llama-tts : input from stdin

[marcoStocchi]

In case of missing text prompt, tts tries to detect an input redirection to the stdin and reads it.
This enables piping text to llama-tts, input redirection and heredocuments.
In case of empty text prompt the program exits, avoiding useless runtime.

[ngxson]

Personally I don't quite like this feature, because you can easily redirect the output from another command to llama-tts by placing the input into an arg, for example:

llama-tts -p "$(cat my_text.txt)"

# this also works with multiple lines input

Beside, the llama-tts-* examples are experimental, I prefer keep them simple by not having too many non-related features