source: vendor/bash/3.1-p17/examples/loadables/cat.c

/*
 * cat replacement
 *
 * no options - the way cat was intended
 */

#include <fcntl.h>
#include <errno.h>

#include "builtins.h"
#include "shell.h"

#ifndef errno
extern int errno;
#endif

extern char *strerror ();
extern char **make_builtin_argv ();

static int
fcopy(fd)
int     fd;
{
        char    buf[1024], *s;
        int     n, w, e;

        while (n = read(fd, buf, sizeof (buf))) {
                w = write(1, buf, n);
                if (w != n) {
                        e = errno;
                        write(2, "cat: write error: ", 18);
                        s = strerror(e);
                        write(2, s, strlen(s));
                        write(2, "\n", 1);
                        return 1;
                }
        }
        return 0;
}

cat_main (argc, argv)
int     argc;
char    **argv;
{
        int     i, fd, r;
        char    *s;

        if (argc == 1)
                return (fcopy(0));

        for (i = r = 1; i < argc; i++) {
                if (argv[i][0] == '-' && argv[i][1] == '\0')
                        fd = 0;
                else {
                        fd = open(argv[i], O_RDONLY, 0666);
                        if (fd < 0) {
                                s = strerror(errno);
                                write(2, "cat: cannot open ", 17);
                                write(2, argv[i], strlen(argv[i]));
                                write(2, ": ", 2);
                                write(2, s, strlen(s));
                                write(2, "\n", 1);
                                continue;
                        }
                }
                r = fcopy(fd);
                if (fd != 0)
                        close(fd);
        }
        return (r);
}

cat_builtin(list)
WORD_LIST *list;
{
        char    **v;
        int     c, r;

        v = make_builtin_argv(list, &c);
        r = cat_main(c, v);
        free(v);

        return r;
}

char *cat_doc[] = {
        "Read each FILE and display it on the standard output.   If any",
        "FILE is `-' or if no FILE argument is given, the standard input",
        "is read.",
        (char *)0
};

struct builtin cat_struct = {
        "cat",
        cat_builtin,
        BUILTIN_ENABLED,
        cat_doc,
        "cat [-] [file ...]",
        0
};