rl.c - readline for crepl.sh

rl.c

/* shamelessly copied from:
 * https://stackoverflow.com/questions/34660459/changing-tab-completion-for-read-builtin-in-bash
 * And modified a bit
 * Compile it like
 *  gcc rl.c -lreadline -o rl
 * And copy the rl binary to the same directory as crepl.sh
 * */
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include <readline/readline.h>

static void version(const char* progname) {
  fprintf(stderr, "%s 0.1\n", progname);
}
static void usage(const char* progname) {
  fprintf(stderr, "Usage: %s [-fhv] [-p PROMPT] [-n PROGNAME] [COMPLETION...]\n", progname);
  fprintf(stderr,
          "Reads one line using readline, and prints it to stdout.\n"
          "Returns success if a line was read.\n"
          "  -p PROMPT    Output PROMPT before requesting input.\n"
          "  -H HISTFILE  File to save the history to.\n"
          "  -n PROGNAME  Set application name to PROGNAME for readline config file\n"
          "               (Default: %s).\n"
          "  -f           Use filename completion as well as specified completions.\n"
          "  -h           Print this help text and exit.\n"
          "  -v           Print version number and exit.\n"
          "  COMPLETION   word to add to the list of possible completions.\n",
          progname);
}

/* Readline really likes globals, so none of its hooks take a context parameter. */
static char** completions = NULL;
static char* generate_next_completion(const char* text, int state) {
  static int index = 0;
  if (state == 0) index = 0; /* reset index if we're starting */
  size_t textlen = strlen(text);
  while (completions[index++])
    if (strncmp(completions[index - 1], text, textlen) == 0)
      return strdup(completions[index - 1]);
  return NULL;
}

/* We use this if we will fall back to filename completion */
static char** generate_completions(const char* text, int start, int end) {
  return rl_completion_matches(text, generate_next_completion);
}

int main (int argc, char **argv) {
  const char* prompt = "";
  const char* progname = strrchr(argv[0], '/');
  progname = progname ? progname + 1 : argv[0];
  rl_readline_name = progname;

  bool use_file_completion = false;
  const char *histfile = NULL;

  for (;;) {
    int opt = getopt(argc, argv, "+fp:n:hH:v");
    switch (opt) {
      case -1:  break;
      case 'f': use_file_completion = true; continue;
      case 'p': prompt = optarg; continue;
      case 'H': histfile = optarg; continue;
      case 'n': rl_readline_name = optarg; continue;
      case 'h': usage(progname); return 0;
      case 'v': version(progname); return 0;
      default:  usage(progname); return 2;
    }
    break;
  }

  if (histfile) {
      using_history();
      read_history(histfile);
  }

  /* The default is stdout, which would interfere with capturing output. */
  rl_outstream = stderr;

  completions = argv + optind;
  rl_completion_entry_function = rl_filename_completion_function;
  if (*completions) {
    if (use_file_completion)
      rl_attempted_completion_function = generate_completions; 
    else
      rl_completion_entry_function = generate_next_completion;
  } else {
    /* No specified strings */ 
    if (!use_file_completion)
      rl_inhibit_completion = true; 
  }

  char* line = readline(prompt);

  if (line) {
    puts(line);
    add_history(line);
    free(line);
    if (histfile) write_history(histfile);
    return 0;
  } else {
    fputc('\n', rl_outstream);
    return 1;
  }
}