所以你将当前目录添加到Ruby的加载路径

参考文献：

>可从The Pragmatic Programmers Guide的此页面的“执行环境变量”部分找到

An array of strings,where each string specifies a directory to be searched for Ruby scripts and binary extensions used by the load and require methods. The initial value is the value of the arguments passed via the -I command-line option,followed by an installation-defined standard library location,followed by the current directory (“.”)[ObvIoUsly this link is for an older version of Ruby as this is still in there]. This variable may be set from within a program to alter the default search path; typically,programs use $: << dir to append dir to the path.

>可以在ruby-doc.org的docs for array中找到.

Append—Pushes the given object on to the end of this array. This expression returns the array itself,so several appends may be chained together.