Remove not alphanumeric characters from string

Question

I want to convert the following string to the provided output.

Input:  "\\test\red\bob\fred\new"
Output: "testredbobfrednew"

I've not found any solution that will handle special characters like \r, \n, \b, etc.

Basically I just want to get rid of anything that is not alphanumeric. Here is what I've tried...

Attempt 1: "\\test\red\bob\fred\new".replace(/[_\W]+/g, "");
Output 1:  "testedobredew"

Attempt 2: "\\test\red\bob\fred\new".replace(/['`~!@#$%^&*()_|+-=?;:'",.<>\{\}\[\]\\\/]/gi, "");
Output 2:  "testedobred [newline] ew"

Attempt 3: "\\test\red\bob\fred\new".replace(/[^a-zA-Z0-9]/, "");
Output 3:  "testedobred [newline] ew"

Attempt 4: "\\test\red\bob\fred\new".replace(/[^a-z0-9\s]/gi, '');
Output 4:  "testedobred [newline] ew"

One other attempt with multiple steps

function cleanID(id) {
    id = id.toUpperCase();
    id = id.replace( /\t/ , "T");
    id = id.replace( /\n/ , "N");
    id = id.replace( /\r/ , "R");
    id = id.replace( /\b/ , "B");
    id = id.replace( /\f/ , "F");
    return id.replace( /[^a-zA-Z0-9]/ , "");
}

with results

Attempt 1: cleanID("\\test\red\bob\fred\new");
Output 1: "BTESTREDOBFREDNEW"

Working Solution:

Final Attempt 1: return JSON.stringify("\\test\red\bob\fred\new").replace( /\W/g , '');
Output 1: "testredbobfrednew"

Interesting question, the \n in \new is clearly what's tripping this up. I'm not entirely sure how to find and replace that though goes searching for regex on whitespate special chars — Will Buck
– Will Buck, Commented Feb 20, 2012 at 16:19
Are the inputs escaped/how are they assigned? var Input = "\\test\red\bob\fred\new" this string does not contain "red" so your 1st attempt is correct, are you testing against the litteral "\\\\test\\red\\bob\\fred\\new"? — Alex K.
– Alex K., Commented Feb 20, 2012 at 16:21
I guess the question is, do backslashes in your input string represent special characters? (Based on your example output, I'm guessing no.) — Dave
– Dave, Commented Feb 20, 2012 at 16:23

AD7six · Accepted Answer · 2016-04-01 09:40:07Z

669

Removing non-alphanumeric chars

The following is the/a correct regex to strip non-alphanumeric chars from an input string:

input.replace(/\W/g, '')

Note that \W is the equivalent of [^0-9a-zA-Z_] - it includes the underscore character. To also remove underscores use e.g.:

input.replace(/[^0-9a-z]/gi, '')

The input is malformed

Since the test string contains various escaped chars, which are not alphanumeric, it will remove them.

A backslash in the string needs escaping if it's to be taken literally:

"\\test\\red\\bob\\fred\\new".replace(/\W/g, '')
"testredbobfrednew" // output

Handling malformed strings

If you're not able to escape the input string correctly (why not?), or it's coming from some kind of untrusted/misconfigured source - you can do something like this:

JSON.stringify("\\test\red\bob\fred\new").replace(/\W/g, '')
"testredbobfrednew" // output

Note that the json representation of a string includes the quotes:

JSON.stringify("\\test\red\bob\fred\new")
""\\test\red\bob\fred\new""

But they are also removed by the replacement regex.

edited Apr 1, 2016 at 9:40

answered Feb 20, 2012 at 16:23

AD7six

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10 Comments

kylex Over a year ago

This doesn't remove underscores.

Eugene Kuzmenko Over a year ago

@kylex, that's because underscores are considered to be a part of the alphanumeric bunch, for some reason

AD7six Over a year ago

"Because they are the characters typically legal in variable identifiers.". There's no "_" in the question, of course replacing \W with [_\W] (which is used in the question) or similar would remove underscores.

jbmusso Over a year ago

@AD7six, could you please elaborate as to why one should be using JSON.stringify() when the string is coming from an untrusted source? Is there any security concern not to do so? Thanks!

