在使用一些命令时（如：ls、git），刚好遇到一些需求是想很方便地遍历所有的目录和文件，后来经过搜索，终于找到了一个“神奇”的通配符“**”（两个星号），在设置了Bash的globstar选项后，**就可以匹配任当前何目录（包括子目录）以及其中的文件。所以，了解了一下globstar这个选项，当未设置globstar时，**通配符的作用和*是相同的，而设置了globstar后，**的匹配范围不同了（更广一些）。注意：globstar是Bash 4.0才引入的选项，之前的老版本是不支持的，使用“bash –version”可产看当前使用的Bash的版本。

关于glob这个词，我也觉得好奇，中文不好解释，大致就是“对通配符展开”的意思，如下的英文吧：
In shell-speak, globbing is what the shell does when you use a wildcard in a command (e.g. * or ?). Globbing is matching the wildcard pattern and returning the file and directory names that match and then replacing the wildcard pattern in the command with the matched items.

在bash的man page中，对globstar的说明提到只两次，说的都是同一件事情，如下：

Pathname Expansion
......
*      Matches any string, including the null string.  When the globstar shell option is enabled,  and  *  is
              used  in  a  pathname expansion context, two adjacent *s used as a single pattern will match all files
              and zero or more directories and subdirectories.  If followed by a /, two adjacent *s will match  only
              directories and subdirectories.
......
globstar
        If set, the pattern ** used in a pathname expansion context will match a files and zero or more directories
        and subdirectories.  If the pattern is followed by a /, only directories and subdirectories match.

写了个测试和学习globstar的shell脚本如下：

#!/bin/bash
<pre lang="Bash">
function show()
{
        for i in **
        do
                echo $i
        done
}
               
cd /root/jay/
echo "------------------------"
echo "disable globstar option:"
# globstar is disabled by default
shopt -u globstar
show
echo "------------------------"
echo "enable globstar option:"
shopt -s globstar
show

执行上面测试globstar的shell脚本，看它的输出结果，就很容易理解globstar了，如下：

[root@smilejay jay]# ./test_globstar.sh
------------------------
disable globstar option:
dir1
dir2
file1
file2
index.html
test_shopt.sh
------------------------
enable globstar option:
dir1
dir1/file3
dir2
dir2/file4
file1
file2
index.html
test_shopt.sh

参考资料：

http://www.linuxjournal.com/content/globstar-new-bash-globbing-option

bash4引入的新feature：http://wiki.bash-hackers.org/bash4

http://wiki.bash-hackers.org/syntax/expansion/globs