(PHP 4, PHP 5)
exec — Execute an external program
$command
[, array &$output
[, int &$return_var
]] )
exec() executes the given
command.
command
The command that will be executed.
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 \n, is not
included in this array. Note that if the array already contains some
elements, exec() will append to the end of the array.
If you do not want the function to append elements, call
unset() on the array before passing it to
exec().
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.
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() function.
To get the output of the executed command, be sure to set and use the
output parameter.
Example #1 An exec() 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');
?>
When allowing user-supplied data to be passed to this function, use escapeshellarg() or escapeshellcmd() to ensure that users cannot 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.
With safe mode enabled, the command string is escaped with escapeshellcmd(). Thus, echo y | echo x becomes echo y \| echo x.