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Grep searches the named FILE(s) for lines containing a match to the given PATTERN. By default, thre results printed on the screen contain the entire matching line.

Command: grep
Synopsis: grep [options...] PATTERN [file...]

Options:
Option Long option name Description
-A NUM --after-context=n Print NUM lines of trailing context after matching lines. Places a line containing -- between contiguous groups of matches.
-a --text Process a binary file as if it were text; this is equivalent to the --binary-files=text option.
-B NUM --before-context=n Print NUM lines of leading context before matching lines. Places a line containing -- between contiguous groups of matches.
-C NUM --context=n Print NUM lines of output context both before and after matching lines. Places a line containing -- between contiguous groups of matches.
-b --byte-offset Print the byte offset within the input file before each line of output.
--binary-files=TYPE If the first few bytes of a file indicate that the file contains binary data, assume that the file is of type TYPE. By default, TYPE is binary, and grep normally outputs either a one-line message saying that a binary file matches, or no message if there is no match. If TYPE is without-match, grep assumes that a binary file does not match; this is equivalent to the -I option. If TYPE is text, grep processes a binary file as if it were text; this is equivalent to the -a option. Warning: grep --binary-files=text might output binary garbage, which can have nasty side effects if the output is a terminal and if the terminal driver interprets some of it as commands.
--colour[=WHEN], --color[=WHEN] Surround the matching string with the marker find in GREP_COLOR environment variable. WHEN may be 'never', 'always', or 'auto'
-c --count Suppress normal output; instead print a count of matching lines for each input file. With the -v, --invert-match option (see below), count non-matching lines.
-D ACTION --devices=ACTION If an input file is a device, FIFO or socket, use ACTION to process it. By default, ACTION is read, which means that devices are read just as if they were ordinary files. If ACTION is skip, devices are silently skipped.
-d --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. If ACTION is skip, directories are silently skipped. If ACTION is recurse, grep reads all files under each directory, recursively; this is equivalent to the -r option.
-E --extended-regexp Interpret PATTERN as an extended regular expression (see below).
-e PATTERN --regexp=PATTERN Interpret PATTERN as a Perl regular expression.
-f FILE --file=FILE Obtain patterns from FILE, one per line. The empty file contains zero patterns, and therefore matches nothing.
-G --basic-regexp Interpret PATTERN as a basic regular expression (see below). This is the default.
-H --with-filename Print the filename for each match.
-h --no-filename Suppress the prefixing of filenames on output when multiple files are searched.
-I Process a binary file as if it did not contain matching data; this is equivalent to the --binary-files=without-match option.
-i --ignore-case Ignore case distinctions in both the PATTERN and the input files.
-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 will stop on the first match.
-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 will stop on the first match.
-m NUM --max-count=NUM Stop reading a file after NUM matching lines. If the input is standard input from a regular file, and NUM matching lines are output, grep ensures that the standard input is positioned to just after the last matching line before exiting, regardless of the presence of trailing context lines. This enables a calling process to resume a search. When grep stops after NUM matching lines, it outputs any trailing context lines. When the -c or --count option is also used, grep does not output a count greater than NUM. When the -v or --invert-match option is also used, grep stops after outputting NUM non-matching lines.
--mmap If possible, use the mmap(2) system call to read input, instead of the default read(2) system call. In some situations, --mmap yields better performance. However, --mmap can cause undefined behavior (including core dumps) if an input file shrinks while grep is operating, or if an I/O error occurs.
-n -line-number Prefix each line of output with the line number within its input file.
-o --only-matching Show only the part of a matching line that matches PATTERN.
--label=LABEL Displays input actually coming from standard input as input coming from file LABEL. This is especially useful for tools like zgrep, e.g. gzip -cd foo.gz |grep -H --label=foo something.
-I Process a binary file as if it did not contain matching data; this is equivalent to the --binary-files=without-match option.
--line-buffered Use line buffering, it can be a performance penalty.
-q --quiet, --silent Quiet; do not write anything to standard output. Exit immediately with zero status if any match is found, even if an error was detected. Also see the -s or --no- messages option.
-R, -r --recursive Read all files under each directory, recursively; this is equivalent to the -d recurse option.
--include=PATTERN Recurse in directories only searching file matching PATTERN.
--exclude=PATTERN Recurse in directories skip file matching PATTERN.
-s --no-messages Suppress error messages about nonexistent or unreadable files. Portability note: unlike GNU grep, traditional grep did not conform to POSIX.2, because traditional grep lacked a -q option and its -s option behaved like GNU grepâs -q option. Shell scripts intended to be portable to traditional grep should avoid both -q and -s and should redirect output to /dev/null instead.
-U --binary Treat the file(s) as binary. By default, under MS-DOS and MS-Windows, grep guesses the file type by looking at the contents of the first 32KB read from the file. If 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 grep to report byte offsets as if the file were Unix-style text file, i.e. with CR characters stripped off. This will produce results identical to running 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.
-V --version Print the version number of grep to standard error. This version number should be included in all bug reports.
-v --invert-match Invert the sense of matching, to select non-matching lines.
-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 charac- ters are letters, digits, and the underscore.
-x --line-regexp Select only those matches that exactly match the whole line.
-y Obsolete synonym for -i.
-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.

