Get the path of ruby binary

gistfile1.diff

diff --git a/ext/etc/etc.c b/ext/etc/etc.c
index 2bd2e30..9da0ed7 100644
--- a/ext/etc/etc.c
+++ b/ext/etc/etc.c
@@ -597,6 +597,155 @@ etc_systmpdir(void)
     return tmpdir;
 }
 
+#ifdef _WIN32
+# define RUBYPATH_GetModuleFileName
+#elif defined(__APPLE__)
+# define RUBYPATH_NSGetExecutablePath
+# include <mach-o/dyld.h>
+#elif defined(__sun__)
+# define RUBYPATH_getexecname
+#elif defined(_AIX) || defined(__OpenBSD__)
+# define RUBYPATH_dladdr
+# include <dlfcn.h>
+#elif defined(__FreeBSD__)
+# define RUBYPATH_sysctl
+# include <sys/sysctl.h>
+# include <errno.h>
+#elif defined(__linux__) || defined(__NetBSD__) || defined(__DragonFly__)
+# define RUBYPATH_procfs
+#endif
+
+/*
+ * call-seq:
+ *     Etc.rubypath  ->  string
+ *
+ * Returns the real absolute path of current executing ruby.
+ * "real" means it doesn't include symlinks.
+ * If the environment doesn't support this, raises NotImplementedError.
+ *
+ * Example in shell:
+ *   % pwd
+ *   /hoge
+ *   % ls -l
+ *   lrwxr-xr-x  1 rubyist users      32 Jan  1 00:00 foo -> /usr/local/bin/ruby
+ *   % ./foo -retc -e'puts Etc.rubypath'
+ *   /usr/local/bin/ruby
+ *   % cd /
+ *   % PATH=/hoge foo -retc -e'puts Etc.rubypath'
+ *   /usr/local/bin/ruby
+ */
+static VALUE
+etc_rubypath(void)
+{
+#ifdef RUBYPATH_GetModuleFileName
+    char buf[4096];
+    size_t len;
+    len = (size_t)GetModuleFileName(NULL, buf, sizeof(buf));
+    if (len == 0) rb_sys_fail("Can't get the path of ruby");
+    return rb_filesystem_str_new(buf, len);
+#elif defined(RUBYPATH_NSGetExecutablePath)
+    /*
+     * defined(__APPLE__): returns absolute but symlink; need realpath
+     */
+    VALUE v;
+    uint32_t len = 0;
+    char *buf, *resolved
+    int err;
+    _NSGetExecutablePath(NULL, &len);
+    buf = malloc(len);
+    if (buf == NULL) rb_sys_fail("Can't allocate memory");
+    err = _NSGetExecutablePath(buf, &len);
+    if (err != 0) rb_sys_fail("Can't get the path of ruby");
+    resolved = realpath(buf, NULL);
+    if (resolved == NULL) rb_sys_fail("Can't get the path of ruby");
+    v = rb_filesystem_str_new_cstr(resolved);
+    free(buf);
+    free(resolved);
+    return v;
+#elif defined(RUBYPATH_getexecname)
+    const char *name = getexecname();
+    if (name == NULL) rb_sys_fail("Can't get the path of ruby");
+    return rb_filesystem_str_new_cstr(name);
+#elif defined(RUBYPATH_dladdr)
+    /*
+     * defined(__FreeBSD__): returns absolute but symlink; need realpath
+     * defined(__NetBSD__): returns relative; can't use
+     * defined(__OpenBSD__): returns relative; can't use
+     * defined(__DragonFly__): returns relative; can't use
+     * defined(__sun__):
+     * defined(_AIX):
+     * defined(__APPLE__): returns absolute but symlink; need realpath
+     *
+     * On relative platform, dln_find_exe can be used.
+     */
+    VALUE v;
+    char *resolved;
+    Dl_info info;
+    extern char **environ; /* environ should be in "ruby" not libruby */
+    if (dladdr(&environ, &info) == 0)
+	rb_sys_fail("Can't get the path of ruby");
+    resolved = realpath(info.dli_fname, NULL); /* realpath(, NULL) is platform dependent */
+    if (resolved == NULL) rb_sys_fail("Can't get the path of ruby");
+    v = rb_filesystem_str_new_cstr(resolved);
+    free(resolved);
+    return v;
+#elif defined(RUBYPATH_sysctl)
+    /*
+     * defined(__FreeBSD__): returns absolute
+     */
+    VALUE v;
+    int mib[4], err;
+    char *buf;
+    size_t len = 0;
+    mib[0] = CTL_KERN;
+    mib[1] = KERN_PROC;
+    mib[2] = KERN_PROC_PATHNAME;
+    mib[3] = -1;
+    err = sysctl(mib, 4, NULL, &len, NULL, 0);
+    if (err) rb_sys_fail("Can't get the path of ruby");
+    buf = malloc(len);
+    if (buf == NULL) rb_sys_fail("Can't allocate memory");
+    err = sysctl(mib, 4, buf, &len, NULL, 0);
+    if (err) {
+	free(buf);
+	rb_sys_fail("Can't get the path of ruby");
+    }
+    len--;
+    v = rb_filesystem_str_new(buf, len);
+    free(buf);
+    return v;
+#elif defined(RUBYPATH_procfs)
+    /*
+     * defined(__linux__): returns absolute
+     * defined(__NetBSD__): returns absolute
+     * defined(__DragonFly__): returns absolute
+     */
+    VALUE v;
+    size_t bufsiz = PATH_MAX;
+    char buf[PATH_MAX];
+    ssize_t len = 0;
+# if defined(__linux__) /* solaris 10+ */
+    len = readlink("/proc/self/exe", buf, bufsiz);
+# elif defined(__DragonFly__)
+    len = readlink("/proc/curproc/file", buf, bufsiz);
+# elif defined(__NetBSD__)
+    len = readlink("/proc/curproc/exe", buf, bufsiz);
+# else
+    rb_notimplement();
+# endif
+    if (len < 0) {
+	rb_sys_fail("Can't get the path of ruby");
+    }
+    /* assume PATH_MAX is enough length */
+    v = rb_filesystem_str_new(buf, len);
+    return v;
+#else
+    rb_notimplement();
+    return Qnil; /* dummy */
+#endif
+}
+
 /*
  * The etc module provides access to information from the running OS.
  *
@@ -625,6 +774,7 @@ Init_etc(void)
     rb_define_module_function(mEtc, "getgrent", etc_getgrent, 0);
     rb_define_module_function(mEtc, "sysconfdir", etc_sysconfdir, 0);
     rb_define_module_function(mEtc, "systmpdir", etc_systmpdir, 0);
+    rb_define_module_function(mEtc, "rubypath", etc_rubypath, 0);
 
     sPasswd =  rb_struct_define("Passwd",
 				"name", "passwd", "uid", "gid",

TODO:

• https://twitter.com/unak/status/445463345873686528
• http://stackoverflow.com/a/473150/515572