Patch and diff

This is a technique to

• Reduce the size of install scripts
• Make them more forward compatible for the future
• Make them more robust

The Idea

The idea is simple: install by hand, make changes to make it work, then compare against the pristine sources, generating a patch that later does automatically what you did by hand

• Setup the app for installation as a webapp (say in html). Save a pristine copy as html.orign
• Make changes in html/ only
• Find out the diff of what you made:

   diff -r -N -b -u html.orig html > app-patch.diff

• This then can go into the install script as follows:

   patch -p0 -E << EOF
   .... contents of app-patch.diff here ....
   EOF

Testing the patch ahead of time

It is strongly encouraged that you test the patch before attempting trial-and-error runs in the install script, which can be time consuming and error prone. This is basically simulating the install script applying the patch.

To do this, do this:

    mv html html.modified
    cp -a html.orig html
    mv html.orig html.pristine

(the last step is to prevent patch from accidentally patching html.orig)

then try your patch against html dir (which is now like the original):

    patch -p0 -E < app-patch.diff

Doing this will save you a lot of trial-and-error in the installer.

References

• Good reference tutorial on diff and patch
• Ten minute guide to diff and patch