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Archive for December 17th, 2012

A story of PROMPT_COMMAND and RVM

December 17th, 2012 14 comments

It’s a bit over a year as I work as RVM maintainer with over one and half year (19 months) of contributing to the project.

As I work on the project it was always improved, we spent a lot of time responding to user requests. At first I was helping Wayne E. Seguin the original author and later I took over as maintainer. We have been working hard in our free time to improve the first ruby environment switcher. We also had a lot of ideas how to make things better, but because it was our free time we were not always able to make all the ideas happen even implementing them would be as simple as just few lines change.

Today I want to share history of one of that ideas, automatic environment switching using a shell hook PROMPT_COMMAND => http://www.tldp.org/HOWTO/Bash-Prompt-HOWTO/x264.html, it is very easy idea allowing to execute piece of code every time user prompt is to be displayed. It was supposed to solve some limitations of overwriting builtin change directory command – cd, especially not rereading project file when it’s updated.

Before we were able to implement it a new project come to life – rbenv, it was also intended to do the environment switching but a lot simpler. Among of a lot of promotional keywords rbenv was accusing rvm of overwriting cd, which is considered harmful by rbenv author. To not feed the propaganda of a new tool rvm team has dropped all ideas related to accusations from rbenv. Among other interesting ideas rvm dropped also the idea of using PROMPT_COMMAND.

As time passes a lot of new tools was created to do the same thing – switching ruby environments. One of the tools is chruby, one of the most minimalistic implementations. I was helping from time to time the author with shell code, with understanding the problem of switching environment or just discussing various aspects of the tools we work on.

Of course there was also a need for automated switching of environment in chruby, the author started with cd function implementation as this is one of the easiest ways to archive this functionality. But then I have remembered of PROMPT_COMMAND and proposed use of it, which after quick test appeared to be better solution.

Seeing the idea working I have decided to implement it also for rvm, as initially expected this is a lot simpler code and solves some of the issues. We could have this code available for rvm users one year ago, possibly we could have a lot more of good solutions if the problems were discussed instead of throwing accusations as it was done by rbenv author.

So I wanted to sum the situation here, I wanted to disapprove the method of promoting opensource in cost of other opensource software without bringing discussion, without opening not a single ticket for the project. This are practices that you use fighting “corporate” world, as opensource authors we can choose to work together put aside all the politics, and do our work together for common benefit.

On the end I would thank postmodern the author of chruby for bringing up the discussion and working towards standardizing our software.

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