What have you tried? What version of Perl are you using? How are you defining the value of a "variable" within a text file (eg, is it a particular configuration file format)?

Here's something that may or may not match your description and requirements (mostly untested code):

use strict;
use warnings;
use 5.10; # ~~ operator requires Perl version >= 5.10
use Util::Any -all;
use Perl6::Slurp;
use File::chdir;
use Cwd "abs_path";

say for
map   { map { (split)[1] } grep { /baz/ } @$_ } # value of "baz"
grep  { "foo bar" ~~ $_ } # "foo" has the value "bar"
map   { [slurp] }
grep  { looks_like_number $_ }
map   { $CWD = $_ and <*> }
apply { abs_path $_ } # dies on error
$ARGV[0]
[download]