grep
- Details
The grep command searches the given input FILEs for lines containing a match or a text string.
grep command syntax
The syntax is:
grep -options "text string to search” directory-path
OR
grep [option] "text string to search” directory-path
OR
grep -r "text string to search” directory-path
OR
grep -r -H "text string to search” directory-path
OR
egrep -R "word-1|word-2” directory-path
OR
egrep -w -R "word-1|word-2” directory-path
Examples
Search only certain file types. For example only php files:
$ grep -r --include=*.php "search string" /path/to/dir
Task: Search all subdirectories recursively
You can search for a text string all files under each directory, recursively with -r option:
$ grep -r "redeem reward" /home/tom/
OR
$ grep -R "redeem reward" /home/tom/
Task: Only display filenames
By default, the grep command prints the matching lines. You can pass -H option to print the filename for each match:
$ grep -H -r "redeem reward" /home/tom
Sample outputs:
filename.txt: redeem reward foobar.txt: redeem reward ...
To just display the filename use the cut command as follows:
$ grep -H -R vivek /etc/* | cut -d: -f1
Sample outputs:
filename.txt foobar.txt ...
Task: Suppress file names
The grep command shows output on a separate line, and it is preceded by the name of the file in which it was found in the case of multiple files. You can pass the -h option to suppress inclusion of the file names in the output:
$ grep -h -R 'main()' ~/projects/*.c
Task: Display only words
You can select only those lines containing matches that form whole words using the -w option. In this example, search for word 'getMyData()' only in ~/projects/ dirctory:
$ grep -w -R 'getMyData()' ~/projects/
Task: Search for two or more words
Use the egrep command as follows:
$ egrep -w -R 'word1|word2' ~/projects/
Task: Hide warning spam
grep command generate error message as follows due to permission and other issues:
No such file or directory
No such device or address
Permission denied
To hide all errors or warning message spam generated by the grep command, append 2>/dev/null to grep command. This will send and hide unwanted output to /dev/null device:
$ grep -w -R 'getMyData()' ~/projects/ 2>/dev/null
Task: Display matched text in color
Pass the --color option to the grep command display matched text/words in color on the terminal:
grep --color 'word' file grep --color -R 'word' /path/to/dir grep --color -R "192.168.1.5" /etc/ grep --color -R -h "192.168.1.5" /etc/ grep --color -R -h "192.168.1.5" /etc/ 2>/dev/null
Sample outputs:
Task: Ignore case
Our final example ignore case distinctions in both the search PATTERN and the input files:
grep -i -R 'word' /path/to/dir
grep -i -r 'income tax' ~/accounting/
Example: grep -i 'hello world' menu.h main.c
Pattern selection and interpretation:
-E, --extended-regexp PATTERN is an extended regular expression
-F, --fixed-strings PATTERN is a set of newline-separated strings
-G, --basic-regexp PATTERN is a basic regular expression (default)
-P, --perl-regexp PATTERN is a Perl regular expression
-e, --regexp=PATTERN use PATTERN for matching
-f, --file=FILE obtain PATTERN from FILE
-i, --ignore-case ignore case distinctions
-w, --word-regexp force PATTERN to match only whole words
-x, --line-regexp force PATTERN to match only whole lines
-z, --null-data a data line ends in 0 byte, not newline
Miscellaneous:
-s, --no-messages suppress error messages
-v, --invert-match select non-matching lines
-V, --version display version information and exit
--help display this help text and exit
Output control:
-m, --max-count=NUM stop after NUM selected lines
-b, --byte-offset print the byte offset with output lines
-n, --line-number print line number with output lines
--line-buffered flush output on every line
-H, --with-filename print file name with output lines
-h, --no-filename suppress the file name prefix on output
--label=LABEL use LABEL as the standard input file name prefix
-o, --only-matching show only the part of a line matching PATTERN
-q, --quiet, --silent suppress all normal output
--binary-files=TYPE assume that binary files are TYPE;
TYPE is 'binary', 'text', or 'without-match'
-a, --text equivalent to --binary-files=text
-I equivalent to --binary-files=without-match
-d, --directories=ACTION how to handle directories;
ACTION is 'read', 'recurse', or 'skip'
-D, --devices=ACTION how to handle devices, FIFOs and sockets;
ACTION is 'read' or 'skip'
-r, --recursive like --directories=recurse
-R, --dereference-recursive likewise, but follow all symlinks
--include=FILE_PATTERN search only files that match FILE_PATTERN
--exclude=FILE_PATTERN skip files and directories matching FILE_PATTERN
--exclude-from=FILE skip files matching any file pattern from FILE
--exclude-dir=PATTERN directories that match PATTERN will be skipped.
-L, --files-without-match print only names of FILEs with no selected lines
-l, --files-with-matches print only names of FILEs with selected lines
-c, --count print only a count of selected lines per FILE
-T, --initial-tab make tabs line up (if needed)
-Z, --null print 0 byte after FILE name