Question

i am stuck at particular problem i have username field where on only alphabets numbers and . – and _ are allowed and should always start with alphabet

here are examples what are accepted

[e-mail]
[e-mail]
[e-mail]
[e-mail]
[e-mail]
[e-mail] 
[e-mail]
[e-mail]

what i have done till now is

[a-zA-Z0-9]+[._-]{1,1}[a-zA-Z0-9][e-mail]

this matches all my requirement except of problem it dosent match

[e-mail]
[e-mail]

but it even matches

[e-mail] 

which is not required i am really not getting how to solve this one thing i tried is

[a-zA-Z0-9]+[._-]{0}[a-zA-Z0-9][e-mail]

but this is also not solving my problem now it accepts everything like

[e-mail] 

which is not required please help me

Answer 1

If you want to make the - or . optional, then you have to replace the {1,1} (quantifier: once) with an ? (quantifier: one or none) here:

 [a-zA-Z0-9]+[._-]?[a-zA-Z0-9][e-mail]

The reason this regex also matches shorter addresses without delimiter -._ is that you don’t assert the whole string, but just some part of it. Use start ^ and end $ anchors:

 ^[a-zA-Z0-9]+[._-]?[a-zA-Z0-9]+@mydomain\.com$