NAME
source - Evaluate a file or resource as a Tcl scriptSYNOPSIS
source fileNamesource -rsrc resourceName ?fileName?
source -rsrcid resourceId ?fileName?
DESCRIPTION
This command takes the contents of the specified file or resource and passes it to the Tcl interpreter as a text script. The return value from source is the return value of the last command executed in the script. If an error occurs in evaluating the contents of the script then the source command will return that error. If a return command is invoked from within the script then the remainder of the file will be skipped and the source command will return normally with the result from the return command.
The -rsrc and -rsrcid forms of this command are only available on Macintosh computers. These versions of the command allow you to source a script from a TEXT resource. You may specify what TEXT resource to source by either name or id. By default Tcl searches all open resource files, which include the current application and any loaded C extensions. Alternatively, you may specify the fileName where the TEXT resource can be found.
source命令：
source命令也称为“点命令”，也就是一个点符号（.）,是bash的内部命令。
功能：使Shell读入指定的Shell程序文件并依次执行文件中的所有语句
source命令通常用于重新执行刚修改的初始化文件，使之立即生效，而不必注销并重新登录。
用法：
source filename 或 . filename
source命令(从 C Shell 而来)是bash shell的内置命令;点命令(.)，就是个点符号(从Bourne Shell而来)是source的另一名称。
source filename 与 sh filename 及./filename执行脚本的区别在那里呢？
1.当shell脚本具有可执行权限时，用sh filename与./filename执行脚本是没有区别得。./filename是因为当前目录没有在PATH中，所有"."是用来表示当前目录的。
2.sh filename 重新建立一个子shell，在子shell中执行脚本里面的语句，该子shell继承父shell的环境变量，但子shell新建的、改变的变量不会被带回父shell，除非使用export。
3.source filename：这个命令其实只是简单地读取脚本里面的语句依次在当前shell里面执行，没有建立新的子shell。那么脚本里面所有新建、改变变量的语句都会保存在当前shell里面