fu (free uid)

fu - find free user id
Usage:  fu [OPTIONS] [START]
Options:
  -2   Limit range to START+99
  -3   Limit range to START+999
  -4   Limit range to START+9999
  -5   Limit range to START+99999
  -6   Limit range to START+999999
  -n   Don't add 1 to the START value after calculating the range.
  -v   Verbose output
  -h   This help
  -V   Program version

If no START value is given, the default is 1000. If no range is given
(options -23456), fu calculates the range by examining the START value:
Every trailing zero of that value will be variable.
(E.g. for a start value of 31000, the range will be 31000..31999,
therefore if no range and no start value are given, the default range
will be 1000..1999.)
Usually fu adds 1 to the start value (after calculating the range)
so the start value itself won't ever be used as an user id.
You may prevent this with the -n option.
If no free id was found in the allowed range, fu prints -1
(or an error if in verbose mode) and exits with exit status 1.