#!usr/bin/perl-w
use strict;
use Term::ReadKey;

my @cmd = (0..200);
$|=1;
my $i=0;
while (1){
    print join "\n",grep {!/^$/} @cmd[$i*20 .. ((++$i*20)-1)],'';
    last if (20*$i > $#cmd);
    warn "\nPlease press a key to continue.\n";
    my $key;
        while (not defined ($key = ReadKey(-1))) {  }
}
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perl theprogram | less
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Trying to reinvent that particular wheel in Perl is not a thing I care about much.

use warnings;
use strict;

my @cmd = 1 .. 200;
my $i = 0;
for (@cmd) {
    print "$_\n";
    $i++;
    sleep 2 if $i % 20 == 0;
}
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See also:

• perlintro
• perlop

#!/usr/bin/perl
use warnings;
use strict;
use Term::ReadKey;

my $char='q';
my @array = ('aa' .. 'zz');
my $print_go = 1;
my $ch;

while(1){

ReadMode ('cbreak');

if (defined ( $ch = ReadKey(-1))){ 
    #input was waiting and it was $ch
     print "$ch\n"; 
     if ($ch eq $char){exit(0)};
     if ($ch eq ' '){ $print_go = 0 }; #space stops print
     if ($ch eq 'g'){ $print_go = 1 };
     if ($ch eq 'x'){ exit };
   print "$ch\n";
   
 }else{
    # no input was waiting
    #your program goes here
 #   print "############################\n";
    
    my $val = shift @array;
    
    if( $print_go ) { print "$val\n" }
    
    select(undef,undef,undef,.1);

}

ReadMode ('normal'); # restore normal tty settings
}
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Here's a potential solution using the each() for arrays feature in 5.12:

#!/usr/bin/perl

use warnings;
use strict;
use 5.12.0;

my @array = ( 'aa'..'zz' );

while ( my ( $i, $elem ) = each @array ){
    if ( $i != 0 && $i % 20 == 0 ){
        say "Hit ENTER to continue...";
        <STDIN>;
    }
    say $elem;
}
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If you don't have perl v5.12+, you'll need to use an external iterator:

my $i = 0;
for my $elem ( @array ){
    if ( $i != 0 && $i % 20 == 0 ){
        say "Hit ENTER to continue...";
        <STDIN>;
    }
    say $elem;
    $i++;
}
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