[求助]关于进程替换的问题

DViewer

在网站上看到了下面这段代码,输出为HI THERE , 不理解，哪位大神能解释一下，尤其是 这个符号 “=>”
f() {
    cat "$1" >"$x"
}

x=>(tr '[:lower:]' '[:upper:]') f <(echo 'hi there')

r2007

=是单独的，>()这个是一组

bikkuri

执行的效果应该和echo 'hi there'|tr '[:lower:]' '[:upper:]'一样。
把楼主的代码改成：

1. f() {
   
2.      cat "$1" >"$x"
   
3. echo "\$1=$1"
   
4. echo "\$x=$x"
   
5. }
   
6. 
   
7. x=>(tr '[:lower:]' '[:upper:]') f <(echo 'hi there')

复制代码

然后执行结果为：

1. $1=/dev/fd/63
   
2. $x=/dev/fd/62
   
3. HI THERE

复制代码

也就是把文件描述符63的内容重定向到文件描述符62去了。

DViewer

谢谢两位的解答，我还是没有理解，主要是变量x。
关于这段代码有段说明

Scope


If a process substitution is expanded as an argument to a function, expanded to an environment variable during calling of a function, or expanded to any assignment within a function, the process substitution will be "held open" for use by any command within the function or its callees, until the function in which it was set returns. If the same variable is set again within a callee, unless the new variable is local, the previous process substitution is closed and will be unavailable to the caller when the callee returns.

In essence, process substitutions expanded to variables within functions remain open until the function in which the process substitution occured returns - even when assigned to locals that were set by a function's caller. Dynamic scope doesn't protect them from closing.




This example demonstrates how process substitutions can be made to resemble "passable" objects. This results in converting the output of f's argument to uppercase.

f() {
    cat "$1" >"$x"
}

x=>(tr '[:lower:]' '[:upper:]') f <(echo 'hi there')
See the above section on scope


来自 http://wiki.bash-hackers.org/syntax/expansion/proc_subst

关于作用范围的那段没有看懂