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git://git.code.sf.net/p/zsh/code
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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 | ||