In that case, hardcode the path:

/usr/bin/id -u

Or always use the GNU version:

/usr/local/bin/id -u # if id is the GNU version installed in /usr/local/bin.

You can get it from coreutils.

Alternatively, you can get it from ps:

Code:

$ ps u $$ |awk 'NR == 2 { print $1 }'
10362

It could be you get a name, in which case you then get it from getent:

Code:

getent `ps u $$ |awk 'NR == 2 { print $1 }'` passwd