I love problems like this. My solution might not be the most efficient one, but this would be my first attempt:

#!/usr/bin/perl -w

use strict;
use warnings;

my ($Pattern, $c1, $c2) = '';
while( <DATA> )
{
  /./ or next;
  chomp;
  for (my $i = 0; $i < length($_); $i++)
  {
    ($c1 = vec($_, $i, 8)) > 32 or next;
    $c2 = vec($Pattern, $i, 8);
    $c2 = ($c2 < 33) ? $c1 : $c2;
    vec($Pattern, $i, 8) = ($c1 == $c2) ? $c1 : 42;
  }
  print "\n  INPUT = |$_|\nPattern = |$Pattern|\n";
}
print "\n\nFINAL RESULT:\n\n           $Pattern\n";

__DATA__

 /b/c/
a/b/cdx0/m2/b4/r_a_c1_4/w
a/b/c/p0/m0/b0/r_a_c1_0/q
a/b/c/p0/m0/b0/r_a_c1_1/q
a/b/c/p0/m0/b0/r_a_c1_2/q

a/b/c/p0/m0/b1/r_a_c1_0/q
a/b/c/p0/m0/b1/r_a_c1_1/q
a/b/c/p0/m0/b1/r_a_c1_2/q

a/b/c/p0/m0/b1/r_a_c1_0/q/g/w/t
                             /q

w/b/c/p0/m3/b2/r_a_c
    d/e0/m2/b
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