Given the format of your data, you would be much better of using "paragraph mode". Ie. Setting $/ to '' rather than undef. The each read will give you exactly what (I think) you are trying to acheive with your regex.

Try this on your data to see what I mean, the see perlvar $INPUT_RECORD_SEPERATOR for the details.

#! perl -slw
use strict;

local $/ = '';
while( <DATA> ) {
    print "'$_'";
}
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I was trying to avoid using a blank line as a record separator because this file is prone to some corruption and I wouldn't want spurious blank lines interfering with the correct splitting of records.

To use this approach I would have to preprocess the file to strip any blank lines not correctly terminating records.

If I am going to do this I may as well just look for the record itself. How do I only match a string which is followed by a blank line?

You might get away with this, provided the spurious blank lines don't turn up just after the ZONE 001 in the third section of your example dataset.

#! perl -slw
use strict;

my $data = do{ local $/; <DATA> };

print "'$1'" while $data =~ m[
    (
        ^(?:DES|TN)
        .+?
        (?:^DATE|ZONE)
        .+\n\s*(?:\n|$)
    )
]gsx;
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---

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