It seems to me that your program is doing exactly what you're telling it to. It reads a line of STDIN and prints it to STDOUT, then exits.

You might want to try something along these lines:

while (<STDIN>) {
    print STDOUT "The next line is: $_\n";
}
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A minor note, I think your select and exit are superfluous. For that matter, so is the STDOUT in print STDOUT.

Also, explore Apache's Conditional Logging capability.