The feature has since been adopted in other programming languages as well, including Perl, PHP, Ruby and Microsoft's Powershell under Windows.
Shells typically implement command substitution by creating a child process to run the first command with its standard output piped back to the shell, which reads that output, parsing it into words separated by whitespace.
This C shell example shows how one might search for all the C files containing the string malloc using fgrep and then edit any that are found using the vi editor.
The syntactical notation shown here, ` ... `, using backquotes as delimiters, is the original style and is supported by all the common Unix shells.
Hamilton C shell solved this with a double backquote notation, `` ... ``, that parses into words only at line breaks.