Pipes and Redirection

Pipes

Pipes are used to redirect output from one command into the input of another. When a command outputs text to the screen, that is called standard out (stdout). A pipe will redirect the standard output of a process to the standard in (stdin) of another program.

$ ls | wc -l

The above example pipes the output of ls to the input of wc -l.

wc stands for word count and -l tells wc to count lines instead of characters. This command will output the number of files in the directory.

Redirect Input and Output

A program’s output can be redirected to a file instead of stdout using >.

$ ls > list-of-files.txt

The content of a file can be sent as stdin to a program with <.

$ wc -l < list-of-files.txt

> will overwrite the contents of an existing file. Use >> to append to a file.

$ some-command > logfile

$ other-command >> logfile