Search file(s) for specific text.
SYNTAX
grep "Search String" [filename]
grep [-e pattern] [file…]
grep [-f file] [file…]
A simple example:
$grep “Needle in a Haystack” /etc/*
OPTIONS
-A NUM
–after-context=NUM
(GNU Extension)
Print NUM lines of trailing context after matching lines.
-a
–text
(GNU Extension)
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.
-B NUM
–before-context=NUM
(GNU Extension)
Print NUM lines of leading context before matching lines.
-b
–byte-offset
(GNU Extension)
Print the byte offset within the input file before each line of
output. When &qt;grep&qt;&qt; runs on MS-DOS or MS-Windows, the printed
byte offsets depend on whether the &qt;-u&qt;&qt; (&qt;–unix-byte-offsets&qt;&qt;)
option is used; see below.
-C NUM
–context=[NUM]
(GNU Extension)
Print NUM lines (default 2) of output context.
&qt;-c&qt;&qt;
&qt;–count&qt;&qt;
Suppress normal output; instead print a count of matching lines
for each input file. With the &qt;-v&qt;&qt;, &qt;–invert-match&qt;&qt; option,
count non-matching lines.
-d ACTION
–directories=ACTION
(GNU Extension)
If an input file is a directory, use ACTION to process it. By
default, ACTION is &qt;read&qt;&qt;, which means that directories are read
just as if they were ordinary files (some operating systems and
filesystems disallow this, and will cause &qt;grep&qt;&qt; to print error
messages for every directory). If ACTION is &qt;skip&qt;&qt;, directories
are silently skipped. If ACTION is &qt;recurse&qt;&qt;, &qt;grep&qt;&qt; reads all
files under each directory, recursively; this is equivalent to the
&qt;-r&qt;&qt; option.
&qt;-e PATTERN&qt;&qt;
&qt;–regexp=PATTERN&qt;&qt;
Use PATTERN as the pattern; useful to protect patterns beginning
with a &qt;-&qt;&qt;.
&qt;-f FILE&qt;&qt;
&qt;–file=FILE&qt;&qt;
Obtain patterns from FILE, one per line. The empty file contains
zero patterns, and therefore matches nothing.
-H
–with-filename
(GNU Extension)
Print the filename for each match.
-h
–no-filename
(GNU Extension)
Suppress the prefixing of filenames on output when multiple files
are searched.
–help
(GNU Extension)
Print a usage message briefly summarizing these command-line
options and the bug-reporting address, then exit.
&qt;-i&qt;&qt;
&qt;–ignore-case&qt;&qt;
Ignore case distinctions in both the pattern and the input files.
-L
–files-without-match
(GNU Extension)
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.
&qt;-l&qt;&qt;
&qt;–files-with-matches&qt;&qt;
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.
–mmap
(GNU Extension)
If possible, ue the &qt;mmap&qt;&qt; system call to read input, instead of
the default &qt;read&qt;&qt; system call. In some situations, &qt;–mmap&qt;&qt;
yields better performance. However, &qt;–mmap&qt;&qt; can cause undefined
behavior (including core dumps) if an input file shrinks while
&qt;grep&qt;&qt; is operating, or if an I/O error occurs.
&qt;-n&qt;&qt;
&qt;–line-number&qt;&qt;
Prefix each line of output with the line number within its input
file.
-NUM
(GNU Extension)
Same as &qt;–context=NUM&qt;&qt; lines of leading and trailing context.
However, grep will never print any given line more than once.
&qt;-q&qt;&qt;
&qt;–quiet&qt;&qt;
&qt;–silent&qt;&qt;
Quiet; suppress normal output. The scanning of every file will
stop on the first match. Also see the &qt;-s&qt;&qt; or &qt;–no-messages&qt;&qt;
option.
-r
–recursive
(GNU Extension)
For each directory mentioned in the command line, read and process
all files in that directory, recursively. This is the same as the
&qt;-d recurse&qt;&qt; option.
&qt;-s&qt;&qt;
&qt;–no-messages&qt;&qt;
Suppress error messages about nonexistent or unreadable files.
Portability note: unlike GNU &qt;grep&qt;&qt;, traditional &qt;grep&qt;&qt; did not
conform to POSIX.2, because traditional &qt;grep&qt;&qt; lacked a &qt;-q&qt;&qt;
option and its &qt;-s&qt;&qt; option behaved like GNU &qt;grep&qt;s &qt;-q&qt;&qt; option.
Shell scripts intended to be portable to traditional &qt;grep&qt;&qt; should
avoid both &qt;-q&qt;&qt; and &qt;-s&qt;&qt; and should redirect output to &qt;/dev/null&qt;&qt;
instead.
-U
–binary
(GNU Extension)
Treat the file(s) as binary. By default, under MS-DOS and
MS-Windows, &qt;grep&qt;&qt; guesses the file type by looking at the
contents of the first 32kB read from the file. If &qt;grep&qt;&qt; decides
the file is a text file, it strips the &qt;CR&qt;&qt; characters from the
original file contents (to make regular expressions with &qt;^&qt;&qt; and
&qt;$&qt;&qt; work correctly). Specifying &qt;-U&qt;&qt; overrules this guesswork,
causing all files to be read and passed to the matching mechanism
verbatim; if the file is a text file with &qt;CR/LF&qt;&qt; 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
(GNU Extension)
Report Unix-style byte offsets. This switch causes &qt;grep&qt;&qt; to
report byte offsets as if the file were Unix style text file,
i.e., the byte offsets ignore the &qt;CR&qt;&qt; characters which were
stripped. This will produce results identical to running &qt;grep&qt;&qt; on
a Unix machine. This option has no effect unless &qt;-b&qt;&qt; option is
also used; it has no effect on platforms other than MS-DOS and
MS-Windows.
&qt;-v&qt;&qt;
&qt;–invert-match&qt;&qt;
Invert the sense of matching, to select non-matching lines.
-V
–version
(GNU Extension)
Print the version number of &qt;grep&qt;&qt; to the standard output stream.
This version number should be included in all bug reports.
-w
–word-regexp
(GNU Extension)
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.
&qt;-x&qt;&qt;
&qt;–line-regexp&qt;&qt;
Select only those matches that exactly match the whole line.
-Z
–null
(GNU Extension)
Output a zero byte (the ASCII &qt;NUL&qt;&qt; character) instead of the
character that normally follows a file name. For example, &qt;grep
-lZ&qt;&qt; 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 &qt;find
-print0&qt;&qt;, &qt;perl -0&qt;&qt;, &qt;sort -z&qt;&qt;, and &qt;xargs -0&qt;&qt; to process
arbitrary file names, even those that contain newline characters.
-z
–null-data
(GNU Extension)
Treat the input as a set of lines, each terminated by a zero byte
(the ASCII &qt;NUL&qt;&qt; character) instead of a newline. Like the &qt;-Z&qt;&qt;
or &qt;–null&qt;&qt; option, this option can be used with commands like
&qt;sort -z&qt;&qt; to process arbitrary file names.
Environment variables
Grep&qt;&qt;s behavior can be affected by setting the following environment variables
GREP_OPTIONS – default options
LANG – language for messages
POSIXLY_CORRECT – Posix behaviour
_N_GNU_nonoption_argv_flags_ – ignore an operand
see &qt;info&qt;&qt; for more on these
Grep stands for: Global Regular Expression Print.
Diagnostics
Normally, exit status is 0 if matches were found, and 1 if no matches were found (the &qt;-v&qt;&qt; option inverts the sense of the exit status).
Exit status is 2 if there were syntax errors in the pattern, inaccessible input files, or other system errors.