Actually this will not work if the string includes numbers in the part that you match with \D. I think you have to "unroll the loop" if you want to avoid (.*?):

#!/bin/perl -w
use strict;
foreach( <DATA>)
  { s{^\d+_                          # start then number(s) then _
       ((?:\D*(?:\d(?!\d*_))?)*)     # non_digits then optionnaly
                                     #   a digit _not_ followed by dig
+its and _
                                     # repeat, rince...
       \d+_                          # the second digit _ sequence
       (.*)}                         # the rest of the string
     {$1$2}x;
    print;
  }

__DATA__
1_abc/2_deg/bla_30_31_blah
1_ab1c/2_deg/bla_30_31_blah
1_ab1c/22_deg/bla_30_31_blah
1_a2b33c/22_deg/bla_30_31_blah
a_ab1c/b_deg/bla_30_31_blah
[download]

Note that your regexp will not work properly for the second string. I also added a line where the regexp does not match as this can show bugs when a badly written regexp takes for ever to match on a string that it does not match.

Frankly it this case, and despite all the warnings around, I would use (.*?) and write the regexp as:

I would be happy to get enlightened as to why this is not safe by the way.