Depends upon what you want in terms of data validation. Your example shows two integer numbers, so that is what this does. Oh, BTW do not use $a or $b as variables in a Perl program as they have special meanings in sort().

I think this would have worked out better if I had only used regex, but my brain was on this "split" subject. But in any event, this shows how to detect too many arguments on the input line, what I just called "kruft".

#!/usr/bin/perl -w
use strict;

my $line;
my ($x,$y);
my $two_nums_valid =0;

while ( (!$two_nums_valid) and (print "enter 2 integer numbers: ") 
                           and ($line =<STDIN>) )     
{
   next if $line =~ /^\s*$/;  # just re-prompt on blank lines
   
   chomp $line;       #needed here to detect real $kruft
   ($x, $y, my $kruft) = split (' ', $line);
   
   if (defined $kruft)
   {
      print "illegal format - only two integer numbers allowed!\n";
      next;
   }
   
   if (!defined $y or $x !~ /^\d+$/ or $y !~ /^\d+$/)
   {
      print "two integer numbers are needed, like: 10 20\n";
      next;
   }
   
   $two_nums_valid =1; 
}

print "hooray the numbers are: $x and $y\n";

__END__
C:\TEMP>perl inputXY.pl
enter 2 integer numbers: a b
two integer numbers are needed, like: 10 20
enter 2 integer numbers: a b 10
illegal format - only two integer numbers allowed!
enter 2 integer numbers: a 10
two integer numbers are needed, like: 10 20
enter 2 integer numbers: 10 a 20
illegal format - only two integer numbers allowed!
enter 2 integer numbers: 2 2.5
two integer numbers are needed, like: 10 20
enter 2 integer numbers: 20
two integer numbers are needed, like: 10 20
enter 2 integer numbers: 20 b
two integer numbers are needed, like: 10 20
enter 2 integer numbers: 30 44
hooray the numbers are: 30 and 44
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