Question

I have seen | and ; and & to be used to batch together multiple commands on Linux shell. What are the differences among them?

Thanks.

Answer 1

'|' is called the pipe symbol, it is used to take the output from one command and “pipe” it to another one.

e.g.,

  ls | wc -l

takes the output of the ls command and provides it to the wc -l command which counts the number of lines. It is quite common to have several pipes in a row output at various stages.

Here’s a page that talks about pipes.

The '&' is used to put a command in the background so that it can run, while you are returned to the command prompt and can continue to issue other commands.

This page has a short example of a pipe and the amperstand to put something in the background. This page talks about managing background commands. Finally, under sh/bash (and possibly shells other than csh/tcsh) '&' can be used to redirect stdout and stderr as @cdarke reminds us in a helpful comment below.

Any decent Linux/Unix tutorial would give you more information on these two.

I haven’t seen the , used with commands, though ; can be used to group several commands.

Also see @Bruno comment below for more information about using && to chain commands in bash.