BASH：只有当函数通过管道传输时，全局变量才可以在函数中更新（简单示例）
这听起来有问题，但可能有人可以解释它：
以下脚本不起作用，输出如下：
#!/bin/bash
GLOBAL_VAR="OLD"
myfunc() {
echo "func before set> $GLOBAL_VAR"
GLOBAL_VAR="NEW"
echo "func after set> $GLOBAL_VAR"
}
myfunc | cat
echo "final value> $GLOBAL_VAR"
输出：
func before set> OLD
func after set> NEW
final value> OLD
现在，只需取下 | cat ，它起作用了！
#!/bin/bash
GLOBAL_VAR="OLD"
myfunc() {
echo "func before set> $GLOBAL_VAR"
GLOBAL_VAR="NEW"
echo "func after set> $GLOBAL_VAR"
}
myfunc
echo "final value> $GLOBAL_VAR"
输出：
func before set> OLD
func after set> NEW
final value> NEW
This smells buggy, but probably, someone can explain it:
The following script doesn't work, the output is below:
#!/bin/bash
GLOBAL_VAR="OLD"
myfunc() {
echo "func before set> $GLOBAL_VAR"
GLOBAL_VAR="NEW"
echo "func after set> $GLOBAL_VAR"
}
myfunc | cat
echo "final value> $GLOBAL_VAR"
Output:
func before set> OLD
func after set> NEW
final value> OLD
Now, just take off the | cat and it works!
#!/bin/bash
GLOBAL_VAR="OLD"
myfunc() {
echo "func before set> $GLOBAL_VAR"
GLOBAL_VAR="NEW"
echo "func after set> $GLOBAL_VAR"
}
myfunc
echo "final value> $GLOBAL_VAR"
Output:
func before set> OLD
func after set> NEW
final value> NEW
如果你对这篇内容有疑问，欢迎到本站社区发帖提问 参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。
绑定邮箱获取回复消息
由于您还没有绑定你的真实邮箱，如果其他用户或者作者回复了您的评论，将不能在第一时间通知您！
发布评论
评论（1）
管道创建子外壳。 bash 手册中指出，子 shell 无法修改其环境父母。请参阅以下链接：
http://www.gnu.org/software/bash/manual/bashref。 html#Pipelines
http://wiki.bash-hackers.org/scripting/processtree#actions_that_create_a_subshell
A pipe creates a subshell. It's said in the bash manual that subshells cannot modify the environment of their parents. See these links:
http://www.gnu.org/software/bash/manual/bashref.html#Pipelines
http://wiki.bash-hackers.org/scripting/processtree#actions_that_create_a_subshell