Mastery of the basic command loop is important. This works the same in Java, C, C++, etc.

The basic structure is some sort of a loop that stops when some "quit" or "exit" condition is satisfied. I like to use "while" loops.

Standard reaction when a blank line is input is to just re-prompt - that is not an error.

Standard reaction when blanks occur either before or after the input, is nothing! These extra leading or trailing blanks are not errors.

#!/usr/bin/perl -w
use strict;

while ( (print "Enter a number: "), 
        (my $number = <STDIN>) !~ /^\s*q(uit)?\s*$/i  
      )
{
     next if $number =~ /^\s*$/;  # re-prompt on blank line
     
     if ($number =~ /^\s*[-+]?[0-9]*\.?[0-9]+\s*$/) #a decimal floatin
+g point
     {
        print "Great! number is: $number\n";
     }
     else
     {
        print "illegal number - try again!\n";
     }
}
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