$re = '/0*([0-9]+)/';
$str = '29047531,000000029047531,70098877,000000000206616,TEST_MID_a8c59c12-5ffa-43dc-81f8-0ea4e9435a4d,000000000206616,TEST_MID_a8c59c12-5ffa-43dc-81f8-0ea4e9435a4d,TEST_MID_0ae1a070-7868-4543-811f-695f298cc9af,000000000206616,TEST_MID_a8c59c12-5ffa-43dc-81f8-0ea4e9435a4d,TEST_MID_0ae1a070-7868-4543-811f-695f298cc9af,TEST_MID_e189672a-9660-42a8-805b-b4e1f7fb431b,000000000206616,TEST_MID_a8c59c12-5ffa-43dc-81f8-0ea4e9435a4d,TEST_MID_0ae1a070-7868-4543-811f-695f298cc9af,TEST_MID_e189672a-9660-42a8-805b-b4e1f7fb431b,TEST_MID_75dc1b8b-7531';
$subst = "$1";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php