“grep” stands for “Global Regular Expressions Print”.  The grep filter scans a file for a certain sequence of characters and shows all lines containing that sequence. Regular expression refers to the pattern that is searched inside the file.

Command

$ grep [options] pattern [file]

Options

Here are details about some options.

Option	Details
-i	Ignore case differences in patterns and input data so that characters that only differ in case will match.
-f	Obtain patterns from File, one per line.
-e	This option allows you to provide an expression. Can use numerous times.
-h	Display the matched lines, but do not display the filenames.
-c	Print out the number of matching lines in each file.
-l	Only shows a list of filenames.
-n	Show the lines that match and their line numbers.
-v	This makes all the lines that do not fit the pattern print out.
-w	Select  only  those  lines  containing  matches  that form whole words.
-o	Only print the parts of a line that match, with each part on a separate line.
-R	Read  all  files  under each directory, recursively.

Examples

• Now, let us see some examples.

grep -i linux linux_introduction.txt

grep -c Linux linux_introduction.txt

grep -w Linux linux_introduction.txt

grep -n Linux linux_introduction.txt

grep -l Linux *

grep -iR Ubuntu .