RegExp - How to check if a string contains a substring in the certain position?

Question

I tried to search this question first but didn't found what I need, here is it:

I have a string like: "substring1/substring2.substring3" (eg "library/History.read")

I need a regular expression to check:

1. the substring1 must be "library"
2. the substring2 must have a captial letter at the beginning
3. the substring3 must be "read"

I'm not familiar with regular expression, the current I wrote is: 'library/([a-zA-Z])\\.(read)' but it is not correct. Please help me, thanks!

Answer 1

There are many ways to solve regex problems, starting from your own attempt here's something that works: :-)

library/([A-Z][a-zA-Z]+)\.(read)

You had three small mistakes:

• . is a character class matching any character except newline. Escape your . like this \. not like this \\. ; and
• Your first capture group was matching exactly one letter. You missed the quantifier. Use the + qunatifier to match one or more.
• As pointed out by Peter, you were missing a character class for your first capital letter

Answer 2

Try this regex:

 testStrings = ["library/History.read", "library/other.read", "library/Geography.read", "library/History.unread", "ebook/hstory.read", "library/StackOverflow.read"] regex = /library\/[AZ][^\.]*\.read/ testStrings.forEach(testString => { console.log(regex.test(testString) + " - " + testString) })