从 shell 脚本中的被调用函数返回值 [英] Returning value from called function in a shell script

问题描述

我想从 shell 脚本中调用的函数返回值.也许我缺少语法.我尝试使用全局变量.但这也行不通.代码是:

I want to return the value from a function called in a shell script. Perhaps I am missing the syntax. I tried using the global variables. But that is also not working. The code is:

lockdir="somedir"
test() {
    retval=""

    if mkdir "$lockdir"
        then    # Directory did not exist, but it was created successfully
            echo >&2 "successfully acquired lock: $lockdir"
            retval="true"
        else
            echo >&2 "cannot acquire lock, giving up on $lockdir"
            retval="false"
    fi
    return retval
}


retval=test()
if [ "$retval" == "true" ]
    then
        echo "directory not created"
    else
        echo "directory already created"
fi

推荐答案

Bash 函数不能像您希望的那样直接返回字符串.你可以做三件事:

A Bash function can't return a string directly like you want it to. You can do three things:

1. 回显一个字符串
2. 返回一个退出状态，它是一个数字，而不是一个字符串
3. 共享变量

其他一些 shell 也是如此.

This is also true for some other shells.

以下是执行每个选项的方法:

Here's how to do each of those options:

lockdir="somedir"
testlock(){
    retval=""
    if mkdir "$lockdir"
    then # Directory did not exist, but it was created successfully
         echo >&2 "successfully acquired lock: $lockdir"
         retval="true"
    else
         echo >&2 "cannot acquire lock, giving up on $lockdir"
         retval="false"
    fi
    echo "$retval"
}

retval=$( testlock )
if [ "$retval" == "true" ]
then
     echo "directory not created"
else
     echo "directory already created"
fi

2.返回退出状态

lockdir="somedir"
testlock(){
    if mkdir "$lockdir"
    then # Directory did not exist, but was created successfully
         echo >&2 "successfully acquired lock: $lockdir"
         retval=0
    else
         echo >&2 "cannot acquire lock, giving up on $lockdir"
         retval=1
    fi
    return "$retval"
}

testlock
retval=$?
if [ "$retval" == 0 ]
then
     echo "directory not created"
else
     echo "directory already created"
fi

3.共享变量

lockdir="somedir"
retval=-1
testlock(){
    if mkdir "$lockdir"
    then # Directory did not exist, but it was created successfully
         echo >&2 "successfully acquired lock: $lockdir"
         retval=0
    else
         echo >&2 "cannot acquire lock, giving up on $lockdir"
         retval=1
    fi
}

testlock
if [ "$retval" == 0 ]
then
     echo "directory not created"
else
     echo "directory already created"
fi

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