Trying to create a regular expression that tests for n lowercase characters in a string.

So for a minimum of 2 characters for example, I thought something like ([a-z]){2,} might work.

For the below test the first two are expected to pass:

const min = 2;
const tests = ['a2a#$2', 'a2a#$2a2', 'a2'];
const regex2: RegExp = new RegExp(`([a-z]){${min},}`);
tests.forEach((t) => {
  const valid = regex2.test(t);
  console.log(`t: ${t} is valid: ${valid}`);
});

Thoughts?

CodePudding user response：

[a-z].*[a-z]

Looks for lowercase, then anything or nothing in between, then lowercase again.

Try it out for yourself:

https://www.debuggex.com/

CodePudding user response：

To test if the string has exactly n lower-case letters, attempt to match the following regular expression:

^[^a-z]*(?:[a-z][^a-z]*){n}$

where n is replaced with the desired value.

See Demo for n = 9.

To match at least n lower-case letters use

[^a-z]*(?:[a-z][^a-z]*){n,}

CodePudding user response：

I might go the route of first stripping off all characters other than lowercase letters, then using a length assertion:

var min = 2;
var tests = ['a2a#$2', 'a2a#$2a2', 'a2'];
tests.forEach(e => {
    if (e.replace(/[^a-z] /g, "").length >= min) {
        console.log("MATCH:    "   e);
    }
    else {
        console.log("NO MATCH: "   e);
    }
});

CodePudding user response：

This isn't the most scalable solution, but for 2 lowercase letters, you could do this: .*[a-z].*[a-z].*. Of course, this breaks down if you want to match 1000 lower case letters, you'd have to type [a-z] 1000 times.

CodePudding user response：

From the below, the match function will return the matches array. If there are no matches then it will return null. you can use matches.length to filter the array.

const min = 2;
const tests = ['a2a#$2', 'a2a#$2a2', 'a2'];
tests.forEach((t) => {
  const matches = t.match(/([a-z])/g)||[];
  console.log(`t: ${t} is valid: ${matches.length}`);
});