Re: Command hangs when using process substitution

[Andreas Schwab]

On Nov 18 2023, Greg Wooledge wrote:

> On Sat, Nov 18, 2023 at 08:36:06AM -0500, dbarrett--- via Bug reports for the 
> GNU Bourne Again SHell wrote:
>> echo foo | tee >(xclip -i) | tr o x
>> 
>> The command does print "fxx" but then it hangs.
>> 
>> The same command behaves correctly when run in zsh.
>
> For the record, here's what processes are running on the terminal while
> it's in the "hanging" state:
>
> unicorn:~$ ps f -ft pts/28
> UID          PID    PPID  C STIME TTY      STAT   TIME CMD
> greg     1082506 1082504  0 09:21 pts/28   Ss     0:00 bash
> greg     1082862 1082506  0 09:35 pts/28   S+     0:00  \_ tr o x
> greg     1082864       1  0 09:35 pts/28   S+     0:00 xclip -i
>
> The tee process has exited, but somehow the tr process has not --
> which must mean that tr's stdin is still open.
>
> One additional observation: if I highlight something (e.g. that ps
> output), this causes the pipeline to terminate.  I assume the xclip
> process somehow notices the highlighting and exits, which causes
> tr to exit, because (presumably) it's the orphaned xclip process
> whose output was still connected to tr's input.

xclip puts itself into the background, unless it is called with -quiet
or -verbose.

       -silent
              fork  into the background to wait for requests, no informational
              output, errors only (default)

       -quiet show informational messages on the terminal and run in the fore-
              ground

       -verbose
              provide a running commentary of what xclip is doing

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
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