.nf
 NAME
     jucmd(3f)

 SYNOPSIS/USAGE
     jucmd(3f) from module M_history lets you add command line history editing
     to your program. To use it, read input lines into a character variable
     and then pass them to the routine. The returned string can then be parsed
     or read from with an internal READ. So if you have an existing READ

        READ(5,101)A,I,K

     replace it with something like

        USE M_HISTORY,ONLY : JUCMD  
        CHARACTER(LEN=255) :: LINE

        READ(5,'(A)') LINE
	CALL JUCMD(LINE)
        READ(LINE,101)A,I,K

     Then if anyone enters "r" on a line by itself or a line beginning with "r ",
     the user will enter the command history editing mode.

 DESCRIPTION

     Usage from programs calling jucmd(3f):
        r              # enter command history editing mode
        r [directive]  # recall and display or edit previously entered commands

     Enter an R command on a line by itself to enter redo mode.
 
     The last command entered is displayed, preceded by an !.
 
     The character you respond with in column 1 controls what happens next.
 
      1. Use a positioning directive (/,l,u,d,N) to find the command to start
         editing if it was not the last command entered.
      2. Next enter an editing directive (c,m) as described below.
      3. Once the change is executed you will be prompted for another edit
         directive
      4. Once done editing (or listing) enter:
           ☆ a blank line (to execute the displayed command)
           ☆ a period (.) on a line by itself (which means cancel).
 
     N stands for a number in the following directives.
 
     LISTING COMMAND HISTORY (buffer set to last line displayed)
      l|p N      # list from line N. -N shows N last lines
      L|P N      # same as 'l' except no line numbers (for pasting)
      /string    # search for simple string in all history lines
 
     POSITIONING TO PREVIOUS COMMANDS
      u N        # up through buffer
      d N        # down through buffer
      N          # load line number
 
     EDITING THE CURRENT BUFFER LINE (Changing and Modifying)
      c/oldstring/newstring/  # change string
      s (for substitute) is a synonym for c.
 
      mmod_string
 
       If the first character of your entry is m or blank,
         REPLACE a string by entering a replacement character under it
         LEAVE a character alone by leaving a space under it
         DELETE a character by putting a # character under it
         BLANK OUT a character by putting an & under it
         INSERT A STRING by entering ^STRING#

     HELP
      h|?  # display help text
 
     DUMPING THE COMMAND HISTORY
      w FILENAME  # write entire command history to specified file
 
 EXAMPLE
 
     r
     !math c(1)*sin(c(1))      # last command is displayed
     c/sin/cos/                # change a substring
     !math c(1)*cos(c(1))
                    ^1+#       # insert a string
     !math c(1)*cos(1+c(1))
             2             ))  # replace characters
     !math c(2)*cos(1+c(1))))
                           ##  # delete characters
     !math c(2)*cos(1+c(1))
         && &                  # replace characters with spaces
     !mat c 2)*cos(1+c(1))
     .                         # stop
 
 NOTES
     For the "c" directive the second character becomes the delimiter. Only use
     a delimiter of / or % or @. In the future other characters may not work.
 
     The "modify" directive takes a little practice if you were never a CDC NOS
     user but this single directive accommodates positionally deleting,
     replacing, and inserting text. In this implementation it is hard to put the
     strings "&" and "#" into your new commands. to put a # character into a
     string put something else there and change it to a # using the 'c' command.
     To put an & into a string use the same method or insert it using ^&#.

     As written, this module uses Fortran unit 71.