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-- (more than 1 consecutive -)? e.g. ab--c
- at the back of words not allow, e.g. abc-
- at start of words not allow, e.g. -abc
^[A-Za-z0-9-]+$ is what I have so far.
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For examples, \+ matches "+" ; \[ matches "[" ; and \. matches "." . Regex also recognizes common escape sequences such as \n for newline, \t for tab, \r for carriage-return, \nnn for a up to 3-digit octal number, \xhh for a two-digit hex code, \uhhhh for a 4-digit Unicode, \uhhhhhhhh for a 8-digit Unicode.
Multiline option, or the m inline option, enables the regular expression engine to handle an input string that consists of multiple lines. It changes the interpretation of the ^ and $ language elements so that they match the beginning and end of a line, instead of the beginning and end of the input string.
You only need to escape the dash character if it could otherwise be interpreted as a range indicator (which can be the case inside a character class). Save this answer.
^(?!-)(?!.*--)[A-Za-z0-9-]+(?<!-)$
Explanation:
^ # Anchor at start of string
(?!-) # Assert that the first character isn't a -
(?!.*--) # Assert that there are no -- present anywhere
[A-Za-z0-9-]+ # Match one or more allowed characters
(?<!-) # Assert that the last one isn't a -
$ # Anchor at end of string
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