$re = '/^(.*):(.*):(.*):(.*):(.*):(.*):(.*):(.*)$/m';
$str = 'I have the following text document:
word1: word2: word3: word4: word5: word6: word7: word8 word9
word1: word2: word3: word4: word5: word6: word7: word8 word9
word1: word2: word3: word4: word5: word6: word7: word8 word9';
$subst = "$1,$2,$3,$4,$5,$6,$7,$8";
$result = preg_replace($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