AD7six Over a year ago

@guithor It's not that "one should", or that it affects security at all; If "some string" is being received and for whatever reason it's basically borked( Not apparent from the question why the string is received malformed) - it allows seeing the string for what it is: jsfiddle.net/Z6N7C

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HoldOffHunger · Accepted Answer · 2020-08-04 14:32:22Z

88

All of the current answers still have quirks, the best thing I could come up with was:

string.replace(/[^A-Za-z0-9]/g, '');

Here's an example that captures every key I could find on the keyboard:

var string = '123abcABC-_*(!@#$%^&*()_-={}[]:\"<>,.?/~`';
var stripped = string.replace(/[^A-Za-z0-9]/g, '');
console.log(stripped);

Outputs: '123abcABC'.

edited Aug 4, 2020 at 14:32

HoldOffHunger

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answered Aug 24, 2015 at 22:10

Deminetix

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4 Comments

Tim Over a year ago

input.replace(/\W/g, '') leaves in the _ in a String. @Deminetix is right string.replace(/[^A-Za-z0-9]/g, ''); works better as it removes all non-alphanumeric chars from the String.

AD7six Over a year ago

And yet, no permutation of this answer actually answers the question asked.

v3nt Over a year ago

' & ' becomes '---' at the mo'. Is there a way to build that check in so it only has one hyphen for multiple replacements next to each other?

Mauricio Arias Olave Over a year ago

I tested for a number - i.e: 4,239,721 and I got the desired result = 4239721. Not sure if this the right approach, but, it worked for me by using the regex on this answer: input.replace(/[^A-Za-z0-9]/g, '').

Ledorub · Accepted Answer · 2023-02-05 16:16:52Z

19

You can use \p{L} or \p{Letter} to find letters from any language and \d to find digits.

str.replace(/[^\p{L}\d]/gu, '')

^ to negate character set: not \P{L} and not \d

Flags:

g (global) to perform as many replacements as necessary
u (unicode) to recognize Unicode escape sequences (like \p{L}).

Example:

function removeNonAlphaNumeric(str) {
  return str.replace(/[^\p{L}\d]/gu, '')
}

sequences = [
  'asdé5kfjdk?',
  'uQjoFß^ßI$jI',
  '无论3如何?!',
  'фв@#ео1'
]

for (seq of sequences) {
  console.log(removeNonAlphaNumeric(seq))
}

edited Feb 5, 2023 at 16:16

answered Jan 31, 2022 at 18:38

Ledorub

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Comments

AD7six · Accepted Answer · 2016-05-14 14:06:36Z

11

The problem is not with how you replace the characters, the problem is with how you input the string.

It's only the first backslash in the input that is a backslash character, the others are part of the control characters \r, \b, \f and \n.

As those backslashes are not separate characters, but part of the notation to write a single control characters, they can't be removed separately. I.e. you can't remove the backslash from \n as it's not two separate characters, it's the way that you write the control character LF, or line feed.

If you acutally want to turn that input into the desired output, you would need to replace each control character with the corresponding letter, e.g. replace the character \n with the character n.

To replace a control character you need to use a character set like [\r], as \r has a special meaning in a regular expression:

var input = "\\test\red\bob\fred\new";

var output = input
    .replace(/[\r]/g, 'r')
    .replace(/[\b]/g, 'b')
    .replace(/[\f]/g, 'f')
    .replace(/[\n]/g, 'n')
    .replace(/\\/g, '');

Demo: http://jsfiddle.net/SAp4W/

edited May 14, 2016 at 14:06

AD7six

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answered Feb 20, 2012 at 16:25

Guffa

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2 Comments

Bobby Cannon Over a year ago

I understand everything you are saying but the question still stands and no one has suggested the correct answer yet. The input can be changes but no one has suggest an answer as to how to programmatically change it in JS.

