This post explains about grep command to find multiple strings or keyword from file. In Linux or Unix like operating system, the grep command utility is widely used.

Grep is a command-line utility for searching plain-text data sets for lines matching a regular expression. Grep was originally developed for the Unix operating system, but is available today for all Unix-like systems. Its name comes from the ed command g/re/p (globally search a regular expression and print), which has the same effect: doing a global search with the regular expression and printing all matching lines. (Definition reference from Wikipedia)

Find the multiple strings or keyword in file by using grep command

To find the multiple strings or keyword in a file by using grep command,use the below given syntax

grep [options] 'keyword1|keyword2|Keyword3|keyword-N' /path/file-name

Example:

The below given is our sample file with contents

linux@tuxworld:/tmp$ cat sample.txt 
Orange
white
blue
Blue line
black
red
Red Apple
green leaves
yellow
violet
pink rose
linux@tuxworld:/tmp$

Now using grep command to find multiple keywords from file called sample.txt

linux@tuxworld:/tmp$ grep 'black|red' sample.txt 
black
red
linux@tuxworld:/tmp$

For Exact Keyword :
Use -w option for exact matching keyword ( Check man grep for this option )
With -w option, I searched only for exact keyword means case sensitive. If you have noticed, the keyword blue and Blue exist in sample.txt file

linux@tuxworld:/tmp$ grep -w 'black|red|blue' sample.txt 
blue
black
red
linux@tuxworld:/tmp$

For Non Case Sensitive Keyword :

Use -i option withe grep command to find multiple non case sensitive keywords.
In our sample.txt we have two keyword i.e Blue and blue . Now we want to search keyword with non case sensitive option. Whereas we will also search some other keyword in same grep command.

linux@tuxworld:/tmp$ grep -i 'blue|yellow|red|green' sample.txt 
blue
Blue line
red
Red Apple
green leaves
yellow
linux@tuxworld:/tmp$