Shell Programming and Scripting

As extracting of the file /etc/passwd the ID´s that have not been used in a range specifies.

Please make your questions more clear..

This would take more time than I have, but as a quick solution I can give you all the current ID's:

awk '{FS=":" ; print $3}' /etc/passwd | sort -n

Or you can find the next available ID above a certain number:

#!/bin/sh
i=$1
awk '{FS=":" ; print $3}' /etc/passwd | sort -n > /tmp/tmpfile
while `grep '^'$i'$' /tmp/tmpfile > /dev/null` ; do
i=`expr $i + 1`
done
echo $i is not in passwd

-mschwage