As outlined in #239, travis encrypt-file cannot be used for more than one file, because secure environment variables for decryption are overwritten. Overwriting happens unconditionally without any notice about this effect, hence silently destroying working configurations.

As a minimal safety measure, a confirmation by the user should be requested, analogue to the confirmation requested when overwriting an existing encrypted file which is already implemented.

For reference, this is what happens when encrypting a new version of an already existing file

travis encrypt-file test.txt
encrypting test.txt for user/repo
storing result as test.txt.enc
DANGER ZONE: Override existing test.txt.enc? |no|  # Type yes: previous version is overwritten

Something like this would be nice to have:

travis encrypt-file additional-file.txt
encrypting additional-file.txt for user/repo
storing result as additional-file.txt.enc
DANGER ZONE: encrypted_c158cd588669_iv already exists. This indicates there is already an encrypted file present in this repository. More than one encrypted file is not supported. Overwrite existing decryption key? |no|  # Type yes: previous version is overwritten