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“while”循环中奇怪的变量行为

tag-icon • tag-icon shell-script shell subshell
“while”循环中奇怪的变量行为

有人可以向我解释一下这是怎么回事吗？

脚本：

#!/bin/sh
SKIP="unity-launcher|unity-panel|unity-dash|Hud|XdndCollectionWindowImp|Desktop"
WINS=()
wmctrl -l | grep -Ev " (${SKIP})" | cut -d \  -f 1 | while read window; do
    WINS=( ${WINS[@]} $window )
    echo "Found window: $window; New size: ${#WINS[@]}"
done
echo "Total window count: ${#WINS[@]}"
echo "Window IDs:"
for i in "${WINS[@]}"; do
    echo "  $i"
done

输出：

Found window: 0x0380000a; New size: 1
Found window: 0x038002ae; New size: 2
Found window: 0x03800a33; New size: 3
Found window: 0x03000001; New size: 4
Found window: 0x04c00004; New size: 5
Total window count: 0
Window IDs:

预期的：

Found window: 0x0380000a; New size: 1
Found window: 0x038002ae; New size: 2
Found window: 0x03800a33; New size: 3
Found window: 0x03000001; New size: 4
Found window: 0x04c00004; New size: 5
Total window count: 5
Window IDs:
    0x0380000a
    0x038002ae
    0x03800a33
    0x03000001
    0x04c00004

本质上，在循环结束时while，WINS数组以某种方式被重置，我不知道为什么。 bash 中是否有一些我不知道的奇怪的作用域？

答案1

管道创建子 shell，这些子 shell 无法更改其上方进程中的值。尝试：

while read window; do
    WINS=( ${WINS[@]} $window )
    echo "Found window: $window; New size: ${#WINS[@]}"
done < <(wmctrl -l | grep -Ev " (${SKIP})" | cut -d \  -f 1)

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