If you're always looking for prefixes, then something like this may get you the pattern:

sub prefix {
  my $prefix = shift;
  for (@_)
  {
      next if $prefix eq substr($_, 0, length $prefix);
      chop $prefix;
      redo;
  }
  $prefix;
}
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Then you just put a * at the end of whatever it returns. If you want to find the longest shared string, well, that would be a bit more difficult.