How can I make regular expression for username that only starts with alphabet?

Ansh Ansh 0
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I'm trying to create a regular expression that will allow only specific usernames

  • Only starts with alphabet.
  • Only ends with either number or an alphabet.
  • Only allowed - if contains alphabets only or only one dot with alphabets, only one underscore with alphabets.
  • Cannot starts with dot or underscore
  • Length of username should be only in 4 to 10 char

this is what i am doing - ^(?=[a-zA-Z0-9._]{4,10}$)(?!.*[_.]{2})[^_.].*[^_.]$

regex
2 Answers

This should work for you:

^(?=[a-zA-Z0-9._]{4,10})[a-zA-Z](?:[a-zA-Z]+_[a-zA-Z0-9]+|[a-zA-Z]+\.[a-zA-Z0-9]+|[a-zA-Z0-9]+)$
Acuriousmind0

If the only problem currently is that it should not start with numbers, you could use one of these patterns that start the match with a char [A-Za-z] and ends the match with [a-zA-Z0-9]

In the middle there can only be 1 occurrence of either . or _

^(?=[a-zA-Z0-9._]{4,10}$)(?!.*[_.]{2})[A-Za-z]+(?:[_.][a-zA-Z0-9]+)?$

Regex demo

Or another variation:

^[a-zA-Z](?=[a-zA-Z0-9._]{3,9}$)[a-zA-Z0-9]*(?:[._][a-zA-Z0-9]*)?[a-zA-Z0-9]$

Regex demo

The fourth bird0
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