在PHP中使用正则表达式进行用户名验证

Question

I am trying to validate a USERNAME in PHP using Regular Expression. But I am failed. My pattern is: /[^a-z0-9_]/

Rules:

• username must start number or small letters
• username support number, small letters and _
• the end of username character is not be _

Answer 1

The following pattern will work: ^[a-z0-9][a-z0-9_]*[a-z0-9]$

• ^[a-z0-9]: first character may not be an underscore
• [a-z0-9_]*: all the others may be anything...
• [a-z0-9]$: ...except the last one which can't be an underscore.