chdir

/*
 *  call-seq:
 *     Dir.chdir( [ string] ) => 0
 *     Dir.chdir( [ string] ) {| path | block }  => anObject
 *
 *  Changes the current working directory of the process to the given
 *  string. When called without an argument, changes the directory to
 *  the value of the environment variable <code>HOME</code>, or
 *  <code>LOGDIR</code>. <code>SystemCallError</code> (probably
 *  <code>Errno::ENOENT</code>) if the target directory does not exist.
 *
 *  If a block is given, it is passed the name of the new current
 *  directory, and the block is executed with that as the current
 *  directory. The original working directory is restored when the block
 *  exits. The return value of <code>chdir</code> is the value of the
 *  block. <code>chdir</code> blocks can be nested, but in a
 *  multi-threaded program an error will be raised if a thread attempts
 *  to open a <code>chdir</code> block while another thread has one
 *  open.
 *
 *     Dir.chdir("/var/spool/mail")
 *     puts Dir.pwd
 *     Dir.chdir("/tmp") do
 *       puts Dir.pwd
 *       Dir.chdir("/usr") do
 *         puts Dir.pwd
 *       end
 *       puts Dir.pwd
 *     end
 *     puts Dir.pwd
 *
 *  <em>produces:</em>
 *
 *     /var/spool/mail
 *     /tmp
 *     /usr
 *     /tmp
 *     /var/spool/mail
 */
static VALUE
dir_s_chdir(argc, argv, obj)
    int argc;
    VALUE *argv;
    VALUE obj;
{
    VALUE path = Qnil;

    rb_secure(2);
    if (rb_scan_args(argc, argv, "01", &path) == 1) {
        SafeStringValue(path);
    }
    else {
        const char *dist = getenv("HOME");
        if (!dist) {
            dist = getenv("LOGDIR");
            if (!dist) rb_raise(rb_eArgError, "HOME/LOGDIR not set");
        }
        path = rb_str_new2(dist);
    }

    if (chdir_blocking > 0) {
        if (!rb_block_given_p() || rb_thread_current() != chdir_thread)
            rb_warn("conflicting chdir during another chdir block");
    }

    if (rb_block_given_p()) {
        struct chdir_data args;
        char *cwd = my_getcwd();

        args.old_path = rb_tainted_str_new2(cwd); free(cwd);
        args.new_path = path;
        args.done = Qfalse;
        return rb_ensure(chdir_yield, (VALUE)&args, chdir_restore, (VALUE)&args);
    }
    dir_chdir(path);

    return INT2FIX(0);
}