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Grep Command In Linux

The 'grep' command stands for "global regular expression print". grep command filters the content of a file which makes our search simple.

Grep With Pipe

The 'grep' command is often used with pipe (|).

Syntax:

command | grep <searchWord>

Example:

cat marks.txt | grep 9

Look at the above snapshot, grep command filters all the data containing '9'.

Grep Without Pipe

It may be used without pipe as well.

Syntax:

grep <searchWord> <file name>

Example:

grep 9 marks.txt

Look at the above snapshot, the grep command accomplish the same thing as the previous example but without pipe.

Grep Options

grep -vM: The 'grep -v' command reveals lines not matching the provided term.

Syntax:

grep -v <searchWord> <fileName>

Example:

grep -v 9 marks.txt

grep -v 9 marks.txt

Look at the preceding snapshot, program "grep -v 9 marks.txt" reveals lines that don't include our search phrase '9'.

Grep -i

The 'grep -i' command filters output in a case-insensitive way.

Syntax:

grep -i <searchWord> <fileName>

Example:

grep -i red exm.txt

Look at the preceding snapshot, program "grep -i red exm.txt" reveals all lines containing 'red' whether in upper case or lower case.

grep -A/ grep -B/ grep -C

grep -A command is used to display the line after the result.

grep -B command is used to display the line preceding the result.

grep -C command is used to display the line after and line before the result.

You may use (A1, A2, A3.....)(B1, B2, B3....)(C1, C2, C3....) to show any number of lines.

Syntax:

grep -A<lineNumber> <searchWord> <fileName>

grep -B<lineNumber> <searchWord> <fileName>

grep -C<lineNumber> <searchWord> <fileName>

Example:

grep -A1 yellow exm.txt

grep -B1 yellow exm.txt

grep -C1 yellow exm.txt

Look at the above snapshot, command "grep -A1 yellow exm.txt" shows searched line with next following line, the command "grep -B1 yellow exm.txt" displays searched line with one previous line and command "grep -C1 yellow exm.txt" displays searched line with one preceding and succeeding line.