$ perl -E '
> open my $fa, q{<}, \ <<EOF1 or die $!;
> file A line 1
> file A line 2
> EOF1
> 
> open my $fb, q{<}, \ <<EOF2 or die $!;
> file B line 1
> file B line 2
> EOF2
> 
> say join q{,},
>    map { chomp; $_ } scalar <$fa>, scalar <$fb>;'
file A line 1,file B line 1
$