php man page for exec

EXEC(3) 								 1								   EXEC(3)

exec - Execute an external program

SYNOPSIS
       string exec (string  $command, [array  &$output], [int  &$return_var])

DESCRIPTION
       exec(3) executes the given $command.

PARAMETERS
	      o $command
		- The command that will be executed.

	      o $output
		- If the $output argument is present, then the specified array will be filled with every line of output from the command. Trailing
		whitespace, such as 
, is not included in this array. Note that if the array already contains some elements, exec(3) will  append
		to  the  end  of  the  array.  If you do not want the function to append elements, call unset(3) on the array before passing it to
		exec(3).

	      o $return_var
		- If the $return_var argument is present along with the $output argument, then the return status of the executed command  will	be
		written to this variable.

RETURN VALUES
	The last line from the result of the command. If you need to execute a command and have all the data from the command passed directly back
       without any interference, use the passthru(3) function.

	To get the output of the executed command, be sure to set and use the $output parameter.

EXAMPLES
       Example #1

	      An exec(3) example

	      <?php
	      // outputs the username that owns the running php/httpd process
	      // (on a system with the "whoami" executable in the path)
	      echo exec('whoami');
	      ?>

NOTES
       Warning

	      When allowing user-supplied data to be passed to this function, use escapeshellarg(3) or escapeshellcmd(3) to ensure that users can-
	      not trick the system into executing arbitrary commands.

       Note

	      If a program is started with this function, in order for it to continue running in the background, the output of the program must be
	      redirected to a file or another output stream. Failing to do so will cause PHP to hang until the execution of the program ends.

       Note

	      When safe mode is enabled, you can only execute files within the safe_mode_exec_dir. For practical  reasons,  it	is  currently  not
	      allowed to have .. components in the path to the executable.

       Warning

	      With safe mode enabled, the command string is escaped with escapeshellcmd(3). Thus, echo y | echo x becomes echo y | echo x.

SEE ALSO
       system(3), passthru(3), escapeshellcmd(3), pcntl_exec(3), backtick operator.

PHP Documentation Group 														   EXEC(3)