说明
void
passthru ( string command [, int &return_var] )
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.
exec