Generate Random String in Postman

Question

I'm new at postman an im trying to generate a random string with letters(A-Z) and numbers(0-9). The string should have 20 points. I don't know how to set the Body and the pre req. I know that the Request must be POST. I have no idea how to start.

Palila

Answer 1

You can add scripts to the Pre-request Script to create this value.

This function will create the random value from the characters in the dataset and it will be 20 characters in length - The length can be adjusted when calling the function with your desired min and max values.

function randomString(minValue, maxValue, dataSet = 'abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ') {
    if (!minValue) {
        minValue = 20;
        maxValue = 20;
    }

    if (!maxValue) {
        maxValue = minValue;
    }

    let length = _.random(minValue, maxValue),
        randomString = "";

    for (let i = 0; i < length; i++)
        randomString += dataSet.charAt(Math.floor(Math.random() * dataSet.length));
    return randomString;
}

pm.variables.set('randomString', randomString());

Adding a basic body like this is how you can use the randomly generated value:

{
    "randomValue": "{{randomString}}"
}

When the request is sent, it will execute the function in the Pre-request Scripts tab and set the value as a local variable, this will then be used in the body of the request:

Outsize

Answer 2

Per postman's docs you should be able to use {{$randomAlphaNumeric}} to generate a single character. $randomPassword seems to just generate 15 random alpha numeric characters so something like:

{{$randomPassword}}{{$randomAlphaNumeric}}{{$randomAlphaNumeric}}{{$randomAlphaNumeric}}{{$randomAlphaNumeric}}{{$randomAlphaNumeric}}

should give you 20 random characters without writing much code. This is a little terse, you could also just use the $randomAlphaNumberic selector 20 times.

Casing

If "randomness" is not really important, most of time I will use the combination of $randomPassword (15) and $randomCreditCardMask (4 digits) and $randomAlphaNumeric (1 char). We can combine so we can get our desired length. – Laryngeal

Do like that you posted the link to the docs, I managed to find a better answer, As it gives random first and last names out of the box. – Hatch

Answer 3

Code for your Pre-request Script tab in Request:

    function randomString(length=1) {
        let randomString = "";
        for (let i = 0; i < length; i++){
            randomString += pm.variables.replaceIn("{{$randomAlphaNumeric}}");
        }
        return randomString;
    }
    
    STRING_LEN = 1000
    pm.variables.set('randomString', randomString(STRING_LEN));

Just set the STRING_LEN to desired value.
Test it by using expression {{randomString}} i.e. in URL:

    https://httpbin.org/anything?string={{randomString}}

Result:

Provocation

Answer 4

Here's another cleaner solution that works just fine in Postman

// Generate a random 10-character string using built-in dynamic variable and substring
const randomString = pm.variables.replaceIn('{{$randomUUID}}').substring(0, 10);
pm.environment.set('partner_transaction_id', randomString);
console.log('partner_transaction_id:', randomString);

Marathi