You can use quotemeta or \Q \E regex escapes to be sure, like this:

my $match = quotemeta('tftp>');
if ($str =~ /$match/) { 
 ...
}
[download]

or

my $match = 'tftp>';
if ($str =~ /\Q$match\E/) {
  ...
}
[download]

or using the value directly

if ($str =~ /\Qtftp>\E/) {
   ...
}
[download]