Reading Single Character Input with Term::ReadKey

qazwart has asked for the wisdom of the Perl Monks concerning the following question:

UPDATE: Never mind. I figured it out. It was doing exactly what it was support to do.

The real problem was my code in the previous section.

In my application, I ask for the user's input, but if the user presses a "Ctrl-H", I want to display a help screen, and if the user presses a "Ctrl-P", I want to go back to the previous question.

I've found the "Term::ReadKey" module and did a small little test:

#! /usr/bin/env perl

use strict;
use warnings;

use Term::ReadKey;

ReadMode "raw";
my $key = ReadKey(0);
ReadMode "restore";
print "Backspace detected!\n" if ($key eq "^H");

my $foo = <STDIN>;
print "ASCII Code Value = " . ord($key) . "\n";
print "Complete Answer = " . $key . $foo . "\n";
print "You typed a \"$key\"\n";
[download]

Works like a charm! Now, I apply this same technique to my program:

   print "\n\nANSWER";
   if (defined($default)) {
       print " [Default = $default]";
   }
   print ": ";
   ReadMode "raw";
   my $key = ReadKey(0);
   ReadMode "restore";
   if ($key eq "^H") { #Help Mode!
       $showHelpFlag = 1;
       redo;
   }
   chomp($answer = $key . <STDIN>);
[download]

No good! When I print the value of "$key", it shows the correct ASCII value, but it doesn't seem to read control characters, so it simply ignores "Ctrl-H" presses.

So, why does the test program work, but the same code in my more complex program doesn't? BTW, the code is in a part where I redefined the package name. I'm making a feeble attempting to do object oriented programming. Would this do anything?

Comment on Reading Single Character Input with Term::ReadKey Select or Download Code

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Re: Reading Single Character Input with Term::ReadKey by BrowserUk (Patriarch) on Apr 17, 2007 at 18:20 UTC
Try changing `"^H"` for `"\cH"` or `"\x08"`. `"^H"` is just a 2 character string consisting of the characters '^' & 'H'. The other two are escape sequences that perl interprets at compile time and substitutes the approriate single control chracter, `chr(8)`. Indeed, it might be clearer to others and yourself later if you used `if ($key eq chr(8) ) { #Help Mode!` [download] Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply] [d/l] [select]
Re^2: Reading Single Character Input with Term::ReadKey by Fletch (Bishop) on Apr 17, 2007 at 18:25 UTC
Even clearer would be to hide that in a constant rather than having a bare magic number . . . `use constant HELP_KEY => chr( 8 ); ## Control H if( HELP_KEY() eq $key ) { ## . . . }` [download] Alternately: `use Readonly; Readonly my $HELP_KEY => chr( 8 ); ## Control H if( $HELP_KEY eq $key ) { ## . . . }` [download]	[reply] [d/l] [select]
Re^3: Reading Single Character Input with Term::ReadKey by BrowserUk (Patriarch) on Apr 17, 2007 at 18:52 UTC
I agree, but it is different advice. I was making suggestions on how best to define the constant. You are suggesting that he should use a symbolic constant in place of the actual constant. Ie. You could have made your point by suggesting `use constant HELP_KEY => "\cH"; ## Control H` [download] And my point would still hold. As for Readonly; I "Just Say No", but that's apparently controversial :) Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply] [d/l]
Re: Reading Single Character Input with Term::ReadKey by shmem (Chancellor) on Apr 17, 2007 at 18:16 UTC
Maybe you'd do better saying `if ($key eq "\cH") { ... }` [download] and in your sample snippet you're not printing that char. --shmem _($_=" "x(1<<5)."?\n".q·/)Oo. G°\ / /\_¯/(q / ---------------------------- \__(m.====·.(_("always off the crowd"))."· ");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}	[reply] [d/l]