source 或者 .

 .  filename [arguments] ------ 点后面有个空格符。
source filename [arguments]
              Read and execute commands from filename in the current shell environment and return the exit status of the last  command  exe-
              cuted from filename.  If filename does not contain a slash, file names in PATH are used to find the directory containing file-
              name.  The file searched for in PATH need not be executable.  When bash is  not  in  posix  mode,  the  current  directory  is
              searched  if  no  file is found in PATH.  If the sourcepath option to the shopt builtin command is turned off, the PATH is not
              searched.  If any arguments are supplied, they become the positional parameters when  filename  is  executed.   Otherwise  the
              positional  parameters  are  unchanged.  The return status is the status of the last command exited within the script (0 if no
              commands are executed), and false if filename is not found or cannot be read.