There is no way to execute a command, feed it stuff on standard in, retrive the return code, standard out, and standard error.  exec() should probably have two additional arguments, an array for the output sent to standard error, and a string to be passed to to the child on standard in.

I could always pass arguments to commands, instead of having them read from standard in.  However, this is not a good idea from a security standpoint as argument values are visible to anybody on the system.

In my particular case, I've got a specialized, suid root, password change program I'd like to invoke from php.  This program takes a password on standard in.  If I don't give up and use perl, I'll probably use popen() and output redirection to guarenteed unique file names in /tmp to capture stdout and stderr, along with an echo of $? to get the return code.  In my case this will probably work.  In the general case writing to the file system could be a security problem. Certainlly it's a big hassle.