grep

This command finds files for a pattern and prints all lines which holds that pattern.

Syntax

grep [options] pattern  filename

If there is no file specified, grep suppose standard input. Usually, every line found is copied to standard output. The file name is printed before each line found if there is more than one input file.

The file is searched line through line for the pattern. Every line which holds the pattern is displayed on the terminal. The pattern which is found for in the file is known as a regular expression.