my @required_chars = qw/p e r l/; # Or anything else...
LINE:
while (<>) {
  foreach my $char (@required_chars) {
    next LINE unless index($_, $char) >= 0;
  }
  print;
}

##</code><code>##

#!perl -w
# Warning - silly way of solving problem
use strict;
# CPAN, how we love thee
use Math::Combinatorics;

my @required_chars = qw/p e r l/; # Or anything else...
# For bonus points, we could create a package which blessed
# the regexp into an object. But that would be silly.
my $re = make_re(@required_chars);
while (<>) {
  print if /$re/;
}

sub make_re
{
  # Get all N! ways of arranging the chars
  my @combinations = permute(@_);
  # Construct a.*b.*.*d strings, for each
  my @res = map { join(".*", @$_); } @combinations;
  # Put them together into a honking great regexp
  my $re = "(" . join("|", @res) . ")";
  return qr/$re/;
}