Bash模式返回标量和数组值对象:

定义

url_parse() { # parse 'url' into: 'url_host', 'url_port', ...
   local "$@" # inject caller 'url' argument in local scope
   local url_host="..." url_path="..." # calculate 'url_*' components
   declare -p ${!url_*} # return only 'url_*' object fields to the caller
}

调用

main() { # invoke url parser and inject 'url_*' results in local scope
   eval "$(url_parse url=http://host/path)" # parse 'url'
   echo "host=$url_host path=$url_path" # use 'url_*' components
}

提醒薇姬·罗嫩，考虑一下下面的代码

function use_global
{
    eval "$1='changed using a global var'"
}

function capture_output
{
    echo "always changed"
}

function test_inside_a_func
{
    local _myvar='local starting value'
    echo "3. $_myvar"

    use_global '_myvar'
    echo "4. $_myvar"

    _myvar=$( capture_output )
    echo "5. $_myvar"
}

function only_difference
{
    local _myvar='local starting value'
    echo "7. $_myvar"

    local use_global '_myvar'
    echo "8. $_myvar"

    local _myvar=$( capture_output )
    echo "9. $_myvar"
}

declare myvar='global starting value'
echo "0. $myvar"

use_global 'myvar'
echo "1. $myvar"

myvar=$( capture_output )
echo "2. $myvar"

test_inside_a_func
echo "6. $_myvar" # this was local inside the above function

only_difference

将会给

0. global starting value
1. changed using a global var
2. always changed
3. local starting value
4. changed using a global var
5. always changed
6. 
7. local starting value
8. local starting value
9. always changed

也许正常的场景是使用test_inside_a_func函数中使用的语法，因此在大多数情况下可以同时使用这两种方法，尽管捕获输出是在任何情况下都能工作的更安全的方法，它模仿在其他语言中可以找到的函数的返回值，Vicky Ronnen正确地指出了这一点。

agt@agtsoft:~/temp$ cat ./fc 
#!/bin/sh

fcall='function fcall { local res p=$1; shift; fname $*; eval "$p=$res"; }; fcall'

function f1 {
    res=$[($1+$2)*2];
}

function f2 {
    local a;
    eval ${fcall//fname/f1} a 2 3;
    echo f2:$a;
}

a=3;
f2;
echo after:a=$a, res=$res

agt@agtsoft:~/temp$ ./fc
f2:10
after:a=3, res=

你可以使用一个全局变量:

declare globalvar='some string'

string ()
{
  eval  "$1='some other string'"
} # ----------  end of function string  ----------

string globalvar

echo "'${globalvar}'"

这给了

'some other string'

没有比这更好的方法了。Bash只知道写入标准输出的状态码(整数)和字符串。

最直接和健壮的解决方案是使用命令替换，就像其他人写的那样:

assign()
{
    local x
    x="Test"
    echo "$x"
}

x=$(assign) # This assigns string "Test" to x

缺点是性能，因为这需要一个单独的过程。

本主题中建议的另一种技术，即传递要赋值的变量的名称作为参数，有副作用，我不推荐它的基本形式。问题是，你可能需要函数中的一些变量来计算返回值，可能发生的情况是，用于存储返回值的变量的名称会干扰其中一个:

assign()
{
    local x
    x="Test"
    eval "$1=\$x"
}

assign y # This assigns string "Test" to y, as expected

assign x # This will NOT assign anything to x in this scope
         # because the name "x" is declared as local inside the function

当然，您可以不将函数的内部变量声明为局部变量，但您确实应该始终这样做，否则另一方面，如果存在同名的父作用域，则可能会意外地覆盖父作用域中不相关的变量。

一个可能的解决方法是显式声明传递的变量为全局变量:

assign()
{
    local x
    eval declare -g $1
    x="Test"
    eval "$1=\$x"
}

If name "x" is passed as an argument, the second row of the function body will overwrite the previous local declaration. But the names themselves might still interfere, so if you intend to use the value previously stored in the passed variable prior to write the return value there, be aware that you must copy it into another local variable at the very beginning; otherwise the result will be unpredictable! Besides, this will only work in the most recent version of BASH, namely 4.2. More portable code might utilize explicit conditional constructs with the same effect:

assign()
{
    if [[ $1 != x ]]; then
      local x
    fi
    x="Test"
    eval "$1=\$x"
}

也许最优雅的解决方案是为函数返回值和保留一个全局名称 在您编写的每个函数中一致地使用它。