Resolve a symlink step by step, printing each link in the chain

lsln.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>

static char *getlink(const char *);
static void panic(const char *);

int
main(int argc, char **argv)
{
    if (getopt(argc, argv, "") != -1 || optind + 1 != argc) {
        fputs("usage: lsln [file]\n", stderr);
        exit(2);
    }

    const char *name = argv[optind];

    for (char *link, *path = getlink(name); path; link = getlink(path), free(path), path = link) {
        puts(path);
    }
}

char *
getlink(const char *path)
{
    struct stat st;

    if (lstat(path, &st) == -1)
        panic(path);

    if (!S_ISLNK(st.st_mode))
        return NULL;

    size_t size = st.st_size + 1;

    const char *ptr = strrchr(path, '/');
    size_t off = ptr ? ptr + 1 - path : 0;

    char *buf = malloc(size + off);

    if (!buf)
        panic(path);

    ssize_t len = readlink(path, buf, size);

    if (len == -1)
        panic(path);

    if (len == size)
        return NULL;

    buf[len++] = '\0';

    if (buf[0] != '/' && off != 0) {
        memmove(buf + off, buf, len);
        memcpy(buf, path, off);
    }

    return buf;
}

void
panic(const char *mesg)
{
    perror(mesg);
    exit(1);
}