Tag Archives: Ruby

Ruby Time to Integer does give you seconds since Epoch

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“Time is stored internally as the number of seconds with fraction since the Epoch, January 1, 1970 00:00 UTC.”

 >>require 'time'
 >>Time.parse("January 1, 1970 00:00 UTC").to_i
 => 0

As expected, but nice to verify.

For the reverse, be sure to use Time.at rather than Time.new

>> Time.at(0).to_i
=> 0
>> Time.new(0).to_i
=> -62167201200

Tips for writing command line tools in ruby

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  1. Option parsing: Read this article by Allen Wei on RubyLearning Blog for a great overview.  I recommend sticking with the built-in OptionParser if you want to reduce dependencies.
  2. If you want your code to be loadable so you can access functions and classes in the irb console for testing, use the following pattern: 
    def main
 #option parsing and execution code here
end
if __FILE__ == $0
 main()
end

    This way the main function will only be automatically called if the script is being executed on the command line.
    And in irb, you can call your functions and classes as you see fit for testing without triggering your whole script to run.

    Note that this is similar to the python __main__ test if you are coming from a python background.

  3. Naming without ruby’s.rb extension: You can name your executable without the rb extension if you wish, just be sure to include your shebang (#!)

    To use the user’s default ruby, use:
    #!/usr/bin/env ruby
    But in some cases you may want the specify the path to ruby so you can use macruby or rubycocoa if you are need those frameworks to be available
    #!/usr/bin/ruby

    When testing in irb,
    require 'script-name'
    won’t work without the rb extension, but
    load 'script-name'
    does work.
  4. Use exit codes. When your script fails or needs to communicate status at exit, use standard exit status codes.
    Exit zero for default success status
    exit 0
    Exit any other number for a failure or warning status. You choose the exit codes for your tool, but be sure to document them if they require more explanation than simple success or failure.
    exit 27
  5. Output to stderr using:
    $stderr.puts "error: problem ...."

Read and Write to a Process using Ruby IO popen without blocking

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Once in a while you need to control an interactive command line tool. I kept getting a block when trying to read from a ruby IO popen pipe that was waiting for input. Here is my simple solution/workaround:

sh_process = IO.popen('sh > out.log', 'w')
f = File.open("out.log", "r")
sh_process.puts("ls")
f.read
sh_process.puts("uptime")
f.read
...
f.close

Basically, just create a temp file and read from that. A little hackish, but it works.