You want to use the CGI.pm module, which can parse that:

use strict;
use CGI;

my $string = "name=alex&sex=m&age=20";
my $q=CGI->new($string);
print Dumper scalar $q->Vars()"
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If you actually are, as it looks, parsing a CGI query, the CGI module can also take all of the other chores of parsing CGI queries for you:

use strict;
use CGI;

my $q=CGI->new(); # parses all CGI parameters

print $q->header('text/plain');
print Dumper scalar $q->Vars()"
[download]