how to redirect php variable to stdin

Using popen()

For simple cases where you only need to write to the command's stdin (or only read from its stdout), popen() can be simpler.

php
$large_variable = "your large data string here...";
$command = "cat"; // Command to run. Open the process with write mode 'w' to send data to its stdin
$ph = popen($command, "w");
if ($ph) { fwrite($ph, $large_variable); pclose($ph); // Close the pipe
echo "Data sent to process.\n"; } else { echo "Error opening pipe.\n"; }