In general, I'd recommend using a module such as one of those already described.

For a quick-and-dirty script, where all options take values like the ones you've described, you can slurp @ARGV into a hash:

#!/usr/bin/env perl -l

use strict;
use warnings;

my %opt = @ARGV;

print qq{Option $_ = }, $opt{$_} for sort keys %opt;

print qq{-z option detected: $opt{-z}} if exists $opt{-z};
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Example runs:

$ pm_in_params.pl -i infile -o outfile -s statfile
Option -i = infile
Option -o = outfile
Option -s = statfile

$ pm_in_params.pl -i infile -o outfile -s statfile -z zzzzzzzz
Option -i = infile
Option -o = outfile
Option -s = statfile
Option -z = zzzzzzzz
-z option detected: zzzzzzzz
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