<?php

function processLinesGroup($linesGroup) {
    // do something with the group of input lines
}

function processInputLines($inputLines) {
    $linesGroup = array();
    $maxLines = 50;

    foreach ($inputLines as $line) {
        array_push($linesGroup, $line);

        // Process the group each time it's growing to N items
        if (count($linesGroup) === $maxLines) {
            processLinesGroup($linesGroup);
            $linesGroup = array();
        }
    }

    // Process the remaining items in the end
    if (!empty($linesGroup)) {
        processLinesGroup($linesGroup);
    }
}