I'm trying to use a Regex pattern (in Java) to find a sequence of 3 digits and only 3 digits in a row. 4 digits doesn't match, 2 digits doesn't match.
The obvious pattern to me was:
"\b(\d{3})\b"
That matches against many source string cases, such as:
">123<"
" 123-"
"123"
But it won't match against a source string of "abc123def" because the c/1 boundary and the 3/d boundary don't count as a "word boundary" match that the \b class is expecting.
I would have expected the solution to be adding a character class that includes both non-Digit (\D) and the word boundary (\b). But that appears to be illegal syntax.
"[\b\D](\d{3})[\b\D]"
Does anybody know what I could use as an expression that would extract "123" for a source string situation like:
"abc123def"
I'd appreciate any help. And yes, I realize that in Java one must double-escape the codes like \b to \b, but that's not my issue and I didn't want to limit this to Java folks.
You should use lookarounds for those cases:
(?<!\d)(\d{3})(?!\d)
This means match 3 digits that are NOT followed and preceded by a digit.