Perl Hacks

Hack #14. Simplify Your Terminal Interactions

Read data from users correctly, effectively, and without thinking about it.

Even when you know the right way to handle interactive I/O [Hack #13], the resulting code can still be frustratingly messy:

my $offset;
print "Enter an offset: " if is_interactive;
GET_OFFSET:
while (<>)
{
    chomp;
    if (m/\\A [+-] \\d+ \\z/x)
    {
        $offset = $_;
        last GET_OFFSET;
    }
    print "Enter an offset (please enter an integer): "
        if is_interactive;
}

You can achieve exactly the same effect (and much more) with the prompt( ) subroutine provided by the IO::Prompt CPAN module. Instead of all the above infrastructure code, just write:

use IO::Prompt;

my $offset = prompt( "Enter an offset: ", -integer );

prompt( ) prints the string you give it, reads a line from standard input, chomps it, and then tests the input value against any constraint you specify (for example, -integer). If the constraint is not satisfied, the prompt repeats, along with a clarification of what was wrong. When the user finally enters an acceptable value, prompt( ) returns it.

Most importantly, prompt( ) is smart enough not to bother writing out any prompts if the application isn't running interactively, so you don't have to code explicitly for that case.

Tip

Infrastructure code is code that doesn't actually contribute to solving your problem, but merely exists to hold your program together. Typically this kind of code implements standard low-level tasks that probably ought to have built-ins dedicated ...