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" (e.g. "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!

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" (e.g. "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!

• javascript
• regex

Share Improve this question Follow asked Mar 9, 2021 at 23:36 MeilanMeilan 48411 gold badge1010 silver badges2727 bronze badges

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2 Answers 2

Sorted by: Reset to default 3

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

Try this regex:

testStrings = ["library/History.read", "library/other.read", "library/Geography.read", "library/History.unread", "ebook/hstory.read", "library/StackOverflow.read"]
regex = /library\/[A-Z][^\.]*\.read/

testStrings.forEach(testString => {
  console.log(regex.test(testString) + " - " + testString)
})