What's the Absolute Path to a File?

There's no standard command that gives you the absolute path to a file. That's insane. Here's an implementation.

Yes, it resolves symlinks and works on directories, too.

I couldn't figure out how to get Blogger to stop re-formatting my code, so I passed it through this, web-based, C#-formatting tool (!), and now it seems to look okay.

Argh.

// realpath - what's the real path to a file?
// Turn relative paths into absolute paths,
//   resolve '.' and '..',
//   follow symlinks

#include <errno.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
  char path[_POSIX_PATH_MAX];

  if (argc != 2) {
    fprintf(stderr, "usage: %s filename\n", argv[0]);
    exit(EINVAL);
  }

  if (!realpath(argv[1], path)) {
    perror(NULL);
    exit(errno);
  }

  printf("%s\n", path);
  return(0);
}