How to find and restore “rewritten” git commits?

Question

For some reason I have git repo with commits of code which were rewritten to its previous state. Like this:

• initial code was "Hello world!" and it was committed in repo;
• on some day it was changed to "Bye-bye world!" and it was committed in repo;
• on some day later this code was reverted on HDD to its initial state ("Hello world!") and committed in repo.

I need to find somehow such commits. It can be not sequential commits but the commits which "rewrites" code to its previous state.

How can I do this?

Answer 1

You can use git bisect .

git-bisect
Find by binary search the change that introduced a bug

gitbisect is a tool to search and fund out in which commit your code was changed. Its very simple to use it and its very powerful as well.

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How does bisect works?

Bisect simply go over the history log and perform a binary search.

a binary search or half-interval search algorithm finds the position of a specified input value (the search "key") within an array sorted by key value.

More about Binary search

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Git bisect sample

// Start the bisect operation
git bisect start 

// mark the current as bad or good depends on the content of your given
// file. In your case since you want to find the commit who modified your
// code to "Hello world!" lets assume the current file is the bad state
git bisect bad 

// Assume 100 commits ago it was before your change (or give a sha if you
// know where its was ok last time
git bisect good HEAD~100

// Now git will split the history and start looping over it.
... do your tests and decide if its good or bad (check the file content)

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How to automate the bisect ?

Adding the run flag which allow you to automate the search.
The run gets a script which is being executed on each checkout commit.

git bisect run my_script arguments

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Bisect run exit codes:

Note that the script (my_script in the above example) should exit with code 0 if the current source code is good, and exit with a code between 1 and 127 (inclusive), except 125, if the current source code is bad.

Any other exit code will abort the bisect process.

It should be noted that a program that terminates via "exit(-1)" leaves $? = 255, (see the exit(3) manual page), as the value is chopped with "& 0377".

The special exit code 125 should be used when the current source code cannot be tested. If the script exits with this code, the current revision will be skipped