$re = '/(?:\d+[a-z]|[a-z]+\d)[a-z\d]*/m';
$str = 'asdasdas7
7sdfdf
a1
1a
0001a
0000a0000
a-1
1-a
a
1
eee
21123124
aaaa-111
1 a 6858 ghg 8768-zzt zz zt t-3
1212231234_sdfs1111dfsdf_ewrwerfwe_sef3325345';
$subst = "";
$result = preg_replace($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