CODEWITHSUNDEEP
linuxshellgrep
Netherar
Netherar

Reputation: 15

How to tell if a user is logged in?

I would like to tell if a user is logged in or not.

if [ "$(who | grep -wq "$1")" == 0 ]
echo $1 "is logged in"

"$(who | grep -w "$1")" is equal to 0 if grep finds $1 (a username) in the list(who). So if the user is in the list, he or she is logged in. What is wrong with this?

Upvotes: 0

Views: 59

Answers (2)

gzh
gzh

Reputation: 3596

In bash, $? is used to save the exit code. you can use it to check the exit code of grep.

who | grep -wq "$1"
if [ $? -eq 0 ]; then
    echo "$1 is logged in"
fi

Upvotes: 0

John Kugelman
John Kugelman

Reputation: 361729

grep doesn't print 0, which is what your script checks for. Its exit code is 0. To check the exit code it's simply:

if who | grep -wq "$1"; then
    echo "$1 is logged in"
fi

Upvotes: 3

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