Create a hash of your expected variable names and value regexes. Then loop through your hash looking for matches:

use strict;
use warnings;

my %expects = (
    PROMPT => 5,
    FOO    => 6
);

for my $evar (keys %expects) {
    if (exists $ENV{$evar}) {
        warn "No match for $evar\n" unless ($ENV{$evar} =~ /\Q$expects
+{$evar}\E/);
    }
    else {
        warn "No $evar in ENV\n";
    }
}
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On a side note, please update your post to add code tags around your code. Read Writeup Formatting Tips.