php grepでファイルの文字列取得

file_grep.php

<?php
echo "aaa";
echo PHP_EOL;
$cmd = 'find . -type f -name "*.txt" | xargs fgrep "Aki_Komo"';
$grep = exec($cmd);
$grep = preg_replace('/[^0-9]/', '', $grep);
echo $grep;
echo PHP_EOL;
?>