Perl Term::ReadKey with Arrow Keys

Question

I'm using Term::ReadKey in ReadMode('cbreak') to read a single character and perform an action based on the input. This works fine for all other keys except the arrow keys. When the arrow keys are pressed, the action is performed 3 times and I understand this is because the arrow keys translate to '^[[A', etc...

How do I translate the arrow keys into some arbitrary single value that the ReadKey can interpret?

I tried the following code but it doesn't work:

use Term::ReadKey;

ReadMode('cbreak');

my $keystroke = '';

while ($keystroke ne 'h') {

    print "Enter key: "; 

    #Read user keystroke 
    $keystroke = ReadKey(0);

    chomp($keystroke);


    if(ord($keystroke) == 27) {
         $keystroke = ('0');
    }
}

Here's my code based on the suggestion:

use Term::RawInput;
use strict;
use warnings;

my $keystroke = '';
my $special = ''; 

while(lc($keystroke) ne 'i' && lc($keystroke) ne 't'){

    my $promptp = "Enter key: ";

    ($keystroke,$special) = rawInput($promptp, 1);

    if ($keystroke ne '') {
        print "You hit the normal '$keystroke' key\n";
    } else {
        print "You hit the special '$special' key\n";
    }

    chomp($keystroke);

    $keystroke = lc($keystroke);
}

if($keystroke eq 'i') {
    #Do something
}

if($keystroke eq 't') {
    #Do something
}

Now, no matter what I press, I can't exit this loop

Here's the output:

Enter key: 
Enter key:
Enter key: You hit the normal 't' key

#Proceeds to function

Answer 1

Here's my working solution...

use Term::ReadKey;

ReadMode('cbreak');

{
    #Temporarily turn off warnings so no messages appear for uninitialized $keystroke
    #that for some reason appears for the if statement
    no warnings;

    my $keystroke = '';

    while ($keystroke ne 'h') {

        print "\nEnter key: ";

        #Read user keystroke 
        $keystroke = ReadKey(0);

        #The first character for the arrow keys (ex. '^[[A') evaluates to 27 so I check for 
        #that
        if(ord($keystroke) == 27) {
            #Flush the rest of the characters from input buffer
            #This produces an 'Use of uninitialized value...' error
            #for the other two characters, hence 'no warnings' at the beginning.
            #This will ignore the other 2 characters and only cause a single iteration
            while( defined ReadKey(-1) ) {}
        }
    ReadMode 0;
    }
}

Answer 2

Term::RawInput doesn't cover everything, but it's a pretty good start for this task:

use Term::RawInput;
my ($keystroke,$special) = rawInput("", 1);
if ($keystroke ne '') {
    print "You hit the normal '$keystroke' key\n";
} else {
    print "You hit the special '$special' key\n";
}

Answer 3

If you're wanting to read high-level semantic ideas of "keypresses", rather than lower-level ideas of "bytes from the terminal" you'll need something that can parse and collect up those multi-byte sequences for you.

For this sort of task, I wrote Term::TermKey:

use Term::TermKey;

my $tk = Term::TermKey->new( \*STDIN );

print "Press any key\n";

$tk->waitkey( my $key );

print "You pressed: " . $tk->format_key( $key, 0 );

Answer 4

Based on mob answer, using Term::RawInput, I did this script to emulate a more complex input interaction. The most important difference is the use of 'rawInput': mob suggested: rawInput("",1), I find out that actually using rawInput("> ") (without the second parameter) makes things easier to work with, and having a prompt ">" is more useful.

This code accepts commands and special keys. Also, it displays nicely to be used as an interactive shell for your system.

DELETE key will remove all chars and BACKSPACE a single character. ESC will exit the shell. You can add more keys to include arrows or anything else to perform special functions. This code will print-out any special key pressed which is not included inside the if..elsif (so you know what you need to add).

use warnings;
use strict;
use Term::RawInput;

sub out {
    my $out = shift;
    print "[ $out ]\n";
}

do {
    my ($keystroke,$special) = rawInput("> ");
    if($special eq 'ESC') {
        print "\n";
        exit;
    } elsif($special eq 'ENTER') {
        out($keystroke);
    } elsif($special ne 'DELETE') {
        if ($keystroke ne '') {
            out($keystroke);
        } else {
            print "'$special' key is not associated\n";
        }
    }
} while(1);

You can implement your commands inside "out";