Let's see if I can do something while I read your specification.

# "What I essentially need is a way to say..."

my $start_tag     = 'BEGIN';
my $end_constant  = 'END';
my $headerformat  = join('; ', "%s=%s" x 17)."\n"; # XXX ? format for 
+printf() ?
my $headerfile    = 'header000';
my $detailsection = 'detail000';

open IN, '<', $file) or die "Can't read '$file': $!\n";

RECORD: while(defined($_ = <IN>)) {
    my %out;               # we'll capture the "record content" for pr
+intf() here
    if (/$start_tag/) {    # "...start at this character..."
        $. = 0;            # reset line counter
        while(<IN>) {      # "...read each line for the next 17..."
                                       # XXX the specs aren't clear he
+r.
            my ($key, $value) = split; # so I'll just split
            $out{$key} = $value;       # "...assign to values to do
                                       # a printf statement..."
            if($. == 17) { # done with reading the record. do "the pri
+ntf()"
                open HEADER, '>', $headerfile
                    or die "Can't write to '$headerfile': $!\n";
                printf HEADER $headerformat, map { $_,$out{$_} } keys 
+%out;
                close HEADER;
                $headerfile++;     # string increment: header000 -> he
+ader001
                $. = 0;
                open DETAIL, '>', $detailsection
                    or die "Can't write to '$detailsection': $!\n";
                                   # "starting at the 18th line of tha
+t record..."
                while(<IN>) {      # "...read until the end constant..
+."
                    print DETAIL;  # "...and print that straight to 
                                   # a different file..."
                    last if /$end_constant/;
                }
                close DETAIL;
                $detailsection++;
                next RECORD;         # "...and then start the entire l
+oop again."
            }
        }
    }
}
[download]

Poo. That might work, but it's butt ugly and hard to read. Let's refactor that a bit.

open my $fh, '<', $file) or die "Can't read '$file': $!\n";

while(<$fh>) {
    write_record($fh,$headerfile) if /$start_tag/;
    $headerfile++;
}

sub write_record {
    my ($fh, $outfile) = @_;
    my %out;
    $. = 0;
    while(<$fh>) {
        my ($key, $value) = split;
        $out{$key} = $value;

        if ($. == 17) {
            open my $header, '>', $outfile
                or die "Can't write '$outfile': $!\n";
            printf $header $headerformat, map { $_,$out{$_} } keys %ou
+t;
            close $header;

            write_detail($fh,$detailsection);

            $detailsection++;
            return;
        } 
    }
}

sub write_detail {
    my ($fh, $detailfile) = @_;
    open my $detail, '>', $detailfile
        or die "Can't write to '$detailfile': $!\n";
    while(<$fh>) {
        last if /$end_constant/;
        print $detail;
    } 
    close $detail;
}
[download]

Does that make sense to you? If it doesn't, write better specifications ;-)

--shmem

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