How to substitute arbitrary fixed strings in Perl

Question

I want to replace a fixed string within another string using Perl. Both strings are contained in variables.

If it was impossible for the replaced string to contain any regex meta-characters, I could do something like this:

my $text = 'The quick brown fox jumps over the lazy dog!';
my $search = 'lazy';
my $replace = 'drowsy';

$text =~ s/$search/$replace/;

Alas, I want this to work for arbitrary fixed strings. E.g., this should leave $text unchanged:

my $text = 'The quick brown fox jumps over the lazy dog!';
my $search = 'dog.';
my $replace = 'donkey.';

$text =~ s/$search/$replace/;

Instead, this replaces dog! with donkey., since the dot matches the exclamation mark.

Assuming that the variable contents themselves are not hardcoded, e.g., they can come from a file or from the command line, is there a way to quote or otherwise markdown the contents of a variable so that they are not interpreted as a regular expression in such substitution operations?

Or is there a better way to handle fixed strings? Preferably something that would still allow me to use regex-like features such as anchors or back-references.

Answer 1

Run your $search through quotemeta:

my $text = 'The quick brown fox jumps over the lazy dog!'; 
my $search = quotemeta('dog.'); 
my $replace = 'donkey.'; 

$text =~ s/$search/$replace/;

This will unfortunately not allow you to use other regex features. If you have a select set of features you want to escape out, perhaps you can just run your $search through a first "cleaning" regex or function, something like:

my $search = 'dog.';
$search = clean($search);

sub clean {
  my $str = shift;
  $str =~ s/\./\\\./g;
  return $str;
}

Answer 2

Wrap your search string with \Q...\E, which quotes any meta characters within.

$text =~ s/\Q$search\E/$replace/;