bash从一个函数中设置多个变量的方法

Question

我想用更自上而下的设计编写一个shell脚本。我曾经用Kornshell脚本来做这件事。我定义了可以返回多组变量的各种函数(例如，getopts函数)。然后，我可以在主程序中使用这些函数来设置我想要的变量。

不幸的是，BASH和Kornshell在处理这个例子的方式上似乎存在分歧。这是我在Kornshell中运行的一个简单脚本。我的函数foo返回四个值。我将在我的主程序中把这四个值读入变量：

#!/bin/ksh
function foo {
echo "this:that:the:other"
}
IFS=":"
foo | read one two three four
echo "one = $one"
echo "two = $two"
echo "three = $three"
echo "four = $four"

这产生：

one = this
two = that
three = the
four = other

工作起来很有魅力。让我们使用BASH而不是Kornshell:来尝试相同的程序

#!/bin/bash
function foo {
echo "this:that:the:other"
}
IFS=":"
foo | read one two three four
echo "one = $one"
echo "two = $two"
echo "three = $three"
echo "four = $four"

这产生：

one = 
two = 
three = 
four = 

通往阅读的管道根本不起作用。让我们作为来尝试一下，这里是阅读：

#!/bin/bash
function foo {
echo "this:that:the:other"
}
IFS=":"
read one two three four<<<$(foo)
echo "one = $one"
echo "two = $two"
echo "three = $three"
echo "four = $four"

我得到：

one = this that the other
two =
three =
four =

这允许设置$one，但不允许设置其他变量。奇怪的是，冒号被从字符串中删除了。让我们从返回值中删除冒号：

#!/bin/bash
function foo {
echo "this that the other"
}
read  one two three four<<<$(foo)
echo "one = $one"
echo "two = $two"
echo "three = $three"
echo "four = $four"
one = this
two = that
three = the
four = other

这确实有效。每个变量都是从函数foo中读入的。

我做错了什么？为什么设置IFS似乎不像我在BASH中认为的那样工作？或者有更好的方法吗？

Answer 1

您必须引用：

#!/bin/bash
function foo {
echo "this:that:the:other"
}
IFS=":"
read one two three four<<<"$(foo)"
^      ^

执行时返回：

$ ./a
one = this
two = that
three = the
four = other

---

关于这个不起作用：

#!/bin/bash
...    
IFS=":"
foo | read one two three four
echo "one = $one"

我想这是因为IFS是在一个不同于具有read的shell中定义的。此外，将foo管道传输到read似乎不是在bash中向read提供字符串的方式。

为此，打开一个新的shell，如Bash脚本所示，从stdin管道读取值：

$ foo | { IFS=":"; read one two three four; echo "one = $one"; echo "two = $two"; echo "three = $three"; echo "four = $four"; }
one = this
two = that
three = the
four = other

Answer 2

如果不使用read，这也将在bash和ksh:中工作

IFS=: && set -- `foo`
echo "one = $1"
echo "two = $2"
echo "three = $3"
echo "four = $4"

bts这也适用于BASH，而不创建子shell：

function foo {
echo "this:that:the:other"
}
IFS=":" read one two three four < <(foo)
echo "one = $one"
echo "two = $two"
echo "three = $three"
echo "four = $four"