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# CXVII. POSIX Functions

# Introduction

This module contains an interface to those functions defined in the IEEE 1003.1 (POSIX.1) standards document which are not accessible through other means. POSIX.1 for example defined the open(), read(), write() and close() functions, too, which traditionally have been part of PHP 3 for a long time. Some more system specific functions have not been available before, though, and this module tries to remedy this by providing easy access to these functions.

Warning
Sensitive data can be retrieved with the POSIX functions, e.g. posix_getpwnam() and friends. None of the POSIX function perform any kind of access checking when safe mode is enabled. It's therefore strongly advised to disable the POSIX extension at all (use --disable-posix in your configure line) if you're operating in such an environment.

> Note: This extension is not available on Windows platforms.

# Installation

POSIX functions are enabled by default. You can disable POSIX-like functions with --disable-posix.

# Predefined Constants

The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.

`POSIX_F_OK` (integer)

  Check whether the file exists.

`POSIX_R_OK` (integer)

  Check whether the file exists and has read permissions.

`POSIX_W_OK` (integer)

  Check whether the file exists and has write permissions.

`POSIX_X_OK` (integer)

  Check whether the file exists and has execute permissions.

`POSIX_S_IFBLK` (integer)

  Block special file

`POSIX_S_IFCHR` (integer)

  Character special file

`POSIX_S_IFIFO` (integer)

  FIFO (named pipe) special file

`POSIX_S_IFREG` (integer)

  Normal file

`POSIX_S_IFSOCK` (integer)

  Socket

> Note: These constants are available since PHP 5.1.0. Please also note that some of them may not be available in your system.

# See Also

The section about Process Control Functions maybe of interest for you.

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