regex101: PCRE (Legacy) Match Workspace

Pro

\ban ASCII word boundary

Character Class[A-Z]{2}

{2}matches exactly 2 characters from the set below:

A-Zone character from A (65₁₀) to Z (90₁₀) (case sensitive)

Character Class[0-9]{2}

{2}matches exactly 2 characters from the set below:

0-9one character from 0 (48₁₀) to 9 (57₁₀)

Non-Capturing Group(?:[ ]?[0-9]{4}){4}

{4}repeats the group contents below exactly 4 times:

Character Class[ ]?

?matches at most one character from the set below:

the literal (32₁₀ / 40₈ / 20₁₆)

Character Class[0-9]{4}

{4}matches exactly 4 characters from the set below:

0-9one character from 0 (48₁₀) to 9 (57₁₀)

Negative Lookahead(?!(?:[ ]?[0-9]){3})

Non-Capturing Group(?:[ ]?[0-9]){3}

{3}repeats the group contents below exactly 3 times:

Character Class[ ]?

?matches at most one character from the set below:

the literal (32₁₀ / 40₈ / 20₁₆)

Character Class[0-9]

0-9one character from 0 (48₁₀) to 9 (57₁₀)

Non-Capturing Group(?:[ ]?[0-9]{1,2})?

?repeats the group contents below at most once:

Character Class[ ]?

?matches at most one character from the set below:

the literal (32₁₀ / 40₈ / 20₁₆)

Character Class[0-9]{1,2}

{1,2}matches between 1 and 2 characters from the set below:

0-9one character from 0 (48₁₀) to 9 (57₁₀)

\ban ASCII word boundary

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string

25 tokens

Regular Expression

\b[A-Z]{2}[0-9]{2}(?:[ ]?[0-9]{4}){4}(?!(?:[ ]?[0-9]){3})(?:[ ]?[0-9]{1,2})?\b

New

This IBAN looks ok AB12 1234 1234 1234 1234 at first glance
Also this AB12 1234 1234 1234 1234 1 seems fine
And AB12 1234 1234 1234 1234 12 passes


Or without spaces AB123456789012345678
We'll find this AB1234567890123456789 also
Even the longer AB12345678901234567890 matches

Not allowed
------------
AB12 1234 1234 1234 123 (to few numbers)
AB12 1234 1234 1234 1234 123 (to many numbers) 
1234 1234 1234 1234 1234 (starts with numbers)