This tutorial will show you how to find or search files for specific text or string in linux command line using command grep .

Are you trying to find a way to search files containing a specific string of text,which also means to list the list of files which include the string you are searching.

Short answer

grep -Riw "string-to-search-here" /path-to-search-here

A real example:

grep -Riw "host" /etc

Where:

  • -R read and process all files in /etc recursively
  • -i search string case-insensitive, also will match capital HOST
  • -w matches whole word
  • /etc where to search from

Introduction

grep is a often used command which prints lines that contain a match for one or more patterns. When grep finds a match in a line, it prints the line to standard output.

synopsis :

grep [option...] [patterns] [file...]

grep only search specific files

grep --include='*.{c,txt}' -r 'string-search'  /path-to-search

This will only search through those files which have .c or .txt extensions

grep excludes files or directories

grep --exclude='*.{c,txt}' -r 'string-search'  /path-to-search

Similar to include this command will exclude files which have .c or .txt extensions

grep --exclude-dir={dir1,dir2,log*}  -r 'string-search'  /path-to-search

We can exclude some directories to speed up the searching , above example will exclude the dirs dir1/, dir2/ and all directories whose name start from log.

Grep multiple words or strings

egrep is a good choice to do this ,egrep is the same as grep -E which will Interpret PATTERN as an extended regular expression.

$ egrep 'root|nobody' /etc/passwd
root:x:0:0:root:/root:/bin/bash
nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin

Or use grep with option

grep -E 'root|nobody' /etc/passwd

select non-matching lines

Below example will grep out comments line starting with symbol # and blank line also

$ grep -v -E '^#|^$' /etc/hosts
127.0.0.1	localhost
127.0.1.1	ubuntu
::1     ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
  • -v means select non-matching contents
  • -E parse pattern as extended regular expression
  • ^# stands a comment line
  • ^$ stands a blank line

Only list the names of matching files

grep -l 'main' test-*.c

lists names of ‘test-*.c’ files in the current directory whose contents mention ‘main’.

grep -C 5 'word' message*.log

outputs 5 lines of context around each matching line.

force grep to print the name of the file

use -H option which will print the file name for each match

$ grep -H -w root /etc/passwd
/etc/passwd:root:x:0:0:root:/root:/bin/bash

Remove “Binary file matches” report

j@ubuntu:~/dir1$ grep word *
abc:hello word ....
Binary file cmd matches
j@ubuntu:~/dir1$ grep -I word *
abc:hello word ....

Option -I which equals –binary-files=without-match

grep match cross line

With the GNU grep option -z (–null-data), each input and output “line” is null-terminated.

j@ubuntu:~/dir1$ cat test.txt 
hello word hello
world
j@ubuntu:~/dir1$ grep -z 'hello[[:space:]]\+world' test.txt 
hello word hello
world
j@ubuntu:~/dir1$

Conclusion

Now we have shown you how to search text or string using command grep in Linux command line , if you still have queries please feel free to leave a comment.