This works,('min23' in haystack is replaced by 'new') but it seems messy. 
use strict;
use warnings;

my $needle = 'mo4\dy13\hr19\\'; #escape final backslash
$needle =~ s/\\/\\\\/g; # escape all backslashes or they will mess up 
+the regex
my $haystack = '\yr2012\mo4\dy13\hr19\min23\sec51';
if ($haystack =~ /$needle(.*?3)/) {
  print "found $1\n";
  my $match = $1;
  my $replacement = 'new';
  my $newneedle = $needle;
  $newneedle =~ s/\\\\/\\/g; # unescape the backslashes or there will 
+be too many in the final string
  $haystack =~ s/$needle$match/$newneedle$replacement/; # I want all v
+ariables here, not literal strings
} else {
  print "not found\n";
}
print "$haystack\n";

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In reply to Is there a nicer way to do regex search and replace with literal backslashes? by Anonymous Monk

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