[gyepi]

It's actually quite simple. You write a short shell script to produce the output you need and redo handles the dependencies.

For example, the shell script named "banana.x.do" is expected to produce the content for the file named "banana.x".

When you say

    # redo banana.x

redo invokes banana.x.do with the command:

    sh -x banana.x.do banana.x banana XXX > ZZZ

so banana.x.do is invoked with three arguments and its output is redirected to a file.

   $1 denotes the target file
   $2 denotes the target file without its extension
   $3 is a temp file: XXX, in this case.

banana.x.do is expected to either produce output in $3 or write to stdout, but not both. If there are no failures redo will chose the correct one, rename the output to banana.x and update the dependency database.

If banana.x depends on grape.y, you add the line

    redo-ifchange grape.y

to the banana.x.do, creating a dependency. redo will rebuild grape.y (recursively) when necessary.

The only other commands I haven't mentioned are init and redo-ifcreate, which are obvious and rarely used, respectively.

That's it.