On Wed, Sep 7, 2022 at 2:44 PM Michaël Cadilhac <michael@cadilhac.name>
wrote:

> $ while :; do read; echo | xclip; echo loop; done
>

Bash executes the left side of a pipeline in the current shell and the
right side in a forked subshell.  Zsh does the opposite, which means xclip
is a process group leader with access to the terminal.

xclip itself then forks and clones a copy which continues running.  That
copy has control of the terminal, which causes "read" to see an I/O error
and immediately fail.  You can see read exiting failure if you change the
loop to be
    while :; do read; echo $?; echo | xclip; echo loop; done

You're not testing the return value of read, so the shell goes on to the
next statement and the effect repeats.  Each new xclip causes the previous
xclip to exit (cf. xclip -l option) by grabbing the selection, so you never
run out of processes.