Filters

• If a Linux command accepts its input data from the standard input and produces its output (result) on standard output is known as a filter.
• Filters usually works with Linux pipes.

Syntax

The syntax is:

command1 | command2 
command1 file.txt | command2
command1 args < input.txt | command2

Where,

• command2 is a filter command.

Example

In this example, the grep command act as a filter (it will filter out name vivek from its input):

cut -d: -f1 /etc/passwd | sort | uniq | grep vivek

Filter ps command output using the grep command:

ps aux | grep php-cgi

Consider the following example:

sort < sname | uniq > u_sname

The uniq command is filter, which takes its input from the sort command and passes output as input to uniq command; Then uniq command output is redirected to "u_sname" file. The grep command is considered as one of most popular filter under Linux and UNIX like operating systems.

Commonly used filter commands

• awk
• cut
• grep
• gzip
• head
• paste
• perl
• sed
• sort
• split
• strings
• tac
• tail
• tee
• tr
• uniq
• wc