while read loop with input from process substitution not exiting on break in zsh答案

【问题标题】：while read loop with input from process substitution not exiting on break in zshwhile read loop with input from process substitution not exiting on break in zsh
【发布时间】：2022-12-01 15:38:24
【问题描述】：

Using zsh, I was trying to break the while loop after file move event, but break happens only after the second one. This only occurs when I try to execute script

#!/bin/zsh

while read changed; do
  echo $changed
  if [ $changed = MOVE_SELF ]; then
    echo "File was moved."
    break
  fi
done < <(inotifywait -m -e move_self --format "%e" $1)

echo "HI THERE"

in zsh. However, if I try the same code with #!/bin/bash it works as expected (loop breaks after the first event).

【问题讨论】：

I'd suggest tagging this only zsh and not bash; the bash behavior is well-understood, so you need only zsh experts looking at this question, not bash experts.
@rowboat, Thank you. <(... &) works fine. Would you mind writing an answer? I need -m, example above is simplified.
请问为什么进程替换有两个<标志，即done < <(inotify ...)？我本以为只有一个。
@user1934428，看看这个：stackoverflow.com/a/28927847/15036204

标签： zsh process-substitution

【解决方案1】：

Behavior in zsh and bash is different. One of the possible solutions is to use & for command in process substitution. Diff:

< done < <(inotifywait -m -e move_self --format "%e" $1)
---
> done < <(inotifywait -m -e move_self --format "%e" $1 &)

Looks like zsh is blocking waits for process substitution to execute again. Output of zsh -x after first execution of inotitywait without &:

+script.sh:3> read -r changed
+script.sh:3> inotifywait -m -e move_self --format %e file.lua
Setting up watches.
Watches established.
+script.sh:4> echo MOVE_SELF
MOVE_SELF
+script.sh:5> [ MOVE_SELF '=' MOVE_SELF ']'
+script.sh:6> echo 'File was moved.'
File was moved.
+script.sh:7> break

【讨论】：