You could also use the $ENV{} hash to access the brower string. The user agent/browser info is stored in $ENV{HTTP_USER_AGENT}. Your code would change to :

my $browser = $ENV{HTTP_USER_AGENT};
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I use this little program to see what is available on the different browsers that I test.

#!/usr/bin/perl
##
##  printenv -- print the environment
##

print "Content-type: text/plain\n\n";
foreach $var (sort(keys(%ENV))) {
    $val = $ENV{$var};
    $val =~ s|\n|\\n|g;
    $val =~ s|"|\\"|g;
    print "${var}=\"${val}\"\n";
}
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