The passthru() function is
similar to the exec() function in that it executes a command. If the return_var argument is present, the
return status of the Unix command will be placed here. 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.
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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.
See also exec(), system(), popen(),
escapeshellcmd(), and the backtick
operator.