Find out if unix user names (multiple) exists using shell script

Question

I have the following script which checks whether the given username "alice" exists in the system.

if id "alice" >/dev/null 2>&1; then
        echo "user exists"
else
        echo "user does not exist"
fi

I want to check whether alice, bob and carol exists. So, when I use AND in the following code, I do get the right results probably, but it prints the unnecessary line from id command.

if id "alice" && id "bob" && id "carol" >/dev/null 2>&1; then
        echo "user exists"
else
        echo "user does not exist"
fi

The output is as follows:

uid=1001(alice) gid=1002(alice) groups=1005(somegroupname),1002(alice)
uid=1002(bob) gid=1003(bob) groups=1005(somegroupname),1003(bob)
user exists

I want to make sure that if alice, bob or carol are not present as users, I want to print a meaningful message stating

<this_speicific_user> is not present.

anubhava · Accepted Answer · 2017-09-22 08:42:43Z

2

You can use braces to group all 3 commands into one group:

{ id "alice" && id "bob" && id "carol"; } >/dev/null 2>&1

answered Sep 22, 2017 at 8:42

anubhava

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3 Comments

kingmakerking Over a year ago

Thanks. But how to print a message, let's say alice is not present?

kingmakerking Over a year ago

I get the error as test.sh: line 16syntax error near unexpected token `if' test.sh: line 16: `if ! id "$u" >/dev/null 2>&1; then '

anubhava Over a year ago

Sorry do is missing. Use: for u in alice bob carol; do if ! id "$u" >/dev/null 2>&1; then echo "$u does not exist"; fi; done

P.P · Accepted Answer · 2017-09-22 08:44:09Z

0

You can redirect the stderr of each command:

if id "alice" >/dev/null 2>&1 && id "bob" >/dev/null 2>&1 && id "carol" >/dev/null 2>&1;
then
        echo "user exists"
else
        echo "user does not exist"
fi

Oor use a compound command:

if { id "alice" && id "bob" && id "carol"; } >/dev/null 2>&1; then
        echo "user exists"
else
        echo "user does not exist"
fi

answered Sep 22, 2017 at 8:44

P.P

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Comments

Gaétan RYCKEBOER · Accepted Answer · 2017-09-22 10:31:27Z

0

Use the || as you did with && :

{ test1 && test2 && test3 } || else_function

If your request is to show all unset users, it is a bit more tricky, but use negative check:

{ ! id "alice" && echo "alice absent." } || { ! id "bob" && echo "bob absent." } || { ! id "walter" && echo "walter absent." }

or even:

absent=false
for user in alice bob walter ; do
   ! id "$user" && echo "$user is absent." && absent=true
done
$absent || echo "All users are present."

edited Sep 22, 2017 at 10:31

answered Sep 22, 2017 at 10:24

Gaétan RYCKEBOER

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Comments

Erik Bennett · Accepted Answer · 2017-09-25 23:35:59Z

0

I think the general answer is that if you want a specific error, you need a specific test. That is, if you test for ( condA || condB || condC ), it's not straightforward to find out which of those conditions failed.

Also, if you want to test them all, no matter what, you'll need to break them out into separate tests. Otherwise if id "alice" fails, the others won't get tested due to short circuiting.

answered Sep 25, 2017 at 23:35

Erik Bennett

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