linux - 如何从后台进程 linux shell 脚本中获取结果？

Question

例如，假设我想计算 10 个大文件的行数并打印总数。

for f in files
do
    #this creates a background process for each file
    wc -l $f | awk '{print $1}' &
done

我正在尝试类似的事情:

for f in files
do
    #this does not work :/
    n=$( expr $(wc -l $f | awk '{print $1}') + $n ) &
done

echo $n

Answer 1

我终于找到了一个使用匿名管道和 bash 的可行解决方案:

#!/bin/bash

# this executes a separate shell and opens a new pipe, where the 
# reading endpoint is fd 3 in our shell and the writing endpoint
# stdout of the other process. Note that you don't need the 
# background operator (&) as exec starts a completely independent process.
exec 3< <(./a.sh 2&1)


# ... do other stuff


# write the contents of the pipe to a variable. If the other process
# hasn't already terminated, cat will block.
output=$(cat <&3)