On Mon, Jul 22, 2024 at 8:05 PM Junio C Hamano <gitster@xxxxxxxxx> wrote: > Over the years, we accumulated the community wisdom to avoid the > common "one-short export" construct for shell functions, but seem to > have lost on which exact platform it is known to fail. Now during > an investigation on a breakage for a recent topic, we found one > example of failing shell. Let's document that. > [...] > Signed-off-by: Junio C Hamano <gitster@xxxxxxxxx> > --- > diff --git a/Documentation/CodingGuidelines b/Documentation/CodingGuidelines > @@ -204,6 +204,33 @@ For shell scripts specifically (not exhaustive): > + - The common construct > + > + VAR=VAL command args > + > + to temporarily set and export environment variable VAR only while > + "command args" is running is handy, but this triggers an > + unspecified behaviour accoreding to POSIX when used for a command s/accoreding/according/ > + that is not an external command (like shell functions). Indeed, > + some versions of dash (like 0.5.10.2-6 found on Ubuntu 20.04) and > + AT&T ksh do make a temporary assignment without exporting the > + variable, in such a case. Do not use it for shell functions. A > + common workaround is to do an explicit export in a subshell, like > + so: > + > + (incorrect) > + VAR=VAL func args > + > + (correct) > + ( > + VAR=VAL && > + export VAR && > + func args > + ) > + > + but be careful that the effect "func" makes to the variables in the > + current shell will be lost across the subshell boundary.
