The Monastery mores hold that the poster of a question such as this should:

1. Show some effort: ie, post what you've tried
2. Tell how that code fails to meet your expectations (including error messages, if any)
3. Use the tools provided here (including Search and Super_Search, Tutorials, etc. to find answers before posting a question already answered repeatedly.

Hint: search terms such as "common strings" may be helpful.