This is a simple diceware passphrase generator, implemented in Ruby.
You'll need to download one or both of the available diceware wordlists. The generator expects these to be the raw .asc files with PGP headers/footers in place.
curl 'https://theworld.com/~reinhold/diceware.wordlist.asc' -o diceware.wordlist.asc
curl 'https://theworld.com/~reinhold/beale.wordlist.asc' -o beale.wordlist.asc
dicegen.rb uses the #!/usr/bin/ruby hashbang, so on most systems you merely
need to run, for example:
./dicegen.rb diceware.wordlist.asc 5
This will generate 5 random words from diceware.asc.
If ruby is installed elsewhere, you can either alter the hashbang on line 1, or invoke it directly. Ex:
/usr/local/bin/ruby dicegen.rb diceware.asc 5