Get available diskspace in ruby

How about simply:

spaceMb_i = `df -m /dev/sda1`.split(/\b/)[24].to_i

where '/dev/sda1' is the path, determined by simply running df

You could use the sys-filesystem gem (cross platform friendly)

require 'sys/filesystem'

stat = Sys::Filesystem.stat("/")
mb_available = stat.block_size * stat.blocks_available / 1024 / 1024

(Ruby) Daniel Berger maintains a lot of gems in this field. To be found there: sys-cpu, sys-uptime, sys-uname, sys-proctable, sys-host, sys-admin, sys-filesystem. They are (AFAIK) multi-platform.