I often want to do something like $a =~ s/$b/$c/g , where $b is a variable that may have regex metacharacters in it. Here's an example of the problem: 
my $a = "$";
my $b = "$";
my $c = "x";

$a =~ s/$b/$c/g;

print "a=$a\n";

[download]
This results in an error, because the string $b has a regex metacharacter, $, in it. Here's the alternative I've come up with so far: 
# conceptually, the following is like $a=~s/$b/$c/, but is safe if $b 
+has metacharacters in it
sub string_substitution_one {
  my $a_ref = shift;
  my $b = shift;
  my $c = shift;
  my $a = $$a_ref;
  my $debug = ($b eq '$m$');
  my $i=index($a,$b);
  return 0 if $i == -1;
  my $z = '';
  if ($i>0) {$z = $z . substr($a,0,$i)}
  $z = $z . $c;
  if ($i+length($b)<length($a)) {$z = $z . substr($a,$i+length($b),len
+gth($a)-($i+length($b)))}
  $$a_ref = $z;
  return 1;
}

# conceptually, the following is like $a=~s/$b/$c/g, but is safe if $b
+ has metacharacters in it
sub string_substitution_global {
  my $a_ref = shift;
  my $b = shift;
  my $c = shift;
  my $found = 0;
  while (string_substitution_one($a_ref,$b,$c)) {
    $found = 1;
  }
  return $found;
}

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Is there a simpler way to do this? I'm thinking of making this into a module, because I have several different programs that use it, but it seems like there must be an easier way to do such a common task. TIA!

In reply to s/$foo/$bar/ when $foo has metacharacters in it by bcrowell2

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