How do I search the input text files for lines matching given words or strings under UNIX operating systems?

To search for a particular word or string in a file, use the grep command.

Syntax

The basic syntax of the grep command is as follows:

grep string fileName
grep word fileName
grep "word1 word2" fileName

Examples

For example, to find Vivek Gite’s email id, type grep, and the file containing the information:

grep Vivek users.txt
grep "Vivek Gite" users.txt
grep "Gite" users.txt

Sample outputs:

Vivek Gite    123-455-676 vivek@nixcraft.com

To search word apple in all text file (*.txt) enter:

grep apple *.txt

You can also search for lines without a certain words. For example, display all line that do not contain the word “usb”

grep -v "usb" *

See more grep command examples here.