Saturday, September 19, 2015

Version Control For Scripts

Running a full blown version control system such as subversion or CVS for Bash scripts is a bit of overkill.  Most people don't use any version control at all on scripts and revert back to the ancient way of saving multiple copies of the files.

The inevitable result is a mess of files called script1, script2, script.ok, script.bad... and then after a few days, you cannot remember which is which.

Fortunately, there is an ancient, light weight versioning system that is very easy to set up and which is perfect for the single user case: RCS.

Setup RCS

It is probably already installed (try whereis rcs), otherwise do:
# yum install rcs

In your script directory, make a directory to keep the archives:
$ mkdir RCS

Edit each script and add the $Id$ keyword to the top, right underneath the familiar #! /bin/bash command:
#! /bin/bash
#$Id$

That will substitute your name, date, time and version number of the file upon checkout, so you always know which version of the script you got.

Check In

As soon as you made an important change, check the file in, with ci:
$ ci scriptname

Type a proper description of the change, it is for your own benefit, when you have to look at a problem, possibly years later.

The file will disappear!


Check Out

Check it out again with co:
$ co scriptname 

By default you get the latest version.  You can also check out older versions using the -r parameter and switch between versions to see which one works best, without losing anything, since they are all in the archive file.

Important Tricks

If you are the only person working on the scripts, then remove strict locking.  This will make your life much easier:
$ rcs -U *

Now you can check files in with the -u option, so they don't disappear and gets checked out again immediately:
$ ci -u scriptname
 
You can also set an alias (add to the bottom of ~/.bashrc), to save you some more typing, so that you never have to use the co command again, just ci filename:
$ alias ci='ci -u'

That is pretty much all there is to it.

Do read the man pages of ci, co and rcs for details on what to do when the inevitable happens and you want to look at the logs and revert to an older version of a script.


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