Linux

SHELL BUILTIN COMMANDS
     Unless otherwise noted, each builtin command  documented  in
     this  section  as accepting options preceded by - accepts --
     to signify the end of the options.
     : [arguments]
          No effect; the command does  nothing  beyond  expanding
          arguments and performing any specified redirections.  A
          zero exit code is returned.

      .  filename [arguments]
     source filename [arguments]
          Read and execute commands from filename in the  current
          shell  environment  and  return  the exit status of the
          last command executed from filename.  If filename  does
          not  contain  a  slash,  file names in PATH are used to
          find  the  directory  containing  filename.   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  exe-
          cuted.    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.