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Re: "echo | ps -j $(:) | cat | cat | cat" runs components in different process groups
- X-seq: zsh-workers 42528
- From: Stephane Chazelas <stephane.chazelas@xxxxxxxxx>
- To: Zsh hackers list <zsh-workers@xxxxxxx>
- Subject: Re: "echo | ps -j $(:) | cat | cat | cat" runs components in different process groups
- Date: Sun, 25 Mar 2018 08:38:53 +0100
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2018-03-23 16:16:13 +0000, Stephane Chazelas:
> - the first pipeline component must be a builtin or compound command
To clarify, as explained by Bart, it doesn't have to be builtin.
It's more easily reproducible with builtins as they exit quickly
but one just needs a command that exits before the command
substitution as in:
sleep 1 | ps -j $(sleep 2) | cat|cat|cat...
Another side effect is that
echo test | tee $(uname) | sleep 10 | cat
cannot be aborted with ^C as only "cat" is in foreground (echo
gone, tee (soon gone too) and sleep on their own process group).
Also, ^Z suspends cat only causing a deadlock.
That's probably a worse problem and could explain the similar
lock ups I sometimes experience in zsh.
> - the second component must have a command substitution in the
> arguments (OK when in targets of redirections).
Following-up on my previous email, that means:
$ n=1; echo $((++n)) | cat; echo $n
$ n=1; echo > $((++n)) | cat; echo $n
Which looks a bit inconsistent.
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