I have sample regex for check user nickname:
^[a-z][a-z0-9_](?:[a-z0-9]+)*$
This regex match correct nicknames:
But can't match like this correct nicknames:
In generaly how rewrite my regex for regx which can ignore sample wrong user names:
User nickname string on start can contain only a-z letters and in the middle (center) of string can contain a-z0-9_ and on the end can contain only a-z0-9
You may use
^[a-z](?:[a-z0-9_]*[a-z0-9])?$
See the regex demo.
Details
^ - start of string[a-z] - a lowercase ASCII letter(?:[a-z0-9_]*[a-z0-9])? - an optional sequence (it will make possible to match 1-char input) of[a-z0-9_]* - 0+ lowercase letters, digits or _[a-z0-9] - a lowercase ASCII letter or digit$ - end of stringIf there is a limit to the minimum chars in the input more than 1, you may remove the optional capturing group parentheses/quantifier and use
^[a-z][a-z0-9_]*[a-z0-9]$
And vice versa, to also allow an empty string, wrap with another optional group:
^(?:[a-z](?:[a-z0-9_]*[a-z0-9])?)?$
^^^ ^^
There may be other ways to write the pattern, e.g.
^(?=[a-z])[a-z0-9_]*$(?<=[a-z0-9])
that will match a string consisting of lowercase letters, digits or _ where the first char must be a lowercase letter and the last one should be either a letter or a digit.
See this regex demo.