The pipe

|

Pass the output of one command to the input of another

How it works

| (the pipe) connects commands: what the left one prints becomes the input of the right one. cat app.log | grep ERROR prints the log and keeps only the error lines straight away.

A chain can be as long as you like: history | grep git | tail -5 shows your last five git commands. That is how simple commands add up to the result you need: each does one job, and the pipe links them.

Syntax

<command> | <command>
<command> | <command> | <command>

Examples

• Pipe app.log into grep and keep the lines with ERROR

  cat app.log | grep ERROR

  same as: cat app.log|grep ERROR

  • cat app.log — print the file
  • | — pipe: output on the left → input on the right
  • grep ERROR — filter lines

• Show the last 20 commands from history

  history | tail -20

  same as: history | tail -n 20, history | tail -n20

  • history — command history
  • | — pass it on
  • tail -20 — last 20 lines

Related commands

• grep — Find the lines with some text in files
• > >> 2> — Output redirection. Write a command's output to a file instead of the screen
• sort — Sort lines and drop duplicates

Practise · All commands