Prerequisites Gem

A ruby gem to make it easy to test that a set of prerequisite conditions are in place.

This can be useful when using ruby as 'glue' code for sysadmin or other tasks.

gem install prerequisites

Or add to your Gemfile:

gem "prerequisites"

This example checks that:

• Environment variables "FOO" and "BAR" are set
• Environment variable "BAZ" is set to the value "whatever"
• Executables "grep", "git", and "kubectl" are in your $PATH
• The shell commands execute successfully

NB: You should ensure that any commands you list in the shell_commands section have no side-effects. These are supposed to be pre-flight checks.

config = {
  environment_variables: [
    "FOO",
    "BAR",
    { "BAZ" => "whatever" }
  ],
  executables_in_path: [
    "grep",
    "git",
    "kubectl"
  ],
  shell_commands: [
    "echo whatever | grep what",
    "kubectl config current-context | grep myk8scluster"
  ]
}

Prerequisites.new(config).check

If any of these conditions are not met, the code will raise an error of class:

• Prerequisites::EnvironmentVariableError
• Prerequisites::ExecutableError
• Prerequisites::ShellCommandError

...depending on the problem.