(PHP 4, PHP 5, PHP 7)
popen — Opens process file pointer
Opens a pipe to a process executed by forking the command given
Returns a file pointer identical to that returned by fopen(), except that it is unidirectional (may only be used for reading or writing) and must be closed with pclose(). This pointer may be used with fgets(), fgetss(), and fwrite(). When the mode is 'r', the returned file pointer equals to the STDOUT of the command, when the mode is 'w', the returned file pointer equals to the STDIN of the command.
If an error occurs, returns
Example #1 popen() example
$handle = popen("/bin/ls", "r");
If the command to be executed could not be found, a valid resource is returned. This may seem odd, but makes sense; it allows you to access any error message returned by the shell:
Example #2 popen() example
/* Add redirection so we can get stderr. */
$handle = popen('/path/to/executable 2>&1', 'r');
echo "'$handle'; " . gettype($handle) . "\n";
$read = fread($handle, 2096);
If you're looking for bi-directional support (two-way), use proc_open().