grep by Example

Syntax: grep 'word' file1 file2 file3

To find all lines containing behnam:

$ grep -i behnam /etc/passwd

To search recursively i.e. read all files under /etc:

$ grep -r 192.168.1.5 /etc/

To search only behnam not behnamp:

$ grep -w behnam test.txt

To search 2 different words:

$ egrep -w behnam|behdad test.txt

To report the number of times that the pattern has been matched:

$ grep -c behnam test.txt

To precede each line of output with the number of the line in the file:

$ grep -n root /etc/passwd

Tp print all lines that do not contain behnam:

$ grep -v behnam test.txt

To find out how many lines does not match the pattern:

$ grep -v -c behnam test.txt

To display lines starting with the string "root"

$ grep ^root /etc/passwd

To filter the name of the hard disk partitions in dmesg output: 

$ dmesg | egrep "(s|h)d[a-z][1-9]"

Note: The above example does not work with grep and as you see we used egrep instead. egrep is nothing but grep -E which switches grep into a special mode so that the expression is evaluated as an Extended Regular Expression as opposed to its normal pattern matching.

To list text files whose contents mention behnam:

$ grep -l behnam *.txt

To display output in colors:

$ grep --color root /etc/passwd

To search a string in a Gzip compressed file:

$ zgrep –i behnam test.tar.gz

To see which accounts have no shell assigned

$ grep :$ /etc/passwd

To display all words starting with b and ending in m:

$ grep '\<b.*m\>' test.txt

To display the lines which does not match 2 or more patterns: 

$ grep -v -e "pattern 1" -e "pattern 2"

To show the position of match:

$ grep -o -b root /etc/passwd