regex for username validation php

Question

I am trying to make username validation with regex and PHP. The requirements are:

No spaces
Only lowercase letters and digits
No special characters except (.),(-),(_) and the user cannot use two or more special characters together
username should not start with special characters
minimum length 6 and maximum 25

this is what I've done so far /^[a-z0-9]{6,25}\S*$/

Wiktor Stribiżew · Accepted Answer · 2021-06-22 21:14:36Z

1

If there can be no special char at the end of the username, use

^(?=.{6,25}$)[a-z0-9]+(?:[._-][a-z0-9]+)*$

Else, if there can be a special char at the end:

^(?=.{6,25}$)[a-z0-9]+(?:[._-][a-z0-9]+)*[._-]?$

See this regex demo.

Details:

^ - start of string
(?=.{6,25}$) - 6 to 25 chars other than line break chars allowed in the string
[a-z0-9]+ - one or more digits or lowercase letters
(?:[._-][a-z0-9]+)* - zero or more occurrences of a ., _ or - followed with one or more digits or lowercase letters
[._-]? - an optional ., _ or -
$ - end of string.

answered Jun 22, 2021 at 21:14

Wiktor Stribiżew

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6 Comments

Tanuj1899 Over a year ago

Thanks for the answer, also I forgot to mention the username should not consist of only numbers how to add this? and where can I learn more about regex codes. thank you.

Wiktor Stribiżew Over a year ago

@Tanuj1899 No numbers only requirement is easy to implement with a negative lookahead: ^(?!\d+$)(?=.{6,25}$)[a-z0-9]+(?:[._-][a-z0-9]+)*$

Wiktor Stribiżew Over a year ago

I do not know your level of regex knowledge :) so that I can only suggest doing all lessons at regexone.com, reading through regular-expressions.info, regex SO tag description (with many other links to great online resources), and the community SO post called What does the regex mean. Also, rexegg.com is worth having a look at.

Wiktor Stribiżew Over a year ago

@Tanuj1899 I also posted some regex articles and am planning to start a Youtube channel with some quick regex demos. I will let you know when I start it.

Tanuj1899 Over a year ago

Thank you for all the resources, I am just getting started with regex. Your channel will be very helpful for me and all others seeking help.

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