(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. No value
is returned. If a program is started with this function, in
order for it to continue running in the background, the output
of the program must be redirected to a file or another output
stream. Failing to do so will cause PHP to hang until the
execution of the program ends.