How to Generate Random String/Characters in Golang?

We might want to generate random strings or even sets of characters to perform some operations or add certain string-related functionality into an application. We can randomly get a character from a set of characters, randomize the order of characters of a given string or generate a random string. We can use the rand, encoding package in Golang. In this article, we will see how to generate random strings in Golang.

Get a Random Character From string

Let's say we want to get a random alphabet from a to z, we just can't hard code them to the specific values, we need a pseudo-random way to get a character from a string. We will use the rand module to choose a random character from the given string. 

Firstly, we create a string with all the sets of characters in it. This will simply be a string in Go lang as we define it in double-quotes.

charset := "abcdefghijklmnopqrstuvwxyz"

The above string can be anything you like to get a random character from. 

Next up, we need to randomly choose a character from the string, we can do that by importing the rand package in Golang. The rand function has a function called Intn, which generates a random number between 0 (inclusive) to the provided number(non-inclusive). So it basically takes an integer (say n) as an argument and returns any random number from 0 to n-1. 

So with this, we can get the random index of the string and access the character with that index. the provided argument to the Intn function will be the total length of the string. 

charset[rand.Intn(len(charset))]

We will store the above output in a variable and hence we have a random character selected from a string. We also need to make sure we generate a different seed each time the program is run, to that we can use the time.Now function from time package in Golang. We need to convert the time in seconds we do that by using the Unix function or UnixNano/UnixMilli/UnixMicro functions, which convert the time in seconds, nanoseconds, milliseconds, and microseconds respectively, simply using Unix will also work fine.   

Below is a script that depicts the working of the above explanation.

// Go program to generate random characters from the string
package main

import (
    "fmt"
    "math/rand"
    "time"
)

func main() {

    rand.Seed(time.Now().UnixNano())

    // String
    charset := "abcdefghijklmnopqrstuvwxyz"

    // Getting random character
    c := charset[rand.Intn(len(charset))]

    // Display the character
    fmt.Println(string(c))
}

Output:

Generated character:q

Generate a Random String

We can generate a random string, using some random number generation and character code arithmetic. We will first define the length of the string, it can be anything you like. Next, we need to create a byte slice of predefined size. A byte is a datatype in go, you can learn more about it on the official docs. We will then iterate over the byte slice and populate it with random characters between a specific range. As a byte in Golang accepts ASCII character code, we might refer to the ASCII table for understanding the code for characters we want to generate from. 

length := 4

ran_str := make([]byte, length)

We will generate only Upper case alphabets so, we will assign each character the code 65 and add a random integer between 0 to 25 i.e. we will be able to generate codes from 65 to 90. As we will have 26 codes for 26 alphabets and now if you see that 65 to 90 is the character code for A to Z characters in ASCII. thus, we will populate the byte slice with these randomly generated characters as bytes.

for i := 0; i < length; i++ {

ran_str[i] = ran_str(65 + rand.Intn(25))

}

After the byte slice has been generated we can get the slice in a string variable by concatenating the byte slice with string. 

str := string(ran_str)

Also, we need to make sure we get a new seed every time we run the script, so as to generate unique random numbers, we can do that by using the time.Now function. The time.Now function gets us the current time, we simply convert that into seconds using the Unix function as it is a viable seed format. The Unix function returns the time in seconds( passed time in seconds from 1st Jan 1971). 

rand.Seed(time.Now().Unix())

Thus, by summarizing the above explanation, we can write the script to generate a random string. 

// Go program to generate a random string
package main

import (
    "fmt"
    "math/rand"
    "time"
)

func main() {

    rand.Seed(time.Now().Unix())
    length := 4

    ran_str := make([]byte, length)

    // Generating Random string
    for i := 0; i < length; i++ {
        ran_str[i] = ran_str(65 + rand.Intn(25))
    }

    // Displaying the random string
    str := string(ran_str)
    fmt.Println(str)
}

Output:

SNOC

Shuffle a String

We can even shuffle characters of the string in Golang, we can use the Shuffle function in the rand module in Golang. Provided a string, we can write a swap function that will swap two characters in a string. We will first define a string that can be anything that you wished to shuffle. Next, we can declare a rune slice that we will use to store the new shuffled string. 

str := "geeksforgeeks"

shuff := []rune(str)

Using the random Shuffle function, we can store the shuffled characters into the newly created run slice. The Shuffle function takes two arguments, the length of string and the swap function. The swap function will simply take two indices(integers) and inside the function, we can swap the two characters using the parsed indices in this case i and j th index in the string. 

rand.Shuffle(len(shuff), func(i, j int) {

shuff[i], shuff[j] = shuff[j], shuff[i]

})

So, using the above logic and explanation, we can create the script by also adding the time.Now function, each time the Shuffle function is called, it should have a new seed. Now in order to generate a new seed for the execution of the program, we will use the current time as a seed. We can generate the seed by using time.Now function and then get the Unix seconds(time in seconds passes since 1st Jan 1970).

rand.Seed(time.Now().Unix())

// Go program to Shuffle a String
package main

import (
    "fmt"
    "math/rand"
    "time"
)

func main() {
    rand.Seed(time.Now().Unix())

    str := "geeksforgeeks"

    shuff := []rune(str)

    // Shuffling the string
    rand.Shuffle(len(shuff), func(i, j int) {
        shuff[i], shuff[j] = shuff[j], shuff[i]
    })

    // Displaying the random string
    fmt.Println(string(shuff))
}

Output:

 eggsekekeorsf