You're treating arbitrary text as a regex pattern, so it doesn't match what you expect it to match and it you get regex pattern compilation errors:

Unmatched ( in regex; marked by <-- HERE in m/mozilla/5.0 ( <-- HERE m
+acintosh; u; safari/525/ at script.pl line 30.
[download]

I'm rather curious as to why you didn't mention that you were getting an error.

Perhaps you want

# Does $user contain the string from $useragent
$user =~ /\Q$useragent\E/
[download]

or

# Is $user equal to the string from $useragent
$user =~ /^\Q$useragent\E\z/
[download]

or

# Is $user equal to the string from $useragent
$user eq $useragent
[download]