php exec函数不能执行...急..............

。。。你看exec的函数返回值是什么！！！
exec等只会有返回值，而不会弹出窗口。you know?
你可以指定输出和返回值的，看看手册吧。。它有三个参数呢
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.

返回值
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.