awk question...

[Claude.P.Cantin at NRC.CA]

I'm writting a script in which a variable takes the value of a userid.
I then want to find out who this userid refers to.

I want to do that in one line, involving awk (I know how to do it using
multiple lines of code).

If the userid is 123, the following would do just fine:

   awk -F: '$3 == 123 {print $1}' /etc/passwd

BUT 123 is the content of a variable, say UID.  The following does NOT
work:

   awk -F: '$3 == $UID {print $1}' /etc/passwd

(the output is NOTHING).

I have tried several variations, including "$UID", and "$3"=="$UID", etc.,
but none worked...

Anyone has an insight????

Thank you,

       Claude Cantin (CANTIN at VM.NRC.CA)