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![]() zsh typically runs the final command in a pipeline in the main shell instead of a subshell. However, POSIX specifies that all commands in a pipeline run in a subshell, but permits zsh's behavior as an extension. The default /bin/sh implementations on various Linux distros and the BSDs always use a subshell for all components of a pipeline. Since zsh may be used as /bin/sh in some cases (such as macOS Catalina), it makes sense to have the common sh 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. |
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.. | ||
Builtins | ||
Modules | ||
Zle | ||
.cvsignore | ||
.distfiles | ||
.exrc | ||
.indent.pro | ||
builtin.c | ||
compat.c | ||
cond.c | ||
context.c | ||
exec.c | ||
glob.c | ||
hashnameddir.c | ||
hashtable.c | ||
hashtable.h | ||
hist.c | ||
init.c | ||
input.c | ||
jobs.c | ||
lex.c | ||
linklist.c | ||
loop.c | ||
main.c | ||
Makefile.in | ||
Makemod.in.in | ||
makepro.awk | ||
math.c | ||
mem.c | ||
mkbltnmlst.sh | ||
mkmakemod.sh | ||
modentry.c | ||
module.c | ||
openssh_bsd_setres_id.c | ||
options.c | ||
params.c | ||
parse.c | ||
pattern.c | ||
prompt.c | ||
prototypes.h | ||
signals.c | ||
signals.h | ||
signames1.awk | ||
signames2.awk | ||
sort.c | ||
string.c | ||
subst.c | ||
text.c | ||
utils.c | ||
watch.c | ||
wcwidth9.h | ||
zsh.h | ||
zsh.ico | ||
zsh.mdd | ||
zsh.rc | ||
zsh_system.h | ||
ztype.h |