I tried also to run the code on the file. It's run perfectly on my system after throwing away the header.

I still suspect you have somewhere unexpected characters in your input. The errors point to that. This can be invisible characters that aren't visible and can't be automatically transformed by Perl to a number. Try to validate your input by something like this:

unless ($F2[2] =~ /^[+-]?\d+\.?\d*$/) {print "not an floating number\n
+";} #assumes "." as digital separator, no thousand separator
unless ($F3[2] =~ /^[+-]?\d+\.?\d*$/) {print "not an floating number\n
+";}
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Look also to http://www.perlmonks.org/?node_id=622704 for a more in detail explanation. It is possible that later versions of Perl are more robust in transforming a string to a number.

Martell

How bizarre. I've tried running it on 5.25.2 and 5.24.0 installed via Perlbrew. Same error each time.

It seems to be caused by something earlier in the script (this chunk of code forms a subsection of it) - running my file using your wrapped code allows it to run to completion.

Why exactly it fails near the end of a file when it's part of a larger script but not when it's separate is beyond me.

It seems to be caused by something earlier in the script

Does the earlier code read the same file? Does the earlier code use much memory?

Perhaps you should post the entire script.

---

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I've found the cause. I used incorrect syntax to try and close multiple filehandles

close ($OUT,$OUT2,$IN)
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But despite using warnings + strict, I never received a message about this until I switched back to the system Perl. As the input file for this chunk of code is created earlier in the script - not having the filehandle closed led to the error.

I'm still unclear as to how the script was able to run to completion on some, typically smaller input files - but not others given that almost no memory is required until this step.