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EXCLAMATION-POINT (!) system command

 On systems which make it possible for a user program to pass a  command
 to the  operating system  for execution  and then  return to  the  user
 program, this command makes it possible to do so.  A typical use  might
 be to obtain a file directory listing because the user forgot the  name
 of a required input file.  This command is also available as the SYSTEM
 command, but this  short form  is convenient and  conventional on  Unix
 systems.
 
# Commentstring

 Comment line;  all  text  up to  the  next  comment marker  (#)  or  to
 end-of-line, whichever occurs  first, is ignored.   However, a  comment
 marker inside  a quoted  string,  or prefixed  by the  current  quoting
 character (see the EDIT command), is treated as an ordinary  character.
 The COMMENT ... ENDCOMMENT command  is useful for multi-line  comments.
 The comment marker character can be changed by the EDIT command.