庆典词的拆分机制 [英] bash word splitting mechanism

问题描述

我是新来Bash和我看到有被Bash进行自动分词：

I am new to Bash and I am seeing that there is automatic word splitting done by Bash:

a="1  2     3 4"

如果我回声是由回声$ A 我 1 2 3 4 ，它已经做字分裂含蓄。如果通过一个我环，我分别得到1，2，3和4。

If I echo "a" by echo $a I got 1 2 3 4, which has done word splitting implicitly. If I loop through "a", I got 1, 2, 3, and 4 respectively.

我也是从这里是

外壳扫描参数扩展的结果，命令
  替换和算术扩展未发生内
  双引号的字分割。

The shell scans the results of parameter expansion, command substitution, and arithmetic expansion that did not occur within double quotes for word splitting.

而且我还发现，如果我有

And I also found that if I have

b=$a;
echo "$b"

我会得到

"1 2 3 4"

所以，这里是我的问题：当在分词做了什么？它改变字符串本身？当我使用它才生效回声或为（循环）？更一般的，如何处理bash的它在地球上？

So, here is my problem: when is the word splitting done? does it change the string itself? Does it only take effect when I use echo or for (loop)? More general, how does bash handle it on earth?

十分感谢！

推荐答案

读男人庆典。对于分配，它说：

所有的值进行波浪线扩展，参数和变量扩展，命令替换，算术扩展和引用删除[...]在特殊参数下解释不进行词的拆分，以$ @的例外。不执行路径扩展。

All values undergo tilde expansion, parameter and variable expansion, command substitution, arithmetic expansion, and quote removal [ ... ] Word splitting is not performed, with the exception of "$@" as explained below under Special Parameters. Pathname expansion is not performed.

词的拆分也在 [[]] 情况不会发生：

Word splitting also does not happen in [[ ]] conditions:

词的拆分和路径的扩展之间不上话进行的[[和]]

Word splitting and pathname expansion are not performed on the words between the [[ and ]]

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