Read a File and Redirect the Output to the Same File

To write outputs to a file in a shell, we can use redirection. However, when we read a file and modify the content and redirect to the same original file, we'll get just an empty file. What's going on here? $ cat file bravo delta charlie alpha charlie $ cat file | sort | uniq > file $ cat file # empty file $ Of course, if you redirect to a different file and rename it to the original name, it works as expected.

Read more →

Docker Containers Without a Proper Init Process May Take a Long Time to Terminate

When stopping a container one way or another, like by Ctrl+C or docker stop, Docker sends SIGTERM to the process by default. If the first process (PID = 1) on the container is not a proper init process, the termination may take a long time to be done. It's because processes running as PID 1 are treated differently than usual ones. In Linux, a process running as PID 1 ignores any signal unless the process implements signal handlers on its own.

Read more →

Matchers That Can Take Other Matchers

In RSpec, some matchers can take another matcher as an argument. It is sometimes useful for writing an expectation for a collection. Let's say we want to test that an array contains a string that includes a particular text. We can do that by combining two matchers: include and match as follows. expect(an_array).to include(match(/Lorem/)) # Of course we also could do: # expect(an_array.grep(/Lorem/)).not_to be_empty # or # expect(an_array).to be_any {|item| /Lorem/ === item } I think that in this case, the expectation with include and match is much more concise than the commented-out alternative ways above.

Read more →

Implement and Test in One File with bundler/inline and rspec/autorun

Sometimes I want to create a tiny one-off script that intended to run on a sandbox environment like a Docker container and needs only one file. Most of the time, I also need test frameworks to do some refactoring. It can be done with bundler/inline and rspec/autorun. require 'bundler/inline' gemfile do source '' gem 'rspec' end def doit 'return a string' end require 'rspec/autorun' RSpec.describe '#doit' do example do expect(doit).to be_a(String) end end Usually, Bundler reads the dependencies from Gemfile.

Read more →

Variables with Shell-Style Default in docker-compose.yml

Today I learned that in docker-compose.yml, a variable interpolation with a default can be expressed as ${VAR1:-default value} like shell-style parameter expansion. With parameter expansion, you can do more than setting a default value such as modifying the parameter. However, the supported features in docker-compose.yml are limited to two of them: to set a default variable or to make the parameter mandatory. Let's define VAR_ALPHA with a default value for the example service.

Read more →

Gentaro "hibariya" Terada

Otaka-no-mori, Chiba, Japan
Email me

Loves Ruby, Internet, and Programming.