ln 軟體連結目錄時，當連結檔案已經存在時，結果非預期
建立軟體連結的語法如下：
link -s target linkName
例項：
ln -s ssh_connect_home link1
但是當我們想把此連結指向第二個檔案時，結果卻不如意料那般：
仔細一看：
原來這個命令將軟體連結建立到目錄中去了，這是為何？
參考一下man：
SYNOPSIS
ln [OPTION]... [-T] TARGET LINK_NAME (1st form)
ln [OPTION]... TARGET (2nd form)
ln [OPTION]... TARGET... DIRECTORY (3rd form)
ln [OPTION]... -t DIRECTORY TARGET... (4th form)
DESCRIPTION
In the 1st form, create a link to TARGET with the name LINK_NAME. In the 2nd form, create a link to TARGET in the current directory. In the 3rd and 4th forms, create links to each TARGET in
DIRECTORY. Create hard links by default, symbolic links with --symbolic. By default, each destination (name of new link) should not already exist. When creating hard links, each TARGET must
exist. Symbolic links can hold arbitrary text; if later resolved, a relative link is interpreted in relation to its parent directory.
原來，當連結檔案已經存在時，被解析成了第三種格式，會在資料夾中建立到每個target的連結（連結名使用檔名）。
解決方法：
使用-n選項。
-n, --no-dereference
treat LINK_NAME as a normal file if it is a symbolic link to a directory
如果target是檔案，則並不存在這種問題：
