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：
|
1 2 3 4 5 6 7 8 9 10 |
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：
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 |
#!/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：
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 |
[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