SecureRandom string with tr translate showing abundance of underscores?

Question

I am using Devise and attempted to use Devise.friendly_token to generate passwords only to find that it produces undesired special characters. I found that Devise.friendly_token actually uses this method: ``` SecureRandom.urlsafe_base64(15).tr('lIO0', 'sxyz') ``` Attempting to remove the special characters of "-", "=" and "_", I replaced the Devise.friendly_token call with: ``` SecureRandom.urlsafe_base64(15).tr('lIO0=-_', 'sxyzEMU') ``` However, I found that there was an overabundance of "U" characters, having replaced the underscores (obviously some of them are actually "U"). So, I tried this call which eliminated the translate of "_" to "U". ``` SecureRandom.urlsafe_base64(15).tr('lIO0=-', 'sxyzEM') ``` This showed a more reasonable distribution of results, but it still leaves the underscore special character. Can anyone tell me why this is happening and how to resolve it? Example output is: ``` irb(main):017:0> SecureRandom.urlsafe_base64(15).tr('lIO0=-_', 'sxyzEMU').first(8) => "…

Accepted Answer

The `-` character is used by `String#tr` to denote a range of characters. If you meant `-`, you'll need to escape it with a backslash. The example was changing `=` into `E`, `>` into `M`, and all chars from `?` to `_` (including all uppercase letters) into `U`, hence the abundance of U's.

To get the result you expected, use this:

```
SecureRandom.urlsafe_base64(15).tr('lIO0=\-_', 'sxyzEMU')
```

SecureRandom string with tr translate showing abundance of underscores?

Solution

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