The Bourne shell can redirect a command’s standard output back to the shell’s own command line i.e., the command’s output can be used as an argument to another command, or it can store the command output in a shell variable. It can be done by enclosing a command in the back quote (`) or in braces(()).
Syntax:
Var=`command`
OR
Var=$(command)
$ PROC=`ps -ef |grep user1 $ echo $PROC root 8428 8388 0 14:20 pts/1 00:00:00 su - user1 user1 8429 8428 0 14:20 pts/1 00:00:00 -bash user1 8457 8429 0 14:20 pts/1 00:00:00 -ksh user1 8507 8457 0 14:30 pts/1 00:00:00 -ef