Friday 27 April 2018

Github Interview Questions

1. What is the command to write a commit message in Git?

Answer to this is pretty straightforward.
Command that is used to write a commit message is “git commit -a”.
Now explain about -a flag by saying -a on the command line instructs git to commit the new content of all tracked files that have been modified. Also mention you can use “git add<file>” before git commit -a if new files need to be committed for the first time.

2. What is ‘bare repository’ in Git?

You are expected to tell the difference between a “working directory” and “bare repository”.
A “bare” repository in Git just contains the version control information and no working files (no tree) and it doesn’t contain the special .git sub-directory. Instead, it contains all the contents of the .git sub-directory directly in the main directory itself, where as working directory consist of:  
  1. A .git subdirectory with all the Git related revision history of your repo.
  2. A working tree, or checked out copies of your project files.

3. What language is used in Git?

Instead of just telling the name of the language, you need to tell the reason for using it as well. I will suggest you to answer this by saying:
Git uses ‘C’ language. GIT is fast, and ‘C’ language makes this possible by reducing the overhead of run times associated with high level languages.

4. In Git how do you revert a commit that has already been pushed and made public?

There can be two answers to this question and make sure that you include both because any of the below options can be used depending on the situation:
  • Remove or fix the bad file in a new commit and push it to the remote repository. This is the most natural way to fix an error. Once you have made necessary changes to the file, commit it to the remote repository for that I will use
  • git commit -m “commit message”
  • Create a new commit that undoes all changes that were made in the bad commit.to do this I will use a command
  • git revert <name of bad commit>

5. What is the difference between git pull and git fetch?

Git pull command pulls new changes or commits from a particular branch from your central repository and updates your target branch in your local repository.
Git fetch is also used for the same purpose but it works in a slightly different way. When you perform a git fetch, it pulls all new commits from the desired branch and stores it in a new branch in your local repository. If you want to reflect these changes in your target branch, git fetch must be followed with a git merge. Your target branch will only be updated after merging the target branch and fetched branch. Just to make it easy for you, remember the equation below:
Git pull = git fetch + git merge

6. What is Git stash?

According to me you should first explain the need for Git stash.
Often, when you’ve been working on part of your project, things are in a messy state and you want to switch branches for sometime to work on something else. The problem is, you don’t want to do a commit of half-done work just so you can get back to this point later. The answer to this issue is Git stash.
Now explain what is Git stash.
Stashing takes your working directory that is, your modified tracked files and staged changes and saves it on a stack of unfinished changes that you can reapply at any time.

7. What is Git stash drop?

Begin this answer by saying for what purpose we use Git ‘stash drop’.
Git ‘stash drop’ command is used to remove the stashed item. It will remove the last added stash item by default, and it can also remove a specific item if you include it as an argument.
Now give an example.
If you want to remove a particular stash item from the list of stashed items you can use the below commands:
git stash list: It will display the list of stashed items like:
stash@{0}: WIP on master: 049d078 added the index file
stash@{1}: WIP on master: c264051 Revert “added file_size”
stash@{2}: WIP on master: 21d80a5 added number to log
If you want to remove an item named stash@{0} use command git stash drop stash@{0}.

8. How do you find a list of files that has changed in a particular commit?

For this answer instead of just telling the command, explain what exactly this command will do.
To get a list files that has changed in a particular commit use the below command:
git diff-tree -r {hash}
Given the commit hash, this will list all the files that were changed or added in that commit. The -r flag makes the command list individual files, rather than collapsing them into root directory names only.
You can also include the below mentioned point, although it is totally optional but will help in impressing the interviewer.
The output will also include some extra information, which can be easily suppressed by including two flags:
git diff-tree –no-commit-id –name-only -r {hash}
Here –no-commit-id will suppress the commit hashes from appearing in the output, and –name-only will only print the file names, instead of their paths.

