Proposal: getdirname utility

From: Damir Simunic <damir.simunic_at_gmail.com>
Date: Mon, 31 Mar 2025 18:43:19 +0200

Hi,


I’ve run into a curious problem while trying to package s6 supervision suite in a macOS .app bundle. As I’d like the bundle to work regardless of the folder it is in (not just in /Applications), I cannot set the PATH env variable in the bundle configuraiton (the plist file). Without an absolute PATH, s6-svscan cannot find s6-supervise.

Setting the bundle executable to `getcwd PATH s6-svscan` sadly also fails, as macOS launchd sets the process cwd to / and argv[0] to naked executable name, resulting in PATH being set to /.

So I modified getcwd into this getdirname utility that is supposed to use os-specific mechanisms to find its own path. This solved the problem, at least on a mac. Didn’t test on linux yet, though, and have no access to a BSD machine.

Wondering if this is of interest to propose as a patch to execline repo? I’m not experienced with skarnet coding style, any comments, pointers, reviews are most welcome.

Thanks,
Damir

p.s. IIUC one could achieve the same functionality by linking to `libld` to avoid per-platform conditional compilation; don’t know if that is more preferable.

The source, also attached as a file:

```
/* ISC license. */

#include <string.h>
#include <stdlib.h>

#ifdef __APPLE__
#include <mach-o/dyld.h>
#elif defined(__BSD__)
#include <sys/types.h>
#include <sys/sysctl.h>
#endif

#include <skalibs/sgetopt.h>
#include <skalibs/strerr.h>
#include <skalibs/stralloc.h>
#include <skalibs/djbunix.h>

#include <execline/execline.h>

#define USAGE "getdirname [ -E | -e ] variable prog..."
#define dieusage() strerr_dieusage(100, USAGE)


int sagetdirname(stralloc *sa) {

#ifdef __linux__
  return sareadlink(&sa, "/proc/self/exe");
#elif defined(__APPLE__)
{
  uint32_t size = 0;

  _NSGetExecutablePath(NULL, &size);
  if (!stralloc_ready(sa, size))
      strerr_diefu1sys(111, "stralloc_ready");

  if (_NSGetExecutablePath(sa->s, &size))
      strerr_diefu1sys(111, "_NSGetExecutablePath");

  sa->len = size;

  return 0;
}
#elif defined(__BSD__)
{
  int mib[4] = { CTL_KERN, KERN_PROC, KERN_PROC_PATHNAME, -1 };
  size_t size = 0;

  if (sysctl(mib, 4, NULL, &size, NULL, 0) == -1)
    strerr_diefu1sys(111, "sysctl get size");

  if (!stralloc_ready(sa, size))
    strerr_diefu1sys(111, "stralloc_ready");

  if (sysctl(mib, 4, sa->s, &size, NULL, 0) == -1)
    strerr_diefu1sys(111, "sysctl get path");

  sa->len = size;

  return 0;
}
#endif

  return -1;
}


int main (int argc, char const *const *argv)
{
  int doimport = 0 ;
  stralloc sa = STRALLOC_ZERO ;
  PROG = "getdirname" ;
  {
    subgetopt l = SUBGETOPT_ZERO ;
    for (;;)
    {
      int opt = subgetopt_r(argc, argv, "Ee", &l) ;
      if (opt == -1) break ;
      switch (opt)
      {
        case 'E' : doimport = 1 ; break ;
        case 'e' : doimport = 0 ; break ;
        default : dieusage() ;
      }
    }
    argc -= l.ind ; argv += l.ind ;
  }
  if (argc < 2) dieusage() ;
  if (!argv[0][0] || strchr(argv[0], '=')) strerr_dief1x(100, "invalid variable name") ;

  if (sagetdirname(&sa) < 0 || !stralloc_0(&sa)) strerr_diefu1sys(111, "getdirname") ;

  stralloc dirname = STRALLOC_ZERO ;

  if (!sadirname(&dirname, sa.s, sa.len))
    strerr_diefu2sys(111, "get dirname of ", sa.s) ;

  el_modif_and_exec(argv + 1, argv[0], dirname.s, doimport) ;
}
```


Received on Mon Mar 31 2025 - 18:43:19 CEST