Regex: match a string containing numbers and letters, but not a string of numbers only

Question

Question

I would like to be able to use one regex (if possible) to require the string to match [A-Za-z0-9_], but not allow:

• Strings containing only numbers and / or characters.
• Lines beginning or ending with characters
• Several characters next to each other

Really

• test_0123
• t0e1s2t3
• 0123_test
• te0_s1t23
• t_t

Invalid

• t__t
• ____
• 01230123
• _0123
• _test
• _test123
• test_
• test123_

Reasons for the rules

The purpose of this is to filter out the usernames for the website I'm working on. I came to the rules for certain reasons.

• / . /users/#{id} id , . .

• _test , , , .. _test.example.com

• t__t . .. t__t.example.com

Answer 1

, :

/\A(?!_)(?:[a-z0-9]_?)*[a-z](?:_?[a-z0-9])*(?<!_)\z/i

• ([a-z] ).
• ((?!_) (?<!_) ).
• , , ().

: , , lookahead/lookbehind - , - ?: , -, ?: , -:

/\A(?:[a-z0-9]_?)*[a-z](?:_?[a-z0-9])*\z/i

.

Answer 2

, , , , , . ? , , . ( , , . , .)

, ; , ; ; .. .

Answer 3

:

/^(?=[^_])([A-Za-z0-9]+_?)*[A-Za-z](_?[A-Za-z0-9]+)*$/

.

Edit:

. .

Answer 4

"__", :

([A-Za-z]|[0-9][0-9_]*)([A-Za-z0-9]|_[A-Za-z0-9])*

, :

([A-Za-z]|([0-9]+(_[0-9]+)*([A-Za-z|_[A-Za-z])))([A-Za-z0-9]|_[A-Za-z0-9])*

dang, . Telemachus, , , , . .

Answer 5

, , , , . , , , , . :.

x !~ /[^A-Za-z0-9_]|^_|_$|__|^\d+$/

• , , _
• _
• _s

Rails validates_format_of, , , - , , .

Answer 6

(?=.*[a-zA-Z].*)^[A-Za-z0-9](_?[A-Za-z0-9]+)*$

.

, , , . , , .

Answer 7

:

^(([a-zA-Z]([^a-zA-Z0-9]?[a-zA-Z0-9])*)|([0-9]([^a-zA-Z0-9]?[a-zA-Z0-9])*[a-zA-Z]+([^a-zA-Z0-9]?[a-zA-Z0-9])*))$

, , [^ a-zA-Z0-9] [],

Answer 8

/^(?![\d_]+$)[A-Za-z0-9]+(?:_[A-Za-z0-9]+)*$/

, , , . lookhhead - (?![\d_]+$) - ( , ), , .

Answer 9

[A-Za-z][A-Za-z0-9_]*[A-Za-z]

This will work for your first two rules (since the second rule requires a letter at the beginning and end for the second rule, it automatically requires a letter).

I am not sure that the third rule is possible with regular expressions.