Hi,
doc{3,4} matches doccc and docccc. Another thing is, that you should move the \. outside the parentheses.
Update: I somehow missed the square brackets. It's just like Grandfather said(Re: perl regular expression). Next time i'll try to focus a bit more while looking at the regex ...
Well, at least the example i gave was correct :).

I'll give you an example programm:

use strict;
use warnings;
my $dirname = "/home/hfob";
opendir my $DH , $dirname or die "failed to open $dirname ($!)\n";
my @files = grep { /\.(html?|txt|pdf|ppt|csv|doc)$/i} readdir $DH;
print "$_\n" for @files;
closedir $DH;
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If you also want to match files which have a format .txt.<some_other_extension>, you could adapt the grep like follows:

my @files = grep { /\.(html?|txt|pdf|ppt|csv|doc)(\.|$)/i} readdir $DH
+;
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Then it will accept end of string (in your case the filename), or a dot after the extension. An example for such a case could be myfile.txt.gz