Using readline's rl_insert_text on OS X 10.5

Question

So, I'm trying to stuff some default text into a user input using readline, and having trouble getting it to work on OSX 10.5:

// rl_insert_text_ex.c
// gcc -o rl_insert_text_ex rl_insert_text_ex.c -lreadline
#include <stdio.h>
#include <readline/readline.h>

int my_startup_hook(void) {
  return rl_insert_text("ponycorns");
}
int main(int argc, char *argv[]) {
  char *line;
  rl_startup_hook = (Function*) my_startup_hook;
  line = readline("What's your favorite mythical animal? ");
  if (NULL == line || '\0' == *line) {
    printf("Nothing given... :(\n");
  }
  else {
    printf("That's funny, I love %s too!\n", line);
  }
  return 0;
}

This code doesn't even compile on 10.4 (no definition for _rl_insert_text on 10.4, which is a bit of a bummer), but does compile on 10.5. However, the rl_insert_text()'d text is never shown to screen, nor returned as user input. The callback is being used and rl_insert_text() returns the proper value, (thank you, printf), so I'm not sure what's going on here.

I checked /usr/include/readline/readline.h, and rl_insert_text() is under:

/* supported functions */

which is confusingly under:

/*
 * The following is not implemented
 */

So am I SOL, or am I just doing it wrong?

Answer 1

Unfortunately, you may be out of luck, at least with the readline library included in OS X. Due to license compatibility issues, Apple uses libedit, which (apparently) provides incomplete readline emulation. (This library is documented with the name "editline" in the readline.h included with OS X.)

GNU Readline Library (the "one true" readline library) is under GPL, which (being a copyleft license) does not play well with code that is not entirely open-source. If it comes down to (A) open-sourcing all of Xcode, OS X, etc. or (B) using a knock-off of what you're really like to use, Apple (like most companies) is always going to choose B. It's a bummer, but that's life.

Personally, I think this is one reason that GPL'd code is somewhat of a blight on the land, since in the act of "sticking it to the man", it often also withholds the code from the masses who purchase software. The {BSD,MIT,Apache}-style licenses are much more conducive to use in closed-source systems, and still allow commercial entities to contribute back patches, etc. My guess is that libedit hasn't received enough attention to be fixed properly. Community patches would certainly be welcome, although it's so much nicer if we can use code without having to hack on it ourselves... ;-)

BTW, the same thing applies to other GPL projects — as long as {git,mercurial,bazaar} remains under GPL, don't hold your breath for Apple to ship integration for them in Xcode. :-(

UPDATE: The new Xcode 4 offers git support. Huzzah! My understanding is that this is due to the new plugin architecture which isolates GPL'd code from the main Xcode codebase. However, I emphasize that copyleft licenses are still the wrong solution for code that should benefit everyone. Obviously some people don't agree (you're a pal, anonymous downvoter) but the fact is that GPL can restrict freedoms too — usually its different ones than closed-source/proprietary software generally does, but GPL is also quite effective at preventing illegal use of source code... The difference is a feeling of moral superiority.