Regex for IBAN allowing for white spaces AND checking for exact length

Question

I need to check an input field for a German IBAN. The user should be allowed to leave in white spaces and input should be validated to have a starting DE

Answer 1

To allow any amount of spaces anywhere:

^ *D *E( *[A-Za-z0-9]){20} *$

As you want to allow lower letters, also DE might be lower?

^ *[Dd] *[Ee]( *[A-Za-z0-9]){20} *$

• ^ matches the start of the string
• $ end anchor
• in between each characters there are optional spaces *
• [character class] defines a set/range of characters

To allow at most one space in between each characters, replace the quantifier * (any amount of) with ? (0 or 1). If supported, \s shorthand can be used to match [ \t\r\n\f] instead of space only.

Test on regex101.com, also see the SO regex FAQ