You could try something like this:

#!/usr/bin/perl

use Term::ReadKey;

my %seqs = (
            "\e[A"  => "Up",
            "\e[B"  => "Down",
            "\e[C"  => "Right",
            "\e[D"  => "Left",
            "\e[5~" => "PgUp",
            "\e[6~" => "PgDn",
            # ...
           );

ReadMode 4;  # raw mode

my $buf = '';

while (my $key = ReadKey()) {
    
    last if $key eq 'q';      # hit 'q' to quit loop

    $buf .= $key;
    $buf = substr($buf, -4);  # keep last 4 bytes
    
    my $escseq = substr($buf,rindex($buf,"\e"));

    if (exists $seqs{$escseq}) {
        print "$seqs{$escseq}\n";
    }
}
ReadMode 0;  # reset tty
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(There are a few subtle issues with this approach, but it should give you an idea how to approach the problem...)

update: you could also use a dispatch table to execute subs when a certain key is pressed:

#!/usr/bin/perl

use Term::ReadKey;

my $n;

my %seqs = (
            "\e[A"  => sub { $n++;      },   # Up
            "\e[B"  => sub { $n--;      },   # Down
            "\e[C"  => sub { $n += 10;  },   # Right
            "\e[D"  => sub { $n -= 10;  },   # Left
            "\e[5~" => sub { $n += 100; },   # PgUp
            "\e[6~" => sub { $n -= 100; },   # PgDn
           );

ReadMode 4;  # raw mode

my $buf = '';

while (my $key = ReadKey()) {
    
    last if $key eq 'q';      # hit 'q' to quit loop

    $buf .= $key;
    $buf = substr($buf, -4);  # keep last 4 bytes
    
    my $escseq = substr($buf,rindex($buf,"\e"));

    if (exists $seqs{$escseq}) {
        $seqs{$escseq}->();   # call associated subroutine
        print "$n\n";
    }
}
ReadMode 0;  # reset tty
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2 ideas:

a) the bad one: continue translating the rest into perl and worry later by temporarily using $key=`read -n3 key; echo \$key`;. Advantage: you stick to the task at hand.

b) the trivial one would be something like $c=""; do{$c.=ReadKey(0); last if $c=~/[\x0a]/} for (1..<small number for sequence length max>);. (0x0a/LF would also resynchronize the user's notion of 'char sequence starts' with the terminal's notion - 'the may need to press enter' bit).

both quick&dirty approaches should be only used for a very small number of expected keys. At least the user can resynch the tty by pressing enter, so it's not too bad.

Maybe there's a simple module in between ReadKey and full Curses to get the whole key sequence into a variable. Anyone has seen possible candidates?

Might be quest-level stuff for the general case:)

update:

please also include non-curses / partial terminal handling modules, if they offer abstractions beyond ReadKey.

Thx to bichonfrise for his pointer Curses::Simple.

My own hoard of never-used just-in-case-examples lists perlmenu, Curses/Perl::UI, and Curses::Widgets, all of which are rather complete user interfaces on a level far higher than ReadKey. Lower than ReadKey and of historic interest is the approach in Larry Wall's process-killer zap of camelbook fame. Might have appeared already in the 1st Ed as it was pure perl4 and eminently hackable.

When I try this,

#!/usr/bin/perl

$key=`read -n3 key; echo \$key`;
print "$key\n";
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I get this error...

read: 1: Illegal option -n
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Don't expect portability from shell builtins across multiple versions or multiple shells. Try w/o the -n3, but then you always need to press CR.

When I try this,

#!/usr/bin/perl

use Term::ReadKey;
use strict;

my $c=""; do{$c.=ReadKey(0); last if $c=~/[\x0a]/} for 1..3;
print "$c\n";
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I still have to press ENTER key for the input to stop after the 3 characters. For example,

$# 12345 <ENTER KEY>
123
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Hm. Try Almut's post's below: it shows an use of the ReadMode 4 setting. For more info, read perldoc -m Term::ReadKey.