Using `openssl rand` to generate a random string with a specific character set is not directly supported by the command itself. However, you can use it in combination with other tools like `tr` to achieve your goal. Here's how you can do it:
Understanding `openssl rand`
`openssl rand` generates cryptographically secure pseudo-random bytes. It can output these bytes in various formats, such as hexadecimal or base64, using the `-hex` or `-base64` flags, respectively[1]. However, these formats do not allow you to specify a custom character set directly.
Using `openssl rand` with `tr`
To generate a random string from a specific character set, you can use `openssl rand` to produce random bytes and then filter these bytes using `tr`. Here's an example of how to generate a random string consisting only of lowercase letters and digits:
1. Generate Random Bytes: Use `openssl rand` to generate a sufficient number of random bytes. Since you want to filter these bytes, you'll need more than you need to account for characters that will be discarded.
2. Filter with `tr`: Use `tr` to select only the desired characters from the output.
Here's a command that generates a random string of 10 characters using only lowercase letters and digits:
bash
openssl rand -base64 20 | tr -cd 'abcdefghijklmnopqrstuvwxyz0123456789' | head -c 10
However, this approach might not be efficient if the character set is small because it discards many characters. A better approach is to use `/dev/urandom` directly with `tr`:
```bash
tr -dc 'abcdefghijklmnopqrstuvwxyz0123456789' 9/how-to-decrypt-passwords-generated-by-openssl-rand-base64-20
[8] https://blog.lipsumhub.com/how-to-generate-random-text-in-linux/