It wouldn't have generated an error*, but you may be Suffering from Buffering?. To find out, change your code to the following:

#!/usr/bin/perl
$|++;
print "Hello World/n";
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--Jim

Update1: Added the "/" to the shebang. Note that executing this program will look something like the following since your newline is mangled:

prompt> helloworld.pl
Hello World/nprompt>
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Update2: * provided you ran your program from the root (/) directory, the relative path would've worked if the rest (usr/bin/perl) was correct.