Pack an integer to a byte-sequence string. Discussed in https://discord.com/invite/ruby-518658712081268738 #general. I dedicate this to the Public Domain.

int2bytestr.rb

def int2bytestr(int, bytesize = int.size)
  [
    # Format to hex, left-pad with `0` (big-endian) for `bytesize * 2` nibbles
    sprintf('%0*X', bytesize * 2, int)
  ].pack 'H*' # Pack string of hex chars to string of raw bytes
end

# Demo
print "actual\t"
p int2bytestr(0x4_20_69_de_ad_be_ef_13_37, 10)
print "expect\t"
p %w[0 4 20 69 de ad be ef 13 37].map { _1.hex.chr }.join