> We could add it to the $sysparams hash provided by the zsh/system
module?

It just occurred to me that, with zsh/system, I can have the child process
send its pid as the first line of output.

Something like:

```
% zmodload zsh/system
% exec {FOO}< <(echo $sysparams[pid]; sleep 100; echo foo bar)
% read childpid <&$FOO # Get the pid, stored in $childpid
% cat <&$FOO # Handle the rest of the output
```

So it may not actually be necessary to add procsubstpid.

In fact, the approach above may be preferred if you need to get pids for
multiple process substitutions in one command (which I think is possible?).

Next question:

Is it possible to get the current subshell's pid without having to load the
zsh/system module ($sysparams param)? Bash seems to have the $BASHPID
variable. Is there anything like that in zsh core?

Or, alternatively, is it reasonable to assume that everyone will be able to
load the zsh/system module? Background here is that I had a user send a
pull request to zsh-autosuggestions requesting we don't depend on zsh/zpty
module since some people may not have it installed, so I'm trying to
minimize dependencies on non-core modules.

Eric Freese
303 875 2359

On Tue, Jun 12, 2018 at 5:32 AM, Peter Stephenson <p.stephenson@samsung.com>
wrote:

> On Mon, 11 Jun 2018 19:55:32 -0600
> Eric Freese <ericdfreese@gmail.com> wrote:
> > Do you know if there is any way to get the PID of the process spawned
> > for process substitution? It looks like `$!` doesn't hold it as it
> > does in bash.
>
> Hmm, this is obviously useful but I'd be loath simply to make $! do this
> as the fact there's an asynchronous process involved is a bit hidden and
> the mechanism is rather different from creating a background job, so
> that could be confusing.
>
> We could add it to the $sysparams hash provided by the zsh/system
> module?  This already contains some PID information.  (It's
> not strictly a system parameter but I don't think anyone's
> going to hold a gun to my head and tell me this hash can only
> return the result of immediate system calls.)
>
> pws
>
> diff --git a/Doc/Zsh/mod_system.yo b/Doc/Zsh/mod_system.yo
> index 7f2009b..a27bab4 100644
> --- a/Doc/Zsh/mod_system.yo
> +++ b/Doc/Zsh/mod_system.yo
> @@ -255,6 +255,11 @@ Returns the process ID of the parent of the current
> process, even in
>  subshells.  Compare tt($PPID), which returns the process ID of the parent
>  of the main shell process.
>  )
> +item(tt(procsubstpid))(
> +Returns the process ID of the last process started for process
> +substitution, i.e. the tt(<LPAR())var(...)tt(RPAR()) and
> +tt(>LPAR())var(...)tt(RPAR()) expansions.
> +)
>  enditem()
>  )
>  enditem()
> diff --git a/Src/Modules/system.c b/Src/Modules/system.c
> index 9fd4d25..7a4f4ee 100644
> --- a/Src/Modules/system.c
> +++ b/Src/Modules/system.c
> @@ -772,6 +772,8 @@ fillpmsysparams(Param pm, const char *name)
>         num = (int)getpid();
>      } else if (!strcmp(name, "ppid")) {
>         num = (int)getppid();
> +    } else if (!strcmp(name, "procsubstpid")) {
> +       num = (int)procsubstpid;
>      } else {
>         pm->u.str = dupstring("");
>         pm->node.flags |= PM_UNSET;
> @@ -805,6 +807,8 @@ scanpmsysparams(UNUSED(HashTable ht), ScanFunc func,
> int flags)
>      func(&spm.node, flags);
>      fillpmsysparams(&spm, "ppid");
>      func(&spm.node, flags);
> +    fillpmsysparams(&spm, "procsubstpid");
> +    func(&spm.node, flags);
>  }
>
>  static struct mathfunc mftab[] = {
> diff --git a/Src/exec.c b/Src/exec.c
> index 963b0a5..d445278 100644
> --- a/Src/exec.c
> +++ b/Src/exec.c
> @@ -174,6 +174,11 @@ mod_export int zleactive;
>  /**/
>  pid_t cmdoutpid;
>
> +/* pid of last process started by <(...),  >(...) */
> +
> +/**/
> +mod_export pid_t procsubstpid;
> +
>  /* exit status of process undergoing 'process substitution' */
>
>  /**/
> @@ -4850,6 +4855,7 @@ getproc(char *cmd, char **eptr)
>             return NULL;
>         if (!out)
>             addproc(pid, NULL, 1, &bgtime);
> +       procsubstpid = pid;
>         return pnam;
>      }
>      closem(FDT_UNUSED, 0);
> @@ -4887,6 +4893,7 @@ getproc(char *cmd, char **eptr)
>         {
>             addproc(pid, NULL, 1, &bgtime);
>         }
> +       procsubstpid = pid;
>         return pnam;
>      }
>      entersubsh(ESUB_ASYNC|ESUB_PGRP);
> @@ -4937,6 +4944,7 @@ getpipe(char *cmd, int nullexec)
>         }
>         if (!nullexec)
>             addproc(pid, NULL, 1, &bgtime);
> +       procsubstpid = pid;
>         return pipes[!out];
>      }
>      entersubsh(ESUB_PGRP);
> @@ -6172,6 +6180,7 @@ execsave(void)
>      es->cmdoutpid = cmdoutpid;
>      es->cmdoutval = cmdoutval;
>      es->use_cmdoutval = use_cmdoutval;
> +    es->procsubstpid = procsubstpid;
>      es->trap_return = trap_return;
>      es->trap_state = trap_state;
>      es->trapisfunc = trapisfunc;
> @@ -6207,6 +6216,7 @@ execrestore(void)
>      cmdoutpid = en->cmdoutpid;
>      cmdoutval = en->cmdoutval;
>      use_cmdoutval = en->use_cmdoutval;
> +    procsubstpid = en->procsubstpid;
>      trap_return = en->trap_return;
>      trap_state = en->trap_state;
>      trapisfunc = en->trapisfunc;
> diff --git a/Src/zsh.h b/Src/zsh.h
> index 8535d48..8e7f20b 100644
> --- a/Src/zsh.h
> +++ b/Src/zsh.h
> @@ -1095,6 +1095,7 @@ struct execstack {
>      pid_t cmdoutpid;
>      int cmdoutval;
>      int use_cmdoutval;
> +    pid_t procsubstpid;
>      int trap_return;
>      int trap_state;
>      int trapisfunc;
>
>