I am trying to build an efficient regular regression that joins multiple lines with the following constraints to a single line.
- The first lines start with an upper case letter and end with a colon character.
- Other consecutive lines contain 1 to 10 words; the first word should start with an upper case letter. The rest of the words can be mixed case. All the words in a line can contain characters such as ,-./
Positive Samples:
Example 1:
My favorite books are as follows:nA great booknThe Effective Book onscala.ionTest Bookn
Matches:
My favorite books are as follows:nA great booknThe Effective Book onscala.ionTest Bookn
Example 2:
My favorite books are as follows:nA great booknanother sentencenAnother bookn
Matches: lines until first letter of each line is upper case.
My favorite books are as follows:nA great bookn
Negative Sample:
My favorite books are as follows:na great booknanother sentencen
Doesn’t match
I created the following regular expression, but it matches every line regardless of whether it starts with an uppercase.
(^[A-Z].*:)n(^[A-Z].+(?:s+[a-zA-Z0-9,./ ]+){1,10})
If the above regex matched the expected lines, I would replace n with a space and comma.
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You may use this regex to get your matches:
^[A-Z][^:n]*:n(?:[A-Z][w,./-]*(?:h+[w,./-]+){0,9}n)+
RegEx Demo
RegEx Details:
^: Start new line[A-Z]: Match an upper case letter[^:n]*: Match 0 or more characters that are not::n: Match colon followed by a line break(?:: Start non-capture group[A-Z][w,./-]*: Match first word that must start with an uppercase letter(?:h+[w,./-]+){0,9}: Match 0 to 9 of other words sepaeated with 1+ whitespacesn: Match a line break
)+: End non-capture group. Repeat this group 1+ times
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First off use this site to test things: https://regex101.com/
It will save you so much time.
This should get you want you want, although you’ll need to make sure you’re not using a multiline flag so that it doesn’t match your negative case.
^([A-Z](.*h?){0,9}n?)+
You can replace .* with a more restricted pattern for a single line (excluding the first character) like this:
^(([A-Z])([w:.,-]*h?){0,9}n?)+
What’s important here is that you do need a starting match but you also need a n ending match to make sure you partially match your negative case. I added the h to only match tabs and spaces but not newlines.
Here’s a demo with it
The biggest issues with your regex are:
- It wasn’t matching anything without a multiline flag. If you use the website I linked you can see that the second start of string meta character does not work without the
mflag. That’s because it will only match the start of the entire string unless you tell it to match the start of each line (that’s what the multiline aspect means) .+(?:s+[a-zA-Z0-9,./ ]+)this is redundant and not actually serving you what you think..+is basically matching the entire line except the last word (based on the space) and then it matches[a-zA-Z0-9,./ ]the last word or symbol and then repeats for 15 lines.
Problem 2 isn’t that bad because it does do what you want for the most part but what I provide should be lean enough that you build off of it you run into problems later. Again you’re original regex could if you remove the second ^ but I imagine something might mess up because there’s a lot of unnecessary things in it.
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