9. What is the function of ‘git config’?

First tell why we need ‘git config‘.
Git uses your username to associate commits with an identity. The git config command can be used to change your Git configuration, including your username.
Now explain with an example.
Suppose you want to give a username and email id to associate commit with an identity so that you can know who has made a particular commit. For that I will use:
git config –global user.name “Your Name”: This command will add username.
git config –global user.email “Your E-mail Address”: This command will add email id.

10. What does commit object contains?

Commit object contains the following components, you should mention all the three points present below:
  • A set of files, representing the state of a project at a given point of time
  • Reference to parent commit objects
  • An SHAI name, a 40 character string that uniquely identifies the commit object.

11. How can you create a repository in Git?

This is probably the most frequently asked questions and answer to this is really simple.
To create a repository, create a directory for the project if it does not exist, then run command “git init”. By running this command .git directory will be created in the project directory.

12. How do you squash last N commits into a single commit?

There are two options to squash last N commits into a single commit include both of the below mentioned options in your answer:
  • If you want to write the new commit message from scratch use the following command
  • git reset –soft HEAD~N &&
  • git commit
  • If you want to start editing the new commit message with a concatenation of the existing commit messages then you need to extract those messages and pass them to Git commit for that I will use
  • git reset –soft HEAD~N &&
  • git commit –edit -m”$(git log –format=%B –reverse .HEAD@{N})”

13. What is Git bisect? How can you use it to determine the source of a (regression) bug?

I will suggest you to first give a small definition of Git bisect.
Git bisect is used to find the commit that introduced a bug by using binary search. Command for Git bisect is
git bisect <subcommand> <options>
Now since you have mentioned the command above explain them what this command will do.
This command uses a binary search algorithm to find which commit in your project’s history introduced a bug. You use it by first telling it a “bad” commit that is known to contain the bug, and a “good” commit that is known to be before the bug was introduced. Then Git bisect picks a commit between those two endpoints and asks you whether the selected commit is “good” or “bad”. It continues narrowing down the range until it finds the exact commit that introduced the change.

14. How do you configure a Git repository to run code sanity checking tools right before making commits, and preventing them if the test fails?

I will suggest you to first give a small introduction to sanity checking.
A sanity or smoke test determines whether it is possible and reasonable to continue testing.
Now explain how to achieve this.
This can be done with a simple script related to the pre-commit hook of the repository. The pre-commit hook is triggered right before a commit is made, even before you are required to enter a commit message. In this script one can run other tools, such as linters and perform sanity checks on the changes being committed into the repository.
Finally, give an example, you can refer the below script:
#!/bin/sh
files=$(git diff –cached –name-only –diff-filter=ACM | grep ‘.go$’)
if [ -z files ]; then
exit 0
fi
unfmtd=$(gofmt -l $files)
if [ -z unfmtd ]; then
exit 0
fi
echo “Some .go files are not fmt’d”
exit 1
This script checks to see if any .go file that is about to be committed needs to be passed through the standard Go source code formatting tool gofmt. By exiting with a non-zero status, the script effectively prevents the commit from being applied to the repository.
The Interviewer has not started asking questions on branching yet, so the next set of Git interview questions will be dealing with branching in Git.

15. Describe branching strategies you have used?

This question is asked to test your branching experience with Git so, tell them about how you have used branching in your previous job and what purpose does it serves, you can refer the below mention points:
  • Feature branching
  • A feature branch model keeps all of the changes for a particular feature inside of a branch. When the feature is fully tested and validated by automated tests, the branch is then merged into master.
  • Task branching
  • In this model each task is implemented on its own branch with the task key included in the branch name. It is easy to see which code implements which task, just look for the task key in the branch name.
  • Release branching
  • Once the develop branch has acquired enough features for a release, you can clone that branch to form a Release branch. Creating this branch starts the next release cycle, so no new features can be added after this point, only bug fixes, documentation generation, and other release-oriented tasks should go in this branch. Once it is ready to ship, the release gets merged into master and tagged with a version number. In addition, it should be merged back into develop branch, which may have progressed since the release was initiated.
In the end tell them that branching strategies varies from one organization to another so I know basic branching operations like delete, merge, checking out a branch etc..

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