Perl Porter Stemmer - perl

Question

I was checking this porter stemmer. Below they said I should change my first line. To what exactly I tried every thing but the stemmer ain't working. What a good example might be?
#!/usr/local/bin/perl -w
#
# Perl implementation of the porter stemming algorithm
# described in the paper: "An algorithm for suffix stripping, M F Porter"
# http://www.muscat.com/~martin/stem.html
#
# Daniel van Balen (vdaniel#ldc.usb.ve)
#
# October-1999
#
# To Use:
#
# Put the line "use porter;" in your code. This will import the subroutine
# porter into your current name space (by default this is Main:: ). Make
# sure this file, "porter.pm" is in your #INC path (it includes the current
# directory).
# Afterwards use by calling "porter(<word>)" where <word> is the word to strip.
# The stripped word will be the returned value.
#
# REMEMBER TO CHANGE THE FIRST LINE TO POINT TO THE PATH TO YOUR PERL
# BINARY
#
As A code I am writing what follows:
use Lingua::StopWords qw(getStopWords);
use Main::porter;
my $stopwords = getStopWords('en');
#stopwords = grep { $stopwords->{$_} } (keys %$stopwords);
chdir("c:/perl/input");
#files = <*>;
foreach $file (#files)
{
open (input, $file);
while (<input>)
{
open (output,">>c:/perl/normalized/".$file);
chomp;
porter<$_>;
for my $stop (#stopwords)
{
s/\b\Q$stop\E\b//ig;
}
$_ =~s/<[^>]*>//g;
$_ =~ s/[[:punct:]]//g;
print output "$_\n";
}
}
close (input);
close (output);
The code gives no errors except it is not stemming anything!!!

Answer 1

That comment block is full of incorrect advice.
A #! line in a .pm file has no effect. It's a common mistake. The #! line tells Unix which interpreter to run the program with if and only if you run the file as a command line program.
./somefile # uses #! to determine what to run somefile with
/usr/bin/perl somefile # runs somefile with /usr/bin/perl regardless of #!
The #! line does nothing in a module, a .pm file which you use. Perl is already running at that point. The line is nothing but a comment.
The second problem is that your default namespace is main not Main. Casing matters.
Moving on to your code, use Main::porter; should not work. It should be use porter. You should get an error message like Can't locate Main/porter.pm in #INC (#INC contains: ...). If that code runs, perhaps you moved porter.pm into a Main/ directory? Move it out, it will confuse the importing of the porter function.
porter<$_>; says "try to read a line from the filehandle $_ and pass that into porter". $_ isn't a filehandle, it's a line from the file you just opened. You want porter($_) to pass the line into the porter function. If you turn on warnings (add use warnings to the top of your script) Perl will warn you about mistakes like that.
You'll also presumably want to do something with the return value from porter, otherwise it will truly do nothing. my #whatever_porter_returns = porter($_).
Likely one or more of your chdir or opens have silently failed so your program may have no input. Unfortunately, Perl does not let you know when this happens, you have to check. Normally you add an or die $! after the function to check for the error. This is busy work and often one forgets, instead you can use autodie which will automatically produce an error if any system calls like chdir or open fail.
With that stuff fixed your code should work, or at least produce useful error messages.
Finally, there are many stemming modules on CPAN which are likely to be higher quality than the one you've found with documentation and tests and updates and all that. Lingua::Stem and Text::English specifically use the porter algorithm. You might want to give those a shot.