On Tue, May 31, 2016 at 11:44:13PM -0400, Jeff King wrote:
> So this is gross, but I think it actually _is_ portable, with the
> exception of the "is it exported" check.
Hmm. So after thinking on this, I realized we don't have to do the
clean-up ourselves at all, if we simply operate in a subshell. That
means that any shell functions we call couldn't mutate the state, but
that's probably an acceptable compromise, if the goal is to behave like
env except for being able to call shell functions.
Here is the "final" version of the more complicated scheme I came up
with. That I think should be fairly portable, but the subshell thing is
probably way less gross.
-- >8 --
test_var_is_set () {
eval "test -n \"\${$1+set}\""
}
test_var_is_exported () {
sh -c "test -n \"\${$1+set}\""
}
# set var named by $1 to contents of $2
test_set_var () {
eval "$1=\$2"
}
# set var named by $1 to contents of var named by $2
test_copy_var () {
eval "test_set_var \$1 \"\$$2\""
}
# just a syntactic convenience
add_to () {
eval "$1=\"\$$1
\$2\""
}
test_env () {
test_env_restore_=
while test $# -gt 0
do
case "$1" in
*=*)
# this whole thing is not safe when the var name has
# spaces or other meta-characters, but since the names
# all come from our test scripts, that should be OK
test_env_var_=${1%%=*}
test_env_orig_=test_env_orig_$test_env_var_
test_copy_var $test_env_orig_ $test_env_var_
test_env_val_=${1#*=}
shift
# unset value and clear export flag...
add_to test_env_restore_ "unset $test_env_var_"
# ...and then restore what was there, if anything
if test_var_is_set "$test_env_var_"
then
add_to test_env_restore_ \
"test_copy_var $test_env_var_ $test_env_orig_"
if test_var_is_exported "$test_env_var_"
then
add_to test_env_restore_ \
"export $test_env_var_"
fi
fi
# and then clean up our temp variable
add_to test_env_restore_ "unset $test_env_orig_"
test_set_var $test_env_var_ "$test_env_val_"
eval "export $test_env_var_"
;;
*)
"$@"
test_env_ret_=$?
eval "$test_env_restore_"
return $test_env_ret_
;;
esac
done
}
# simple exercise
show () {
echo >&2 "$1: here=$myvar ${myvar+(set)} sub=$(sh -c 'echo "$myvar ${myvar+(set)}"')"
}
doit () {
echo "==> $1"
show before
test_env myvar="temporary $myvar" show during
show after
}
unset myvar
doit unset
myvar="horrible \"\\' mess"
doit with-value
export myvar
doit exported-with-value
myvar=
export myvar
doit exported-but-blank
--
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