I would like to have a regular expression that checks if a string contains only upper and lowercase letters, numbers, and underscores.
In Computer Science, an Alphanumeric value often means the first character is not a number but is an alphabet or underscore. Thereafter the character can be 0-9
, A-Z
, a-z
, or underscore (_
).
Here is how you would do that:
Tested under php:
$regex = '/^[A-Za-z_][A-Za-z\d_]*$/'
or take this
^[A-Za-z_][A-Za-z\d_]*$
and place it in your development language.