environmental-sensor-uart/expirements/dio-test-read.php

<?php

$fd = dio_open("/dev/ttyACM0", O_RDWR | O_NONBLOCK | O_NOCTTY);

// first read  after initial power up:
$first = dio_read($fd, 1024);

// send an 'R', then read again
dio_write($fd, "R" . PHP_EOL);
sleep(1);
$second = dio_read($fd, 1024);

dio_close($fd);

var_dump(strlen($first), $first, PHP_EOL, "hello", strlen($second), $second);