( string command [, array output [, int return_var]])
exec() executes the given
command, however it does not output
anything. It simply returns 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.
If the output argument is present, then the
specified array will be filled with every line of output from the
command. Line endings, such as \n, are 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
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
例子 1. An exec() example
// outputs the username that owns the running php/httpd process
// (on a system with the "whoami" executable in the path)
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
注: 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".
See also system(),
escapeshellcmd(), and the backtick operator.