A capability in Shell Programming that allows grabbing the output of a command by spawning a Subshell.
echo `ls`
echo $(ls)- Double quotes prevent wildcard replacement
- Single quotes prevent wildcard replacement, Variable Substitution, Command Substitution
$ echo Today is `date`
Today is Thu Sep 19 12:28:55 EST 2002
$ echo "Today is `date`"
Today is Thu Sep 19 12:28:55 EST 2002
$ echo 'Today is `date`'
Today is Thu Sep 19 12:28:55 EST 2002