Question

5

Add "not" to if statement in shell script

rated 0 times [ 5] [ 0] / answers: 1 / hits: 5034 / 2 Years ago, mon, february 21, 2022, 9:43:21

I have the following script that should exist if the user does not exist.

#check if user currently exists on system

if id $User > /dev/null 2>&1

then

    #user exists no need to exit program

    echo "blah blah, what a waste of space"

else

    echo "This user does NOT exists.  Please create that user before using this script.

"

    exit

fi

My problem is that I would ideally like to place a "not" if that first if statement so that I can trim down my if, else statement. Ideally I would like something like this:

if !(id $User > /dev/null 2>&1)

then

    echo "This user does NOT exists.  Please create that user before using this script.

"

    exit

fi

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ainsbeave

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answered 2 Years ago admin · Accepted Answer

“Not” is spelled !, with no punctuation and a space after it.

if ! id "$user_name" > /dev/null 2>&1

then

    echo 1>&2 "This user does NOT exists.  Please create that user before using this script.

"

    exit 1

fi

Your proposal would actually work, but the parentheses create a subshell to run the one command id, which is superfluous.

Other changes:

Always put double quotes around variable substitutions: "$user_name"

There is already a variable USER, which is the name of the current logged-in user. Variable names are case-sensitive, but humans not so much.

Return a value between 1 and 125 to indicate failure in a program.

Report errors to standard error (file descriptor 2), not standard output.