical to running @command{grep} on a Unix machine. This option has no effect unless `-b' option is also used; it has no effect on platforms other than MS-DOS and MS-Windows.

`--mmap'

If possible, use the mmap system call to read input, instead of the default read system call. In some situations, `--mmap' yields better performance. However, `--mmap' can cause undefined behavior (including core dumps) if an input file shrinks while @command{grep} is operating, or if an I/O error occurs.

`-Z'

`--null'

Output a zero byte (the ASCII NUL character) instead of the character that normally follows a file name. For example, `grep -lZ' outputs a zero byte after each file name instead of the usual newline. This option makes the output unambiguous, even in the presence of file names containing unusual characters like newlines. This option can be used with commands like `find -print0', `perl -0', `sort -z', and `xargs -0' to process arbitrary file names, even those that contain newline characters.

`-z'

`--null-data'

Treat the input as a set of lines, each terminated by a zero byte (the ASCII NUL character) instead of a newline. Like the `-Z' or `--null' option, this option can be used with commands like `sort -z' to process arbitrary file names.

Several additional options control which variant of the @command{grep} matching engine is used. See section @command{grep} programs.

Environment Variables

Grep's behavior is affected by the following environment variables.

GREP_OPTIONS

This variable specifies default options to be placed in front of any explicit options. For example, if GREP_OPTIONS is `--text --directories=skip', @command{grep} behaves as if the two options `--text' and `--directories=skip' had been specified before any explicit options. Option specifications are separated by whitespace. A backslash escapes the next character, so it can be used to specify an option containing whitespace or a backslash.

LC_ALL

LC_MESSAGES

LANG

These variables specify the LC_MESSAGES locale, which determines the language that @command{grep} uses for messages. The locale is determined by the first of these variables that is set. American English is used if none of these environment variables are set, or if the message catalog is not installed, or if @command{grep} was not compiled with national language support (NLS).

LC_ALL

LC_CTYPE

LANG

These variables specify the LC_CTYPE locale, which determines the type of characters, e.g., which characters are whitespace. The locale is determined by the first of these variables that is set. The POSIX locale is used if none of these environment variables are set, or if the locale catalog is not installed, or if @command{grep} was not compiled with national language support (NLS).

POSIXLY_CORRECT

If set, @command{grep} behaves as POSIX.2 requires; otherwise, @command{grep} behaves more like other GNU programs. POSIX.2 requires that options that follow file names must be treated as file names; by default, such options are permuted to the front of the operand list and are treated as options. Also, POSIX.2 requires that unrecognized options be diagnosed as "illegal", but since they are not really against the law the default is to diagnose them as "invalid". POSIXLY_CORRECT also disables _N_GNU_nonoption_argv_flags_, described below.

_N_GNU_nonoption_argv_flags_

(Here N is @command{grep}'s numeric process ID.) If the ith character of this environment variable's value is `1', do not consider the ith operand of @command{grep} to be an option, even if it appears to be one. A shell can put this variable in the environment for each command it runs, specifying which operands are the results of file name wildcard expansion and therefore should not be treated as options. This behavior is available only with the GNU C library, and only when POSIXLY_CORRECT is not set.

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