You just open each file handle in turn and keep pushing the lines on to the array:

my @lines;
open(IN1, '<', 'file1') or die $!;
while(my $line = <IN1>) { 
    chomp $line;
    push @lines, $line;
}
close(IN2);

open(IN2, '<', 'file2') or die $!;
while(my $line = <IN2>) { 
    chomp $line;
    push @lines, $line;
}
close(IN2);


my $size = scalar(@lines);   # Get the size of the array
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I wanted to explore how Perl's closures can be manipulated, and ended up creating an object system by accident.
-- Schemer

Note: All code is untested, unless otherwise stated