For instance:

print "Insert your command:";

$input = <STDIN>;

if ($input eq "help") {
  # do something
}
elsif ($input eq "other command") {
  # do something else
}
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Of course, if your commands are allowed to receive parameters,

print "Insert your command:";

$input = <STDIN>;

if ($input =~ /^help\s+(.*)/) {
  # do something
}
elsif ($input =~ /^other command\s+(.*)/) {
  # do something else
}
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The parameters (the full string following the original command and any spaces after it) will be store in the special variable $1

You can even have a final condition for the case in which the inserted command was not valid:

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