Question

I’m trying to find a string with three possible forms:

ab10
ab 10
ab-10

So far I have managed to create this regular expression,

/\s+[a-zA-Z]{2}[-|\s.]?\d{2,3}\s+/

that works for a text like:

start foo ab 10 end foo.

The problem appears when the searched string is at the beginning or at the end of the text like:

ab 10 end foo.

In this case there is no whitespace at the beginning. So I need to match if the string is at the beginning (or end) of the text, but I have no clue how to do it

Can someone give me a little help?

Answer 1

This should fix your problem:

/\b[a-zA-Z]{2}[-|\s.]?\d{2,3}\b/

\b means word boundary, and it asserts that one side (either before or after the current position) is non-word character and the other side is word character (word character as defined by \w).

Note that if you have a string like #ab10., then ab10 will still be matched. But _ab10 will give no match because _ is a word character.

In case you want to assert that the character before and after the string you want to search has to be whitespace character (as defined by \s), OR start/end of the line. I employ the use of look-behind and look-ahead zero-width assertion.

/(?<=^|\s)[a-zA-Z]{2}[-|\s.]?\d{2,3}(?=\s|$)/

The regex above will not find any match in #ab10. or ab10.