(PHP 4 >= 4.3.0, PHP 5)

proc_open Execute a command and open file pointers for input/output


resource proc_open ( string $cmd , array $descriptorspec , array &$pipes [, string $cwd [, array $env [, array $other_options ]]] )

proc_open() is similar to popen() but provides a much greater degree of control over the program execution.



The command to execute


An indexed array where the key represents the descriptor number and the value represents how PHP will pass that descriptor to the child process. 0 is stdin, 1 is stdout, while 2 is stderr.

Each element can be:

  • An array describing the pipe to pass to the process. The first element is the descriptor type and the second element is an option for the given type. Valid types are pipe (the second element is either r to pass the read end of the pipe to the process, or w to pass the write end) and file (the second element is a filename).
  • A stream resource representing a real file descriptor (e.g. opened file, a socket, STDIN).

The file descriptor numbers are not limited to 0, 1 and 2 - you may specify any valid file descriptor number and it will be passed to the child process. This allows your script to interoperate with other scripts that run as "co-processes". In particular, this is useful for passing passphrases to programs like PGP, GPG and openssl in a more secure manner. It is also useful for reading status information provided by those programs on auxiliary file descriptors.


Will be set to an indexed array of file pointers that correspond to PHP's end of any pipes that are created.


The initial working dir for the command. This must be an absolute directory path, or NULL if you want to use the default value (the working dir of the current PHP process)


An array with the environment variables for the command that will be run, or NULL to use the same environment as the current PHP process


Allows you to specify additional options. Currently supported options include:

  • suppress_errors (windows only): suppresses errors generated by this function when it's set to TRUE
  • bypass_shell (windows only): bypass cmd.exe shell when set to TRUE
  • context: stream context used when opening files (created with stream_context_create())

Return Values

Returns a resource representing the process, which should be freed using proc_close() when you are finished with it. On failure returns FALSE.


Version Description
5.2.1 Added the bypass_shell option to the other_options parameter.
5.0.0 Added the cwd, env and other_options parameters.


Example #1 A proc_open() example

= array(
=> array("pipe""r"),  // stdin is a pipe that the child will read from
=> array("pipe""w"),  // stdout is a pipe that the child will write to
=> array("file""/tmp/error-output.txt""a"// stderr is a file to write to

$cwd '/tmp';
$env = array('some_option' => 'aeiou');

$process proc_open('php'$descriptorspec$pipes$cwd$env);

if (
is_resource($process)) {
// $pipes now looks like this:
    // 0 => writeable handle connected to child stdin
    // 1 => readable handle connected to child stdout
    // Any error output will be appended to /tmp/error-output.txt

fwrite($pipes[0], '<?php print_r($_ENV); ?>');


// It is important that you close any pipes before calling
    // proc_close in order to avoid a deadlock
$return_value proc_close($process);

"command returned $return_value\n";

The above example will output something similar to:

    [some_option] => aeiou
    [PWD] => /tmp
    [SHLVL] => 1
    [_] => /usr/local/bin/php
command returned 0



Windows compatibility: Descriptors beyond 2 (stderr) are made available to the child process as inheritable handles, but since the Windows architecture does not associate file descriptor numbers with low-level handles, the child process does not (yet) have a means of accessing those handles. Stdin, stdout and stderr work as expected.


If you only need a uni-directional (one-way) process pipe, use popen() instead, as it is much easier to use.

See Also

  • popen() - Opens process file pointer
  • exec() - Execute an external program
  • system() - Execute an external program and display the output
  • passthru() - Execute an external program and display raw output
  • stream_select() - Runs the equivalent of the select() system call on the given arrays of streams with a timeout specified by tv_sec and tv_usec
  • The backtick operator