From the GNU getcwd(3) manpage, paraphrased: returns the absolute pathname of the current working directory.  Fails when the current directory is not eradable.  Complies with POSIX.1 spec.(PHP 4, PHP 5, PHP 7, PHP 8)
posix_getcwd — Pathname of current directory
Gets the absolute pathname of the script's current working directory. On error, it sets errno which can be checked using posix_get_last_error()
此函数没有参数。
   Returns a string of the absolute pathname on success.  
   On error, returns false and sets errno which can be checked with
   posix_get_last_error().
  
示例 #1 posix_getcwd() example
This example will return the absolute path of the current working directory of the script.
<?php
echo 'My current working directory is '.posix_getcwd();
?>注意:
This function can fail on
- Read or Search permission was denied
- Pathname no longer exists
From the GNU getcwd(3) manpage, paraphrased: returns the absolute pathname of the current working directory.  Fails when the current directory is not eradable.  Complies with POSIX.1 spec.