Perl script reads line from stdin, writes response to stdout. It doesn't work when executed from php

test.php

<?php

$descriptors = [
    0 => ["pipe", "r"],  // stdin is a pipe that the child will read from
    1 => ["pipe", "w"],  // stdout is a pipe that the child will write to
    2 => ["pipe", "w"],   // stderr is a file to write to
];
$pipes = [];
$command = 'perl test.pl';
$process = proc_open($command, $descriptors, $pipes);

echo "writing to stdin\n";
fputs($pipes[0], "test\r\n");

echo "reading from stdout\n";
echo fgets($pipes[1]);

echo "done\n";

test.pl

while (my $line = <STDIN>) {
    print $line;
}