ABC a b c value=3.14
+ value2="2.04"

##</code><code>##

ABC a b c value=3.14
+ value2="2.04"
+ value3=text

##</code><code>##

while (defined(my $lineA = <FILE_A>) && defined(my $line_b = <FILE_B>)) {
...
compare_line(lineA=$lineA, lineB=$lineB);
...
}