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| Chapter 4 The Bourne Shell and Korn Shell |

## :

    :

Null command. Returns an exit status of 0. Sometimes used as the first character in a file to denote a Bourne shell script. See example below and under case. In the Korn shell, shell variables can be placed after the : to expand them to their values.

### Example

Check whether someone is logged in:

>     if who | grep $1 > /dev/null
>     then :	# do nothing
>     	# if pattern is found
>     else echo "User $1 is not logged in"
>     fi

Reference: #!shell |  | Reference: .