I think the example code is bad. The correct code is

#!/usr/bin/perl

$num=20;
while ($num<30) {
   print "num is $num\n";
   $num=$num+1;
}
[download]

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Español

El codigo que esta de ejemplo esta mal este es el correcto

#!/usr/bin/perl

$num=20;
while ($num<30) {
   print "num is $num\n";
   $num=$num+1;
}
[download]

20041020 Edit by ysth: use p, code, hr tags; fix tilde-n