Getting bash's pwd isn't possible where bash isn't used. What's your point? Are you implying that the code I posted isn't portable? If so, you'd be mistaken.

Update:

Every tool that gives you bash's pwd use $ENV{PWD}.

$ /bin/pwd              GNU pwd
/tmp/ikegami

$ bash -c pwd           bash's builtin
/home/ikegami/tmp

$ PWD=/ bash -c pwd     bash's builtin uses $ENV{PWD}
/tmp/ikegami
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The GNU pwd doesn't have any command line options and always gives the path returned by getcwd (with a fallback on error). Darwin's pwd goes a step further and does something that looks awfully familiar.

static char *
getcwd_logical(void)
{
    struct stat lg, phy;
    char *pwd;

    /*
     * Check that $PWD is an absolute logical pathname referring to
     * the current working directory.
     */
    if ((pwd = getenv("PWD")) != NULL && *pwd == '/') {
        if (stat(pwd, &lg) == -1 || stat(".", &phy) == -1)
            return (NULL);
        if (lg.st_dev == phy.st_dev && lg.st_ino == phy.st_ino)
            return (pwd);
    }

    errno = ENOENT;
    return (NULL);
}
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