Guffa Over a year ago

@BobbyCannon: I added code that takes your exact input and produces the desired output.

HoldOffHunger · Accepted Answer · 2020-08-04 14:42:28Z

11

You can try this regex:

value.replace(/[\W_]/g, '');

edited Aug 4, 2020 at 14:42

HoldOffHunger

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answered Dec 17, 2015 at 3:55

myrcutio

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Comments

Abdulrahman Hashem · Accepted Answer · 2021-01-31 12:42:50Z

4

To include Arabic letters alongside with English letters, you can use:

// Output: نصعربي
"ن$%^&*(ص ع___ربي".replace(/[^0-9a-z\u0600-\u06FF]/gi, '');

answered Jan 31, 2021 at 12:42

Abdulrahman Hashem

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1 Comment

Lex Over a year ago

Could you elaborate on the inclusion of the code points and why this works? It could be useful more complete

rassar · Accepted Answer · 2022-02-07 20:59:38Z

4

Here is an example that you can use,

function removeNonAlphaNumeric(str){
    return str.replace(/[\W_]/g,"");
}

removeNonAlphaNumeric("0_0 (: /-\ :) 0-0");

edited Feb 7, 2022 at 20:59

rassar

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answered Apr 21, 2020 at 3:12

ravi kishore

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Comments

Roman · Accepted Answer · 2021-06-17 19:14:40Z

2

If you have the case of another language in addition to English you need to add the relative block range from unicode. Here is an example for Cyrillic:

.replace(/[^0-9A-Za-z_\u0400-\u04FF]/gi, '')

edited Jun 17, 2021 at 19:14

answered Jun 1, 2021 at 20:15

Roman

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Comments

Flavio · Accepted Answer · 2019-01-08 02:34:35Z

1

This removes all non-alphanumeric characters, preserves capitalization, and preserves spaces between words.

function alpha_numeric_filter (string) {

  const alpha_numeric = Array.from('abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789' + ' ')

  const json_string = JSON.stringify(string)

  let filterd_string = ''

  for (let i = 0; i < json_string.length; i++) {

    let char = json_string[i]
    let index = alpha_numeric.indexOf(char)
    if (index > -1) {
      filterd_string += alpha_numeric[index]
    }

  }

  return filterd_string

}

const input = "\\test\red\bob\fred\new"
console.log(alpha_numeric_filter(input)) //=> testredbobfrednew

const complex_string = "/_&_This!&!! is!@#$% a%^&*() Sentence+=-[]{} 123:;\|\\]||~`/.,><"
console.log(alpha_numeric_filter(complex_string)) //=> This is a Sentence 123

edited Jan 8, 2019 at 2:34

answered Jun 10, 2018 at 21:56

Flavio

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1 Comment

Flavio Over a year ago

@AD7six thank you for pointing out my error. When I copy pasted the input into WebStrom it automatically added 2 extra backslashes to each existing backslash. I failed to noitice this. input = "\\test\red\bob\fred\new" --> copy_paste = "\\\\test\\red\\bob\\fred\\new".

shift66 · Accepted Answer · 2012-02-20 16:22:06Z

-3

If you want to have this \\test\red\bob\fred\new string, you should escape all backslashes (\). When you write \\test\\red\\bob\\fred\\new your string actually contains single backslashes. You can be sure of this printing your string.
So if backslashes in your string are escaped myString.replace(/\W/g,'') will work normally.

answered Feb 20, 2012 at 16:22

shift66

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3 Comments

Bobby Cannon Over a year ago

If you want to suggest to "you should escape all backslashes ()" then you need to provide an example on how to do it.

shift66 Over a year ago

What do you thing are double backslashes??? and what I mean saying "When you write \\test\\red\\bob\\fred\\new your string actually contains single backslashes." ??? Is this not explaining?

Bobby Cannon Over a year ago

The input is "\\test\red\bod\fred\new" and cannot change. I need a solution for that input string. If you want to show me how to "excape the backslashes" then give an example. We cannot change the input. See the accepted answer. The solution allowed for the input to not change but gave the desired output.

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