Re^2: Split and print hash based on regex

[Maire]

This is a very good question, thanks! And I'm guessing from your response that this may lie at the heart of the problem? The original script that I am working with (reproduced now in an edit to my original post) used very similar syntax successfully, but I need to think about how the original script manages to populate $_ and my modified script doesn't.

[choroba]

while (<DATA>)

is equivalent to

while ($_ = <DATA>)

which is interpreted as

while (defined($_ = <DATA>))

So that's how $_ is populated in the original script.

There's another question, though: How $1 is populated. Note that the matching uses =, not =~, so it's equivalent to

my($regex) = ($_ =~ /This is/g)

where the parentheses after my enforce the list context on the match, but without a capture group in the regex, there's no way to populate $1.

[Maire]

Ah okay, that makes a lot more sense now. Thank you for your very clear explanation: it's very much appreciated.

[AnomalousMonk]

choroba is not wrong to write here that "... without a capture group in the regex, there's no way to populate $1." But as always with regexes, it's more complicated:

c:\@Work\Perl\monks>perl -wMstrict -le
"$_ = 'This is not an exit';
 ;;
 if (my ($regex) = /This is/g) {
   print qq{matched, captured '$regex'};
   }
"
matched, captured 'This is'

Due to the influence of the  /g modifier, something is captured, it's just not anything useful | useful in this case. The only purpose the capture serves in the second OPed SSCCE (the one added in an update) would be to produce a perplexing error message if the open operation failed in the
    open ... or die "could not open 'UserA$regex.txt' $!";
statement. See Matching in list context in perlop.