#!/usr/bin/env ruby is not found in cron

The problem is that the environment isn't what you expect.

You don't say whether the cron is running as your user, or as root, but, in either case, you can test to see what the environment looks like by adding another cron entry of:

* * * * * /usr/bin/env > /path/to/your/home/directory/env.txt 

Let that run once, then pull it out, and look at the file.

Instead of using /usr/bin/env to try to find a Ruby to run your code, define the Ruby explicitly:

* * * * * /path/to/the/ruby/you/want /usr/local/src/hello/hello.rb >> /usr/local/src/hello/hello.log 2>&1 

You can figure out which Ruby you want by using:

which ruby 

Alternately, instead of relying on /usr/bin/env in your #! line, define your Ruby there.

Using /usr/bin/env ruby in your code is a convenience when you're using something like RVM or rbenv, and switching between versions of Ruby. It's not a good choice when you're putting something into "production", whether it's on your machine in your own account, or on a production host running as root.

If you are on Linux or Mac OS, try man 5 crontab for more information. Also, "Where can I set environment variables that crontab will use?" should be very useful.