Learn grep command by examples

grep command can be used to search the named input FILEs, or standard input if no files are named, for lines containing a match to the given PATTERN. By default, grep prints the matching lines.

Example usages.

Suppose you have these files:

file.txt	file2.txt
word1 word2 word3 hello world! word5 word6	word1 word2 hello friend! word4 word5 word6

• Print the lines containing "hello" from file.txt:

$ grep 'hello' file.txt

hello world!

• Search in multiple files:

$ grep 'hello' file.txt file2.txt

file.txt:hello world!

file2.txt:hello friend!

• For multiple strings:

$ grep 'hello world' file.txt

hello world!

• Alternative commands:

$ cat file.txt | grep 'hello'

$ grep -i 'hello' file.txt

• Search recursively for a string inside files in directory:

$ grep -r "hello" /home/abc

/home/file.txt:hello world!

• Same result, without showing file name:

$ grep -h -R "hello" /home/abc

hello world!

• Print the number of lines in file, containing the string:

$ grep -c 'hello' file.txt

1

• Print also the line number in file, where the string is found:

$ grep -n 'hello' file.txt

4:hello world!

• Invert match: print only those lines that do not contain the given word:

$ grep -v 'hello' file.txt

word1

word2

word3

word5

word6

• List all the files with .txt extension containing the string:

$ grep -l 'hello' *.txt

file.txt

• Search exactly for a string inside a file:

$ grep -x 'hello world' file.txt

(give no results)

$ grep -x 'hello world!' file.txt

hello world! 

• Use colors to highlight matches:

$ grep --color hello file.txt

hello world!