Examples

The Base Command

grep PATTERN [FILE] - At the base command level, grep is very simple. In the example below, we look for the pattern 'Lorem' in a file named test.txt. As you can see, it found the pattern twice and returned both lines as a result.

# grep 'Lorem' test.txt
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi convallis vehicula nisi.
Lorem ipsum dolor sit amet, consectetur adipiscing elit.

Display specific number of lines after pattern.

grep -A NUM PATTERN [FILE] - This option will display a specified number of lines (NUM) after the pattern is located in the FILE. In the example below, we use the command to display the next 2 lines after the line where the pattern 'Lorem' is found. A line displaying -- is used in between each grouping.

# grep -A 2 'Lorem' test.txt
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi convallis vehicula nisi.
Cras consequat consectetur lectus in cursus.
Ut vulputate interdum arcu, imperdiet sodales nisl adipiscing vitae.
--
Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Aliquam cursus diam nunc, nec porttitor elit gravida eu.
Donec in neque sapien. Suspendisse porta odio id fermentum placerat.
--

Display specific number of lines before pattern.

grep -B NUM PATTERN [FILE] - Much like the -A option, the -B option displays a specified number of lines prior to the pattern. In the example below, we display 2 lines prior to the line that the pattern 'Lorem' is located. Again, each instance found is separated by a line with --. Note that the first line only shows the located pattern. This is because it was found on the first line of the file.

# grep -B 2 'Lorem' test.txt
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi convallis vehicula nisi.
--
Proin feugiat turpis elit, et semper turpis pretium sit amet.
Praesent ultrices, dui consequat commodo ultricies, velit enim pulvinar libero, posuere consectetur turpis quam vel est.
Lorem ipsum dolor sit amet, consectetur adipiscing elit.
--
Phasellus non commodo erat.

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi convallis vehicula nisi.
--

Display specific number of lines before and after pattern.

grep -C NUM PATTERN [FILE] - Acting as a combination of both the -A and -B options, the -C displays a number of lines both before and after the line the pattern is located.

# grep -C 2 'Lorem' test.txt
Proin feugiat turpis elit, et semper turpis pretium sit amet.
Praesent ultrices, dui consequat commodo ultricies, velit enim pulvinar libero, posuere consectetur turpis quam vel est.
Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Aliquam cursus diam nunc, nec porttitor elit gravida eu.
Donec in neque sapien. Suspendisse porta odio id fermentum placerat.
--
Phasellus non commodo erat.

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi convallis vehicula nisi.
Cras consequat consectetur lectus in cursus.
Ut vulputate interdum arcu, imperdiet sodales nisl adipiscing vitae.
--

Display line number on which the pattern is located.

grep -n PATTERN [FILE] - Using the -n option, the line number the pattern is found will be printed at the beginning of the output.

# grep -n 'Lorem' test.txt
1:Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi convallis vehicula nisi.
21:Lorem ipsum dolor sit amet, consectetur adipiscing elit.
161:Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi convallis vehicula nisi.
181:Lorem ipsum dolor sit amet, consectetur adipiscing elit.
321:Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi convallis vehicula nisi.
341:Lorem ipsum dolor sit amet, consectetur adipiscing elit.

Display the filename in which the pattern is located.

grep -H PATTERN [FILE] - If looking through more than one file, using the -H option will cause the filename the match was located to be displayed. In our example below, we look through two files: test.txt and test2.txt. You can see the results display which file each instance was located.

# grep -n 'Lorem' test.txt test2.txt
test.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi convallis vehicula nisi.
test.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit.
test.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi convallis vehicula nisi.
test.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit.
test.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi convallis vehicula nisi.
test.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit.
test2.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi convallis vehicula nisi.Cras consequat consectetur lectus in cursus. Ut vulputate interdum arcu, imperdiet sodales nisl
test2.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit.
test2.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi convallis vehicula nisi.
test2.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit.
test2.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi convallis vehicula nisi.
test2.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit.

Search through a directory recursively.

grep -r PATTERN [DIRECTORY] - If you want to search for a pattern through one or more directories, use the -r option. Instead of a filename, place the path of the directory you want to search. For example: /home/userna5/public_html will start the search at the public_html folder for the userna5 user. You can also use a . as the directory so that the search begins in the directory you are logged into. The results will also display the filename at the beginning of each instance found, just like the -H option above.

# grep -r 'Lorem' /home/userna5/public_html
test.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi convallis vehicula nisi.
test.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit.
test.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi convallis vehicula nisi.
test.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit.
test.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi convallis vehicula nisi.
test.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit.
test2.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi convallis vehicula nisi.Cras consequat consectetur lectus in cursus. Ut vulputate interdum arcu, imperdiet sodales nisl
test2.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit.
test2.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi convallis vehicula nisi.
test2.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit.
test2.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi convallis vehicula nisi.
test2.txt:Lorem ipsum dolor sit amet, consectetur adipiscing elit.

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