Recommendation - It is safer to do the initial split like this:

if ($sfreq =~ /^(\d)[.](\d)[.](\d)$/) {
  my $MHz = $1;
  my $KHz = $2;
  my $hz  = $3;

  # rest of code
}
else {
  die "Sorry, invalid input. Please use format '<MHz>.<KHz>.<Hz>'.\n"
}
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