Re^3: My first perl script is working, what did I do wrong?

[rjt]

1. You are correct, use strict is not required here. Sorry, old habits die hard. :-)
2. Not quite. Your example will not compile, but a similarly expanded translation of what I wrote would look like:

        for my $field (@fields) {
            $re .= qr/(?<$field>$field\s*)/;
        }

Read $_ for a description of the $_ special variable, but the short version is, if you do not supply a variable name to for, Perl will automatically assume $_.

The regex itself might benefit from a bit more explanation. It's capturing all of the column names including trailing whitespace, and saving those as named captures in %+ for use in the line that builds $tmpl:

    my $tmpl = join(' ', map { "A[".length($+{$_})."]" } @fields);

That generates an (un)pack template string based on the field lengths read from the header, determining the length of each field in @fields by taking the length of the same-named capture in %+ . I'm using map here to "map" the values in @fields to the list that I want: a list of the lengths of each field.