G'day cavac,

"Sometimes, yes."

Was it just in the range of Perl versions that I indicated? Did it consistently happen in those ranges?

"... at least one person thought this could be a problem big enough to write some code to warn you."

I'm trying to determine why it was a "big enough" problem; and why it was only such a problem across three Perl versions.

"... if you are using vim ..."

Thanks for the tip; however, this problem occurs in legacy $work code (probably over a decade old). I do use vim but I didn't write this code, nor am I its maintainer.

I don't have any systems anymore with such old Perl versions, so i'm limited to my rusty old memory and what i can glean from documentation.

I've read through the relevant perldeltas for 5.20 and 5.26. Both had changes regarding handling of literal control characters in variable names.

5.20 added deprecation warnings and 5.26 made code changes to disallow their use.

After seeing this, my best guess (without knowing the perl internals or grepping through the changelogs) is that the small change for 5.20 has introduced some false positives in control characters detection and 5.26 changed the parser enough that those went away.

My second guess would be a change in the Unicode handler, probably in the way Perl or a script detects Unicode/fileending stuff. v5.20 was the upgrade to Unicode 6.3, v5.26 to 9.0.

I could be totally mistaken, though.

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++ Thankyou very much for your input and the extra checking you performed.

"I could be totally mistaken, though."

You've stated the guesses you've made: they all seem reasonable to me. In the absence of any contradicting information, I'm happy to go along with your explanation.

— Ken