2 From: Jeff Solomon <jsolomon@stanford.edu>
3 Date: Fri, 9 Apr 1999 10:13:27 -0700 (PDT)
5 Subject: new readline example
6 Message-ID: <14094.12094.527305.199695@mrclean.Stanford.EDU>
10 I've been using readline 4.0. Specifically, I've been using the perl
11 version Term::ReadLine::Gnu. It works great.
13 Anyway, I've been playing around the alternate interface and I wanted
14 to contribute a little C program, callback.c, to you that you could
15 use as an example of the alternate interface in the /examples
16 directory of the readline distribution.
18 My example shows how, using the alternate interface, you can
19 interactively change the prompt (which is very nice imo). Also, I
20 point out that you must roll your own terminal setting when using the
21 alternate interface because readline depreps (using your parlance) the
22 terminal while in the user callback. I try to demostrate what I mean
23 with an example. I've included the program below.
25 To compile, I just put the program in the examples directory and made
26 the appropriate changes to the EXECUTABLES and OBJECTS line and added
27 an additional target 'callback'.
29 I compiled on my Sun Solaris2.6 box using Sun's cc.
31 Let me know what you think.
36 Copyright (C) 1999 Jeff Solomon
39 #if defined (HAVE_CONFIG_H)
44 #include <sys/types.h>
50 #include <termios.h> /* xxx - should make this more general */
52 #ifdef READLINE_LIBRARY
53 # include "readline.h"
55 # include <readline/readline.h>
58 /* This little examples demonstrates the alternate interface to using readline.
59 * In the alternate interface, the user maintains control over program flow and
60 * only calls readline when STDIN is readable. Using the alternate interface,
61 * you can do anything else while still using readline (like talking to a
62 * network or another program) without blocking.
64 * Specifically, this program highlights two importants features of the
65 * alternate interface. The first is the ability to interactively change the
66 * prompt, which can't be done using the regular interface since rl_prompt is
69 * The second feature really highlights a subtle point when using the alternate
70 * interface. That is, readline will not alter the terminal when inside your
71 * callback handler. So let's so, your callback executes a user command that
72 * takes a non-trivial amount of time to complete (seconds). While your
73 * executing the command, the user continues to type keystrokes and expects them
74 * to be re-echoed on the new prompt when it returns. Unfortunately, the default
75 * terminal configuration doesn't do this. After the prompt returns, the user
76 * must hit one additional keystroke and then will see all of his previous
77 * keystrokes. To illustrate this, compile and run this program. Type "sleep" at
78 * the prompt and then type "bar" before the prompt returns (you have 3
79 * seconds). Notice how "bar" is re-echoed on the prompt after the prompt
80 * returns? This is what you expect to happen. Now comment out the 4 lines below
81 * the line that says COMMENT LINE BELOW. Recompile and rerun the program and do
82 * the same thing. When the prompt returns, you should not see "bar". Now type
83 * "f", see how "barf" magically appears? This behavior is un-expected and not
87 void process_line(char *line
);
88 int change_prompt(void);
89 char *get_prompt(void);
92 char prompt_buf
[40], line_buf
[256];
102 /* Adjust the terminal slightly before the handler is installed. Disable
103 * canonical mode processing and set the input character time flag to be
106 if( tcgetattr(STDIN_FILENO
, &term
) < 0 ) {
110 old_lflag
= term
.c_lflag
;
111 old_vtime
= term
.c_cc
[VTIME
];
112 term
.c_lflag
&= ~ICANON
;
113 term
.c_cc
[VTIME
] = 1;
114 /* COMMENT LINE BELOW - see above */
115 if( tcsetattr(STDIN_FILENO
, TCSANOW
, &term
) < 0 ) {
120 rl_add_defun("change-prompt", change_prompt
, CTRL('t'));
121 rl_callback_handler_install(get_prompt(), process_line
);
125 FD_SET(fileno(stdin
), &fds
);
127 if( select(FD_SETSIZE
, &fds
, NULL
, NULL
, NULL
) < 0) {
132 if( FD_ISSET(fileno(stdin
), &fds
) ) {
133 rl_callback_read_char();
139 process_line(char *line
)
142 fprintf(stderr
, "\n", line
);
144 /* reset the old terminal setting before exiting */
145 term
.c_lflag
= old_lflag
;
146 term
.c_cc
[VTIME
] = old_vtime
;
147 if( tcsetattr(STDIN_FILENO
, TCSANOW
, &term
) < 0 ) {
154 if( strcmp(line
, "sleep") == 0 ) {
157 fprintf(stderr
, "|%s|\n", line
);
166 /* toggle the prompt variable */
169 /* save away the current contents of the line */
170 strcpy(line_buf
, rl_line_buffer
);
172 /* install a new handler which will change the prompt and erase the current line */
173 rl_callback_handler_install(get_prompt(), process_line
);
175 /* insert the old text on the new line */
176 rl_insert_text(line_buf
);
178 /* redraw the current line - this is an undocumented function. It invokes the
179 * redraw-current-line command.
181 rl_refresh_line(0, 0);
187 /* The prompts can even be different lengths! */
188 sprintf(prompt_buf
, "%s",
189 prompt
? "Hit ctrl-t to toggle prompt> " : "Pretty cool huh?> ");
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