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/*

From: Jeff Solomon <jsolomon@stanford.edu>

Date: Fri,  9 Apr 1999 10:13:27 -0700 (PDT)

To: chet@po.cwru.edu

Subject: new readline example

Message-ID: <14094.12094.527305.199695@mrclean.Stanford.EDU>

Chet,

I've been using readline 4.0. Specifically, I've been using the perl

version Term::ReadLine::Gnu. It works great.

Anyway, I've been playing around the alternate interface and I wanted

to contribute a little C program, callback.c, to you that you could

use as an example of the alternate interface in the /examples

directory of the readline distribution.

My example shows how, using the alternate interface, you can

interactively change the prompt (which is very nice imo). Also, I

point out that you must roll your own terminal setting when using the

alternate interface because readline depreps (using your parlance) the

terminal while in the user callback. I try to demostrate what I mean

with an example. I've included the program below.

To compile, I just put the program in the examples directory and made

the appropriate changes to the EXECUTABLES and OBJECTS line and added

an additional target 'callback'.

I compiled on my Sun Solaris2.6 box using Sun's cc.

Let me know what you think.

Jeff

*/

#if defined (HAVE_CONFIG_H)

#include <config.h>

#endif

#include <stdio.h>

#include <sys/types.h>

#ifdef HAVE_UNISTD_H

#include <unistd.h>

#endif

#include <termios.h>    /* xxx - should make this more general */

#ifdef READLINE_LIBRARY

#  include "readline.h"

#else

#  include <readline/readline.h>

#endif

/* This little examples demonstrates the alternate interface to using readline.

 * In the alternate interface, the user maintains control over program flow and

 * only calls readline when STDIN is readable. Using the alternate interface,

 * you can do anything else while still using readline (like talking to a

 * network or another program) without blocking.

 *

 * Specifically, this program highlights two importants features of the

 * alternate interface. The first is the ability to interactively change the

 * prompt, which can't be done using the regular interface since rl_prompt is

 * read-only.

 *

 * The second feature really highlights a subtle point when using the alternate

 * interface. That is, readline will not alter the terminal when inside your

 * callback handler. So let's so, your callback executes a user command that

 * takes a non-trivial amount of time to complete (seconds). While your

 * executing the command, the user continues to type keystrokes and expects them

 * to be re-echoed on the new prompt when it returns. Unfortunately, the default

 * terminal configuration doesn't do this. After the prompt returns, the user

 * must hit one additional keystroke and then will see all of his previous

 * keystrokes. To illustrate this, compile and run this program. Type "sleep" at

 * the prompt and then type "bar" before the prompt returns (you have 3

 * seconds). Notice how "bar" is re-echoed on the prompt after the prompt

 * returns? This is what you expect to happen. Now comment out the 4 lines below

 * the line that says COMMENT LINE BELOW. Recompile and rerun the program and do

 * the same thing. When the prompt returns, you should not see "bar". Now type

 * "f", see how "barf" magically appears? This behavior is un-expected and not

 * desired.

 */

void process_line(char *line);

int  change_prompt(void);

char *get_prompt(void);

int prompt = 1;

char prompt_buf[40], line_buf[256];

tcflag_t old_lflag;

cc_t     old_vtime;

struct termios term;

int

main()

{

    fd_set fds;

    /* Adjust the terminal slightly before the handler is installed. Disable

     * canonical mode processing and set the input character time flag to be

     * non-blocking.

     */

    if( tcgetattr(STDIN_FILENO, &term) < 0 ) {

        perror("tcgetattr");

        exit(1);

    }

    old_lflag = term.c_lflag;

    old_vtime = term.c_cc[VTIME];

    term.c_lflag &= ~ICANON;

    term.c_cc[VTIME] = 1;

    /* COMMENT LINE BELOW - see above */

    if( tcsetattr(STDIN_FILENO, TCSANOW, &term) < 0 ) {

        perror("tcsetattr");

        exit(1);

    }

    rl_add_defun("change-prompt", change_prompt, CTRL('t'));

    rl_callback_handler_install(get_prompt(), process_line);

    while(1) {

      FD_ZERO(&fds);

      FD_SET(fileno(stdin), &fds);

      if( select(FD_SETSIZE, &fds, NULL, NULL, NULL) < 0) {

        perror("select");

        exit(1);

      }

      if( FD_ISSET(fileno(stdin), &fds) ) {

        rl_callback_read_char();

      }

    }

}

void

process_line(char *line)

{

  if( line == NULL ) {

    fprintf(stderr, "\n", line);

    /* reset the old terminal setting before exiting */

    term.c_lflag     = old_lflag;

    term.c_cc[VTIME] = old_vtime;

    if( tcsetattr(STDIN_FILENO, TCSANOW, &term) < 0 ) {

        perror("tcsetattr");

        exit(1);

    }

    exit(0);

  }

  if( strcmp(line, "sleep") == 0 ) {

    sleep(3);

  } else {

    fprintf(stderr, "|%s|\n", line);

  }

  free (line);

}

int

change_prompt(void)

{

  /* toggle the prompt variable */

  prompt = !prompt;

  /* save away the current contents of the line */

  strcpy(line_buf, rl_line_buffer);

  /* install a new handler which will change the prompt and erase the current line */

  rl_callback_handler_install(get_prompt(), process_line);

  /* insert the old text on the new line */

  rl_insert_text(line_buf);

  /* redraw the current line - this is an undocumented function. It invokes the

   * redraw-current-line command.

   */

  rl_refresh_line(0, 0);

}

char *

get_prompt(void)

{

  /* The prompts can even be different lengths! */

  sprintf(prompt_buf, "%s",

    prompt ? "Hit ctrl-t to toggle prompt> " : "Pretty cool huh?> ");

  return prompt_buf;

}