print "Insert your command:";

$input = <STDIN>;

if ($input eq "help") {
  # do something
}
elsif ($input eq "other command") {
  # do something else
}
##</code><code>##

print "Insert your command:";

$input = <STDIN>;

if ($input =~ /^help\s+(.*)/) {
  # do something
}
elsif ($input =~ /^other command\s+(.*)/) {
  # do something else
}
##</code><code>##

else {
  print "'$input' is not a valid command. Type help for a full list of commands.\n";
}