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SimonJGreen
Asked: 2013-02-04 15:05:08 +0800 CST

Migrating a simple BASH update script from SVN to GIT

  • 772

We used to keep our Nagios config up to date through SVN, with users commiting their changes and a script running every 15 minutes. The script checked for updates, then checked those updates parsed the config check, then reloaded the config. Nice and simple, did the job perfectly.

We recently moved to GIT as part of a wider migration towards GIT for other projects and I'm having difficulty reworking this script to match.

Here is the original SVN version:

cd /usr/local/nagios
RESULT=`svn update | grep Updated | wc -l`
echo $RESULT
if [ "$RESULT" != "0" ]; then
    /etc/init.d/nagios reload
fi
cd -

And here is my best efforts so far with GIT:

cd /usr/local/nagios
RESULT=`git pull 2>&1 | grep Unpacking | wc -l`
echo $RESULT
if [ "$RESULT" != "0" ]; then
    /etc/init.d/nagios reload
fi
cd -

The problem I'm having is I can't seem to get the output parseable so I can match against it. I thought about going a different route by examining the most recent commit in the local working copy, and then checking if the remote most recent commit was different. I can't figure out though how to get this information.

I'm pretty new to GIT and this is driving me nuts, so my huge thanks in advance for any assistance!

bash

4 Answers

  1. Best Answer

    You can check if the tip (a.k.a. HEAD) of the local branch changed before and after you pull.

    cd /usr/local/nagios

before=$(git rev-parse HEAD)
git pull
after=$(git rev-parse HEAD)
if [[ $before != $after ]]; then
  service nagios reload
fi
    • 3

  2. You could use the post-merge hook, which will trigger only when there is a merge on the client side and if there are no conflicts.

    Content of the post-merge:

    #!/bin/bash

/etc/init.d/nagios reload

    Copy the file in .git/hooks on the client side and don't forget to chmod u+x post-merge

    • 1

  3. If you want to know whether there are new changes to fetch, you can compare the output of the following commands:

    $ git show-ref origin/master     # <-- Where this repo thinks "origin/master" is
5bad423ae8d9055d989a66598d3c4473dbe97f8f refs/remotes/origin/master
$ git ls-remote origin master    # <-- Where "origin" thinks "master" is
060bbe2125ec5e236a6c6eaed2e715b0328a9106    refs/heads/master

    If the hashes differ, there are changes to fetch:

    $ git remote update
Fetching origin
...
From github.com:xxxx/yyyy
5bad423..060bbe2  master     -> origin/master
    • 1

  4. Use the checksums displayed by git log. For example:

    cd /usr/local/nagios
git fetch
if [ "$(git log | head -n 1)" != "$(git log origin | head -n 1)" ]; then
    git pull
    /etc/init.d/nagios reload
fi
cd -
    • -1