On Tue, May 31, 2016 at 10:31:59PM -0400, Jeff King wrote:
> On Tue, May 31, 2016 at 08:09:43PM -0400, Eric Sunshine wrote:
>
> > I was under the impression that the project was moving toward 'env' to
> > deal[1] with this sort of issue.
> >
> > [1]: 512477b (tests: use "env" to run commands with temporary env-var
> > settings, 2014-03-18)
>
> We can use it with test_must_fail, because it takes a command name:
>
> test_must_fail env FOO=BAR whatever-you-would-have-run
>
> But I don't think it works in the general case, as test_commit does not
> run its arguments. So you'd want something like:
>
> env FOO=BAR test_commit exotic
>
> but of course that doesn't work because "env" can't find the shell
> function. I think with bash you could do:
>
> export test_commit
> env FOO=BAR bash -c test_commit exotic
>
> but we can't rely on that.
I wondered if we could implement our own "env" in the shell, but it's a
little non-trivial, because:
- our basic tool for setting variable-named variables is "eval", which
means we need an extra layer of quoting
- we have to restore the variables after. That means telling the
difference between unset and empty (possible with "-" versus ":-", I
think), but also the difference between unexported and exported
(maybe possible by parsing "export -p", but I'd be shocked if that
doesn't run into portability problems).
Here's what I came up with, which does seem to work. It's pretty gnarly,
though.
-- >8 --
# possible without a sub-program?
# portability issues with no-newline and sed?
shellquote () {
printf "'"
printf '%s' "$1" | sed "s/'/'\\\\''/g"
printf "'"
}
# is there a simpler way, even when the contents are "unset"?
is_unset () {
eval "test -z \"\${$1}\" && test unset = \"\${$1-unset}\""
}
# probably not portable; also, possible without sub-program?
is_exported () {
export -p | grep "^declare -x $1="
}
# just a syntactic convenience
add_to () {
eval "$1=\"\$$1
\$2\""
}
fake_env () {
fake_env_restore_=
while test $# -gt 0
do
case "$1" in
*=*)
# this whole thing is not safe when the var name has
# spaces or other meta-characters, but since the names
# all come from our test scripts, that should be OK
fake_env_var_=${1%%=*}
eval "fake_env_orig_=\$$fake_env_var_"
fake_env_val_=${1#*=}
shift
# unset value and clear export flag...
add_to fake_env_restore_ "unset $fake_env_var_"
# ...and then restore what was there, if anything
if ! is_unset "$fake_env_var_"
then
add_to fake_env_restore_ \
"$fake_env_var_=$(shellquote
"$fake_env_orig_")"
if is_exported "$fake_env_var_"
then
add_to fake_env_restore_ \
"export $fake_env_var_"
fi
fi
eval "$fake_env_var_=$(shellquote "$fake_env_val_")"
eval "export $fake_env_var_"
;;
*)
"$@"
fake_env_ret_=$?
eval "$fake_env_restore_"
return $fake_env_ret_
;;
esac
done
}
# simple exercise
show() {
echo >&2 "$1: myvar=$myvar"
}
myvar="horrible \"\\' mess"
show before
fake_env myvar="temporary $myvar" show during
show after
-Peff
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