Bash Pipes

What is a Pipe?

A pipe (|) sends the output of one command directly into the next command.

This lets you combine small, simple commands to do bigger jobs. It is one of the most useful features of Bash.

All examples below use this file, fruits.txt:

apple
banana
apple
cherry
banana
apple

Your First Pipe

Here, cat prints the file, and the pipe sends that output to head -n 2, which keeps the first two lines:

cat fruits.txt | head -n 2
apple
banana

Chain Several Commands

You can connect as many commands as you like. Each one works on the output of the one before it.

This sorts the fruits, then uniq removes the duplicate lines:

sort fruits.txt | uniq
apple
banana
cherry

Add -c to uniq to count each line, then sort by that count, highest first:

sort fruits.txt | uniq -c | sort -rn
      3 apple
      2 banana
      1 cherry

Count Results with a Pipe

Piping into wc -l counts the lines of any output. This counts how many lines contain "apple":

grep apple fruits.txt | wc -l
3

Save and Show at the Same Time (tee)

The tee command writes its input to a file and passes it on to the screen (or the next command):

sort fruits.txt | uniq | tee unique.txt
apple
banana
cherry
cat unique.txt
apple
banana
cherry

Pipes vs. Redirection

A pipe (|) connects a command to another command.

Redirection (>) connects a command to a file. See Bash Redirection.