Calculate checksum in Ruby

Tue, 13 Oct 2026 09:26:41 +0000

Every developer has faced computing SHA256 checksums for files in their project at some point. For instance, you might need to search for exact file matches or, conversely, prevent duplicate uploads of an existing file. In Ruby, you can use the Digest::SHA256 class for this. But there’s a catch: the built-in method only works for files that already exist on the file system:

require 'digest'
require 'stringio'
require 'tempfile'

src = StringIO.new('Hello, Ruby!')
f = Tempfile.new
f.sync = true
IO.copy_stream(src, f)
Digest::SHA256.file(f.path).hexdigest

However, since a file uploaded by a user is typically represented as a stream (IO) in your web application, Ruby surprisingly doesn’t have a built-in way to calculate a hash directly from a stream. To work around this limitation, you usually have to compute the hash explicitly in a loop, like this:

Checksum on Artem Yegorov

Calculate checksum in Ruby