grep command tutorial

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What is grep?

 grep stands for Globally search a Regular Expression and Print. Created by Ken Thompson, the author of B Programming Language. It is a command-line utility to search a particular string in the files.

Usage 1: Search a particular word in file

 To search a particular word in a file.

$ grep <word> <file to search>

Eg. grep hello words.txt

The above command searches for word "hello" in the file "words.txt" and prints the matching lines in which the word "hello" is present in the file .

The above command by default performs case sensitive search, this means if there is "Hello" present in the words.txt file it won't be detected by the search.

Usage 2: Case Insensitive word search in file

 $grep -i <word> <file to search>

Eg: grep -i hello words.txt

The above command performs case insensitive search and gives you "hello"  "Hello" or other variants in the search.

Usage 3: Count the number of times a word repeats

 $grep -c <word> <file to search>

Eg: grep -c hello words.txt

Will print the number of times the word hello is present in the words.txt file. This command is similar to $grep hello words.txt | wc -l

You can also combine the insensitive search also in this.
Eg: grep -i -c hello words.txt

Will gives number of times the word hello is present and the search is case insensitive.


Usage 4: Print Line numbers in the search

 $grep -n <word> <file to search>

Eg: grep -n hello words.txt

will print the line numbers along with the matching lines present in the words.txt file

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