system -- Execute an external program and display the output
string system ( string command [, int &return_var] )
system() is just like the C version of the
function in that it executes the given
command and outputs the result.
The system() call also tries to automatically
flush the web server's output buffer after each line of output if
PHP is running as a server module.
If you need to execute a command and have all the data from the
command passed directly back without any interference, use the
The command that will be executed.
If the return_var argument is present, then the
return status of the executed command will be written to this
Returns the last line of the command output on success, and FALSE
Example 1. system() example
<?php echo '<pre>';
// Outputs all the result of shellcommand "ls", and returns // the last output line into $last_line. Stores the return value // of the shell command in $retval. $last_line = system('ls', $retval);
// Printing additional info echo ' </pre> <hr />Last line of the output: ' . $last_line . ' <hr />Return value: ' . $retval; ?>
If you are going to allow data coming
from user input to be passed to this function, then you should be using
escapeshellarg() or escapeshellcmd()
to make sure that users cannot trick the system into executing arbitrary
Note: If you start a program using this function
and want to leave it running in the background, you have to make sure that the
output of that program is redirected to a file or some other output stream or
else PHP will hang until the execution of the program ends.
safe mode is enabled, you can only
execute executables 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,
all words following the initial command string are treated as a single argument. Thus,
echo y | echo x becomes echo "y | echo x".