You said:

the user define what punctuation they want removed

Presumably, you would have a "default" set (e.g. whatever Perl defines as matching "\W", and maybe "_" as well), which would be suitable in most cases. Actually, a better default might be \P{L} which refers to "all non-letters" (see 'perldoc perlunicode').

If it's important for your application to allow the user to specify a "cusomized" set for some particular case, you face a variety of tricky issues:

• Is it easier for the user to specify the particular non-alphanumerics that should be kept, rather than specify all the ones that should be removed? (I think maybe so.)
• Many of the characters involved have special meanings in regexes (period, question-mark, plus, dollar-sign and some others). This isn't a killer, but you need to be mindful of it.
• If some "non-letter" characters are to be kept when they occur at a word boundary, you might have problems when other "non-letters" (that are to be discarded) co-occur with the ones being kept.

  For example, suppose that hyphen is to be kept at word boundaries, but parens at word boundaries should be removed; in a string like " word)- " it will be hard to remove the paren, because it lies "inside" the hyphen, which is being retained; that paren is "word-internal". Maybe the user just needs to specify which non-letter characters to keep when they occur next to a letter (or maybe it's more complicated than that).

Anyway, in the default case, it really can be very simple (and this might even be the quickest):

use strict;

# make up some data
my $line = "('The text.')-- 5 o'clock! What's cookin' with the text da
+ta?";

# split on whitespace, keep only tokens that contain at least on lette
+r
my @words = grep /\p{L}/i, split ' ', $line;

my %wcount;
for ( @words ) {  # using $_ will modify @words "in-place"
    s/^\P{L}+//;  # remove initial non-letters
    s/\P{L}+$//;  # remove final non-letters
    $wcount{lc()}++;  # normalize to lower-case-only
}

print "$wcount{$_}\t$_\n" for ( sort keys %wcount );

__OUTPUT__
1       cookin
1       data
1       o'clock
2       text
2       the
1       what's
1       with
[download]

Note that even though I was using a regex symbol (\P{L}) that is documented as a "unicode" tool for regexes, I can use it on plain old ASCII data. (If you have non-ASCII data, make sure it's in utf8 before processing it -- see Encode if you have non-utf8, non-ASCII text data.)

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