Fix unexpected behavior for bash/ash

[zzjjbb]

When a folder name contains [ ], the ${a#$b} will not work as expected (tested on bash/ash/zsh, and the first 2 cannot work. However, zsh can work)

Example

bash/ash

a="/[1]/2.txt"
b="/[1]/"
echo "${a#$b}"
echo "${a#"$b"}"
# output:
# /[1]/2.txt
# 2.txt

zsh

a="/[1]/2.txt"
b="/[1]/"
echo "${a#$b}"
echo "${a#"$b"}"
# output:
# 2.txt
# 2.txt

之所以发现这个隐蔽的问题，是因为：

我用那个aria2pro docker下载多个大文件到同一个文件夹，文件夹名字大概是这样的[210522] Folder Name，结果rclone的时候网速跑的飞快，CPU也占满，但是很久才能完成，有时还有hash check error的错误，查看统计信息container的输出流量竟然是输入流量的数倍。最后发现是rclone是对整个目录进行move的，多个文件就同时move了多次，各种冲突。而且测试的时候怎么都没问题，正式下载就出错。查了半天才发现是这个中括号的问题:rage: 之前没有怎么用过Linux shell，一开始啥也看不懂。。。

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[P3TERX]

感谢！