Regex to match only letters

In python, I have found the following to work:

[^\W\d_]

This works because we are creating a new character class (the []) which excludes (^) any character from the class \W (everything NOT in [a-zA-Z0-9_]), also excludes any digit (\d) and also excludes the underscore (_).

That is, we have taken the character class [a-zA-Z0-9_] and removed the 0-9 and _ bits. You might ask, wouldn't it just be easier to write [a-zA-Z] then, instead of [^\W\d_]? You would be correct if dealing only with ASCII text, but when dealing with unicode text:

\W

Matches any character which is not a word character. This is the opposite of \w. > If the ASCII flag is used this becomes the equivalent of [^a-zA-Z0-9_].

^ from the python re module documentation

That is, we are taking everything considered to be a word character in unicode, removing everything considered to be a digit character in unicode, and also removing the underscore.

For example, the following code snippet

import re
regex = "[^\W\d_]"
test_string = "A;,./>>?()*)&^*&^%&^#Bsfa1 203974"
re.findall(regex, test_string)

Returns

['A', 'B', 's', 'f', 'a']

For PHP, following will work fine

'/^[a-zA-Z]+$/'

So, I've been reading a lot of the answers, and most of them don't take exceptions into account, like letters with accents or diaeresis (á, à, ä, etc.).

I made a function in typescript that should be pretty much extrapolable to any language that can use RegExp. This is my personal implementation for my use case in TypeScript. What I basically did is add ranges of letters with each kind of symbol that I wanted to add. I also converted the char to upper case before applying the RegExp, which saves me some work.

function isLetter(char: string): boolean {
  return char.toUpperCase().match('[A-ZÀ-ÚÄ-Ü]+') !== null;
}

If you want to add another range of letters with another kind of accent, just add it to the regex. Same goes for special symbols.

I implemented this function with TDD and I can confirm this works with, at least, the following cases:

    character | isLetter
    ${'A'}    | ${true}
    ${'e'}    | ${true}
    ${'Á'}    | ${true}
    ${'ü'}    | ${true}
    ${'ù'}    | ${true}
    ${'û'}    | ${true}
    ${'('}    | ${false}
    ${'^'}    | ${false}
    ${"'"}    | ${false}
    ${'`'}    | ${false}
    ${' '}    | ${false}

Lately I have used this pattern in my forms to check names of people, containing letters, blanks and special characters like accent marks.

pattern="[A-zÀ-ú\s]+"

JavaScript

If you want to return matched letters:

('Example 123').match(/[A-Z]/gi) // Result: ["E", "x", "a", "m", "p", "l", "e"]

If you want to replace matched letters with stars ('*') for example:

('Example 123').replace(/[A-Z]/gi, '*') //Result: "****** 123"*

/^[A-z]+$/.test('asd')
// true

/^[A-z]+$/.test('asd0')
// false

/^[A-z]+$/.test('0asd')
// false