my @ignore=(' ','-'); #whatever
for(@ignore){ s/$_//g; }
#match against $_
[download]

Since in this type of situation I'd normally expect the one pattern to be matched against many strings, I'd usually aim to approach this instead by modifying the regexp:

  my @ignore=(' ','-'); #whatever
  my $ignoreclass = sprintf '[%s]', join '', map quotemeta, @ignore;
  $re = join $ignoreclass, split //, $re;
[download]

Of course this is only so simple if the initial pattern is a simple string: a full-on regexp is rather more difficult to introduce such modifications to reliably.

Hugo

If your ignore set are too complicated for character classes, you can OR them together into a regex. I doubt it would be necessary here, more likely for sets fo words.

my $ignoreStrings =  join "|", @ignore;
my $deleteThese = qr/$ignoreStrings/g;
$strting =~ s/$deleteThese//;
[download]

By the way, you're using $_ to represent the various elements of @ignore, but also to denote the default object of s///. That's why I tend to avoid defaults .... better to be explicit, self-documenting, and avoid irritating errors.

--
TTTATCGGTCGTTATATAGATGTTTGCA

Depending upon how loose you want the criteria to be, you might get away with something like this.

my $term = 'P100';

## my $re = qr[@{[ join '\W*', split '', $term ]}]; # Improved slightl
+y.

my $re = qr[@{[ join '\W*', map "\Q$_\E", split '', $term ]}]x;

for( 
    'P100', 'P-100', 'P 100', 'P1 00', 
    'the P 100 is very similar in style to the P-101 & P102.'.
    'The P-100 is a generation behind the P1000' 
) {
        print "Matched $1" while  m[\b($re)\b]g;
};;
Matched P100
Matched P-100
Matched P 100
Matched P1 00
Matched P 100
Matched P-100
[download]

You could also add /i if you want case insensitivity.

What exactly are you doing in the regexes at the top? What's the difference between the first and second one?