(PHP 4, PHP 5)
passthru — Execute an external program and display raw output
The passthru() function is similar to the exec() function in that it executes a command . This function should be used in place of exec() or system() when the output from the Unix command is binary data which needs to be passed directly back to the browser. A common use for this is to execute something like the pbmplus utilities that can output an image stream directly. By setting the Content-type to image/gif and then calling a pbmplus program to output a gif, you can create PHP scripts that output images directly.
The command that will be executed.
If the return_var argument is present, the return status of the Unix command will be placed here.
Note: 如果用本函数启动一个程序并希望保持在后台运行，必须确保该程序的输出被重定向到一个文件或者其它输出流去，否则 PHP 会在程序执行结束前挂起。