$a=1;
$b=2;

....
    while ($line = <INFILE>)    {
        chomp($line);   # contains $a, $b
        print "$line\n"; #prints "$a" "$b"
[download]

It's not clear what you are trying to achieve. See I know what I mean. Why don't you?

If you read text to print it later, you print text. If you want to replace text (eg. "$a" with "1"), do so with s/\$a/1/ - see perlre.

If you want perl to evaluate the file, say so with eval, do or require. Evaluating a file whilst reading it linewise is tricky and outright impossible if those lines aren't self-contained perl statements (e.g. if the file contains control structures spanning several lines).

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}