regex to remove certain characters at the beginning and end of a string

Question

Let's say I have a string like this:

...hello world.bye

But I want to remove the first three dots and replace .bye with !

So the output should be

hello world!

it should only match if both conditions apply ( ... at the beginning and .bye at the end)

And I'm trying to use js replace method. Could you please help? Thanks

Answer 1

Your regex would be

 const rx = /\\.\\.\\.([\\s\\S]*?)\\.bye/g const out = '\\n\\nfoobar...hello world.bye\\nfoobar...ok.bye\\n...line\\nbreak.bye\\n'.replace(rx, `$1!`) console.log(out) 

In English, find three dots, anything eager in group, and ending with .bye.

The replacement uses the first match $1 and concats ! using a string template.

Answer 2

First match the dots, capture and lazy-repeat any character until you get to .bye , and match the .bye . Then, you can replace with the first captured group, plus an exclamation mark:

 const str = '...hello world.bye'; console.log(str.replace(/\\.\\.\\.(.*)\\.bye/, '$1!')); 

The lazy-repeat is there to ensure you don't match too much, for example:

 const str = `...hello world.bye ...Hello again! Goodbye.`; console.log(str.replace(/\\.\\.\\.(.*)\\.bye/g, '$1!')); 

Answer 3

You don't actually need a regex to do this. Although it's a bit inelegant, the following should work fine (obviously the function can be called whatever makes sense in the context of your application):

function manipulate(string) {
    if (string.slice(0, 3) == "..." && string.slice(-4) == ".bye") {
        return string.slice(4, -4) + "!";
    }
    return string;
}

(Apologies if I made any stupid errors with indexing there, but the basic idea should be obvious.)

This, to me at least, has the advantage of being easier to reason about than a regex. Of course if you need to deal with more complicated cases you may reach the point where a regex is best - but I personally wouldn't bother for a simple use-case like the one mentioned in the OP.

Answer 4

An arguably simpler solution:

const str = '...hello world.bye'
const newStr = /...(.+)\.bye/.exec(str)

const formatted = newStr ? newStr[1] + '!' : str

console.log(formatted)

If the string doesn't match the regex it will just return the string.