A random string is a sequence of characters that is generated randomly, rather than being determined by a set pattern or predetermined sequence. Random strings are often used as passwords, keys, or identifiers, and they can be generated using a variety of methods.
Generating random strings in Bash can be a handy tool, whether you’re creating temporary file names, generating passwords, or testing. Bash provides several ways to generate random strings using built-in utilities and commands. In this article, we’ll explore various methods to achieve this and provide examples for each.
1. Using $RANDOM Variable:
Bash shell provides a special variable called `$RANDOM` that returns a random number between 0 and 32767. You can utilize this variable to produce a random string.
Example:
echo $RANDOM
However, this will only return a number. If you want a string with characters, you might have to get a bit more creative.
echo $(date +%s%N) | sha256sum | head -c 10
This command uses the current timestamp (in nanoseconds) and pipes it to the sha256sum command, then truncates the result to the first 10 characters.
2. Using /dev/urandom:
`/dev/urandom` is a device file that provides a source of cryptographically secure random numbers.
To generate a random string of length 10:
cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w 10 | head -n 1
Here’s what’s happening in the above command:
- cat /dev/urandom: Outputs random bytes from /dev/urandom.
- tr -dc ‘a-zA-Z0-9’: Deletes characters that are not alphanumeric.
- fold -w 10: Wraps the output to 10 characters wide, effectively giving us lines of 10 characters each.
- head -n 1: Takes only the first line.
3. Using openssl
To generate a random string in Bash, you can use the `openssl` command and the `base64` encoding function. Here is an example of how you can generate a random string of length 10:
openssl rand -base64 10
This will generate a random string of length 10 using base64 encoding. The output will be a string of characters that includes letters, numbers, and special characters.
You can also use the `tr` command to remove any characters that you don’t want to include in your random string. For example, to generate a random string of length 10 that only includes uppercase letters and digits, you can use the following command:
openssl rand -base64 10 | tr -dc 'a-zA-Z0-9'
This will generate a random string of length 10 that only includes uppercase letters and digits.
You can adjust the length of the random string by changing the number passed to the `-base64` option. For example, to generate a random string of length 20, you can use the following command:
openssl rand -base64 20 | tr -dc 'a-zA-Z0-9'
This will generate a random string of length 20 that only includes uppercase letters and digits.
4. Using pwgen:
`pwgen` is a tool specifically designed to generate passwords, which means it can produce random strings. If you don’t have it installed, you can usually get it via your package manager (apt-get, yum, brew, etc.)
Example:
pwgen 10 1
This will generate a random string of length 10.
5. Using Bash Arrays:
You can combine bash arrays with `$RANDOM` to produce a random string.
Example:
ARRAY=('a' 'b' 'c' 'd' 'e' 'f' 'g' 'h' 'i' 'j' 'k' 'l' 'm' 'n' 'o' 'p' 'q' 'r' 's' 't' 'u' 'v' 'w' 'x' 'y' 'z')
RAND_STR=""
for i in {1..10}; do
RAND_STR+="${ARRAY[$RANDOM % ${#ARRAY[@]}]}"
done
echo $RAND_STR
This will produce a random string of 10 lowercase letters.
Conclusion
Random strings are useful because they are difficult to guess or predict, which makes them suitable for use as passwords or other forms of authentication. They can also be used to randomly assign identifiers to objects or records in a database, which can help to ensure that the identifiers are unique and not predictable.
This tutorial helped you to generate random strings in bash shell scripts and Linux command line interface.