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*************************** Motivation **********************************

Many interactive programs read input line by line, but would like to

provide line editing and history functionality to the end-user that

runs the program.

The input-edit package provides that functionality.  As far as the

programmer is concerned, the program only asks for the next line

of input. However, until the user presses the RETURN key they can use

emacs-style line editing commands and can traverse the history of lines

previously typed.

Other packages, such as GNU's readline, have greater capability but are

also substantially larger.  Input-edit is small, since it uses neither

stdio nor any termcap features, and is also quite portable.  It only uses

\b to backspace and \007 to ring the bell on errors.  Since it cannot

edit multiple lines it scrolls long lines left and right on the same line.

Input edit uses classic (not ANSI) C, and should run on any Unix

system (BSD, SYSV or POSIX), PC's under DOS with MSC, TurboC or djgpp,

PC's under OS/2 with gcc (EMX), or Vax/VMS.  Porting the package to new

systems basicaly requires code to read a character when it is typed without

echoing it, everything else should be OK.

I have run the package on:

        DECstation 5000, Ultrix 4.3 with cc 2.1 and gcc 2.3.3

        Sun Sparc 2, SunOS 4.1.1, with cc

        SGI Iris, IRIX System V.3, with cc

        PC using DOS with MSC

The description below is broken into two parts, the end-user (editing)

interface and the programmer interface.  Send bug reports, fixes and

enhancements to:

Chris Thewalt (thewalt@ce.berkeley.edu)

5/3/93

Thanks to the following people who have provided enhancements and fixes:

  Ron Ueberschaer, Christoph Keller, Scott Schwartz, Steven List,

  DaviD W. Sanderson, Goran Bostrom, Michael Gleason, Glenn Kasten,

  Edin Hodzic, Eric J Bivona, Kai Uwe Rommel, Danny Quah, Ulrich Betzler

PS: I don't have, and don't want to add, a vi mode, sorry.

************************** End-User Interface ***************************

Entering printable keys generally inserts new text into the buffer (unless

in overwrite mode, see below).  Other special keys can be used to modify

the text in the buffer.  In the description of the keys below, ^n means

Control-n, or holding the CONTROL key down while pressing "n".  Errors

will ring the terminal bell.

^A/^E   : Move cursor to beginning/end of the line.

^F/^B   : Move cursor forward/backward one character.

ESC-F   : Move cursor forward one word.

ESC-B   : Move cursor backward one word.

^D      : Delete the character under the cursor.

^H, DEL : Delete the character to the left of the cursor.

^K      : Kill from the cursor to the end of line.

^L      : Redraw current line.

^O      : Toggle overwrite/insert mode. Initially in insert mode. Text

          added in overwrite mode (including yanks) overwrite

          existing text, while insert mode does not overwrite.

^P/^N   : Move to previous/next item on history list.

^R/^S   : Perform incremental reverse/forward search for string on

          the history list.  Typing normal characters adds to the current

          search string and searches for a match. Typing ^R/^S marks

          the start of a new search, and moves on to the next match.

          Typing ^H or DEL deletes the last character from the search

          string, and searches from the starting location of the last search.

          Therefore, repeated DEL's appear to unwind to the match nearest

          the point at which the last ^R or ^S was typed.  If DEL is

          repeated until the search string is empty the search location

          begins from the start of the history list.  Typing ESC or

          any other editing character accepts the current match and

          loads it into the buffer, terminating the search.

^T      : Toggle the characters under and to the left of the cursor.

^U      : Deletes the entire line

^Y      : Yank previously killed text back at current location.  Note that

          this will overwrite or insert, depending on the current mode.

TAB     : By default adds spaces to buffer to get to next TAB stop

          (just after every 8th column), although this may be rebound by the

          programmer, as described below.

NL, CR  : returns current buffer to the program.

