What potential issue arises when using the stdin function in PHP scripts?

When using the stdin function in PHP scripts, one potential issue that can arise is that it may block the script execution if there is no input provided. To solve this issue, you can check if there is any input available before reading from stdin using the stream_select function.

$read = [STDIN];
$write = [];
$except = [];
if (stream_select($read, $write, $except, 0) === 1) {
    $input = fgets(STDIN);
    // Process the input here
} else {
    echo "No input provided.\n";
}