zsh typically runs the final command in a pipeline in the main shell
instead of a subshell. However, POSIX requires that all commands in a
pipeline run in a subshell, but permits zsh's behavior as an extension.
Since zsh may be used as /bin/sh in some cases (such as macOS Catalina),
it makes sense to have the POSIX behavior when emulating sh, so do that
by checking for being the final item of a multi-item pipeline and
creating a subshell in that case.
>From the comment above execpline(), we know the following:
last1 is a flag that this command is the last command in a shell that
is about to exit, so we can exec instead of forking. It gets passed
all the way down to execcmd() which actually makes the decision. A 0
is always passed if the command is not the last in the pipeline. […]
If last1 is zero but the command is at the end of a pipeline, we pass
2 down to execcmd().
So there are three cases to consider in this code:
• last1 is 0, which means we are not at the end of a pipeline, in which
case we should not change behavior.
• last1 is 1, which means we are effectively running in a subshell,
because nothing that happens due to the exec is going to affect the
actual shell, since it will have been replaced. So there is nothing
to do here.
• last1 is 2, which means our command is at the end of the pipeline, so
in sh mode we should create a subshell by forking.
input is nonzero if the input to this process is a pipe that we've
opened. At the end of a multi-stage pipeline, it will necessarily be
nonzero.
Note that several of the tests may appear bizarre, since most developers
do not place useless variable assignments directly at the end of a
pipeline. However, as the function tests demonstrate, there are cases
where assignments may occur when a shell function is used at the end of
a command. The remaining assignment tests simply test additional cases,
such as the use of local, that would otherwise be untested.
---
Src/exec.c | 10 ++++++----
Test/B07emulate.ztst | 22 ++++++++++++++++++++++
2 files changed, 28 insertions(+), 4 deletions(-)
diff --git a/Src/exec.c b/Src/exec.c
index 29f4fc5ca..f2650f311 100644
--- a/Src/exec.c
+++ b/Src/exec.c
@@ -2866,11 +2866,13 @@ execcmd_exec(Estate state, Execcmd_params eparams,
pushnode(args, dupstring("fg"));
}
- if ((how & Z_ASYNC) || output) {
+ if ((how & Z_ASYNC) || output ||
+ (last1 == 2 && input && EMULATION(EMULATE_SH))) {
/*
- * If running in the background, or not the last command in a
- * pipeline, we don't need any of the rest of this function to
- * affect the state in the main shell, so fork immediately.
+ * If running in the background, not the last command in a
+ * pipeline, or the last command in a multi-stage pipeline
+ * in sh mode, we don't need any of the rest of this function
+ * to affect the state in the main shell, so fork immediately.
*
* In other cases we may need to process the command line
* a bit further before we make the decision.
diff --git a/Test/B07emulate.ztst b/Test/B07emulate.ztst
index 7b1592fa9..45c39b51d 100644
--- a/Test/B07emulate.ztst
+++ b/Test/B07emulate.ztst
@@ -276,3 +276,25 @@ F:Some reserved tokens are handled in alias expansion
0:--emulate followed by other options
>yes
>no
+
+ emulate sh -c '
+ foo () {
+ VAR=foo &&
+ echo $VAR | bar &&
+ echo "$VAR"
+ }
+ bar () {
+ tr f b &&
+ VAR="$(echo bar | tr r z)" &&
+ echo "$VAR"
+ }
+ foo
+ '
+ emulate sh -c 'func() { echo | local def="abc"; echo $def;}; func'
+ emulate sh -c 'abc="def"; echo | abc="ghi"; echo $abc'
+0:emulate sh uses subshell for last pipe entry
+>boo
+>baz
+>foo
+>
+>def
