Regex to disallow more than 1 dash consecutively

Question

1. How can I disallow -- (more than 1 consecutive -)? e.g. ab--c
2. - at the back of words not allow, e.g. abc-<

Answer 1

^[a-zA-Z0-9](?!.*--)[a-zA-Z0-9-]*[a-zA-Z0-9]$

^[a-zA-Z0-9]     /*Starts with a letter or a number*/
(?!.*--)         /*Doesn't include 2 dashes in a row*/
[a-zA-Z0-9-]*    /*After first character, allow letters or numbers or dashes*/
[a-zA-Z0-9]$     /*Ends with a letter or a number*/

Matches:

Re-play / Re-play-ed

Doesn't Match:

Replay- / Re--Play / -Replay