Command substitution

This article provides insufficient context for those unfamiliar with the subject. Please help improve the article by providing more context for the reader. (March 2023) (Learn how and when to remove this message)

In computing, command substitution is a facility that allows a command to be run and its output to be pasted back on the command line as arguments to another command. Command substitution first appeared in the Bourne shell,^[1] introduced with Version 7 Unix in 1979, and has remained a characteristic of all later Unix shells. The feature has since been adopted in other programming languages as well, including Perl, PHP, Ruby and Microsoft's Powershell under Windows. It also appears in Microsoft's CMD.EXE in the FOR command and the ( ) command.