DOS and ANSI terminal arrow key sequences are recognized, and act like:

  up    : same as ^P

  down  : same as ^N

  left  : same as ^B

  right : same as ^F

************************** Programmer Interface ***************************

The programmer accesses input-edit through these functions, and optionally

through three additional function pointer hooks.  The four functions are:

char *gl_getline(char *prompt)

        Prints the prompt and allows the user to edit the current line. A

        pointer to the line is returned when the user finishes by

        typing a newline or a return.  Unlike GNU readline, the returned

        pointer points to a static buffer, so it should not be free'd, and

        the buffer contains the newline character.  The user enters an

        end-of-file by typing ^D on an empty line, in which case the

        first character of the returned buffer is '\0'.  Getline never

        returns a NULL pointer.  The getline functions sets terminal modes

        needed to make it work, and resets them before returning to the

        caller.  The getline function also looks for characters that would

        generate a signal, and resets the terminal modes before raising the

        signal condition.  If the signal handler returns to getline,

        the screen is automatically redrawn and editing can continue.

        Getline now requires both the input and output stream be connected

        to the terminal (not redirected) so the main program should check

        to make sure this is true.  If input or output have been redirected

        the main program should use buffered IO (stdio) rather than

        the slow 1 character read()s that getline uses.

void gl_setwidth(int width)

        Set the width of the terminal to the specified width. The default

        width is 80 characters, so this function need only be called if the

        width of the terminal is not 80.  Since horizontal scrolling is

        controlled by this parameter it is important to get it right.

void gl_histadd(char *buf)

        The gl_histadd function checks to see if the buf is not empty or

        whitespace, and also checks to make sure it is different than

        the last saved buffer to avoid repeats on the history list.

        If the buf is a new non-blank string a copy is made and saved on

        the history list, so the caller can re-use the specified buf.

void gl_strwidth(size_t (*func)())

        The gl_strwidth function allows the caller to supply a pointer to

        a prompt width calculation function (strlen by default). This

        allows the caller to embed escape sequences in the prompt and then

        tell getline how many screen spaces the prompt will take up.

The main loop in testgl.c, included in this directory, shows how the

input-edit package can be used:

extern char *gl_getline();

extern void  gl_histadd();

main()

{

    char *p;

    do {

        p = gl_getline("PROMPT>>>> ");

        gl_histadd(p);

        fputs(p, stdout);

    } while (*p != 0);

}

In order to allow the main program to have additional access to the buffer,

to implement things such as completion or auto-indent modes, three

function pointers can be bound to user functions to modify the buffer as

described below.  By default gl_in_hook and gl_out_hook are set to NULL,

and gl_tab_hook is bound to a function that inserts spaces until the next

logical tab stop is reached.  The user can reassign any of these pointers

to other functions.  Each of the functions bound to these hooks receives

the current buffer as the first argument, and must return the location of

the leftmost change made in the buffer.  If the buffer isn't modified the

functions should return -1.  When the hook function returns the screen is

updated to reflect any changes made by the user function.

int (*gl_in_hook)(char *buf)

        If gl_in_hook is non-NULL the function is called each time a new

        buffer is loaded. It is called when getline is entered, with an

        empty buffer, it is called each time a new buffer is loaded from

        the history with ^P or ^N, and it is called when an incremental

        search string is accepted (when the search is terminated). The

        buffer can be modified and will be redrawn upon return to getline().

int (*gl_out_hook)(char *buf)

        If gl_out_hook is non-NULL it is called when a line has been

        completed by the user entering a newline or return. The buffer

        handed to the hook does not yet have the newline appended. If the

        buffer is modified the screen is redrawn before getline returns the

        buffer to the caller.

int (*gl_tab_hook)(char *buf, int prompt_width, int *cursor_loc)

        If gl_tab_hook is non-NULL, it is called whenever a tab is typed.

        In addition to receiving the buffer, the current prompt width is

        given (needed to do tabbing right) and a pointer to the cursor

        offset is given, where a 0 offset means the first character in the

        line.  Not only does the cursor_loc tell the programmer where the

        TAB was received, but it can be reset so that the cursor will end

        up at the specified location after the screen is redrawn.