Sunday, 21 July 2019

Git- Part 3: Git Staging, Viewing Changes, Push and Pull, Dangers of Git Pull

Git Basics: Staging Files

● Command: git add <path|file>

● Staging Area (aka Index) allows you to selectively choose which files

will be committed and which will NOT (e.g debug files)

● .gitignore files can be used to automatically exclude files

 

Git Basics: Excluding Files with.gitignore

● Each line specifies a file pattern to ignore.

● Many ways to implement .gitignore

(e.g. can have per-directory .gitignore files)

● But most common is to put in top-level directory of repo.

[anandg anandg@ /home/anandg (master)]$ cat .gitignore

venv/

*DS_Store

keep

.idea

*.log

*.pid

*.pyc

*.swp

*~

.#*

\#*

Git Basics: Checking File Status

● Command: git status

● This command shows files that are tracked by the repo…

and files that are not tracked by the repo (i.e. untracked)

● This command also shows files that are staged for next committal

 

Git Basics: Committing Files

● Command: git commit -m

● Commits ONLY files in the Staging Area / Index

● Committing creates a SNAPSHOT of the entire repo.

GIT doesn't use patches / deltas to track changes but rather entire snapshots

 

Git Basics: Viewing Commit History

● Command: git log
● Run this command to see the commit history of the repo (for the given branch)

[anandg anandg@ /home/anandg (master)]$ git log

commit 46968d4d20b636ada053571202317c01a4eb4d50 (HEAD -> master)

Author: Anand G anandg@google.com

Date: Wed Oct 4 02:17:11 2017 -0400

Demo of GIT workflow

commit fc813cde051518f7343d386799e24f279df7c039

Author: Anand G anandg@google.com

Date: Mon Oct 2 18:36:22 2017 -0400

Modified TestScript.py to allow for log demo.

 

Git Basics: Viewing a Particular Commit

● Command: git show

● Run this command to see all diffs from that commit

● The sha1hash is used to identify a commit.

● GIT actually uses SHA1 hashes to verify the integrity of the files.

● Immediately, GIT knows if the content of the a file is corrupt or not.

 

NOW,

Previously, we saw the "commit fc813cde051518f7343d386799e24f279df7c039"

To run this command, git show fc81

 

Git Basics: Publishing Changes to Git Server

● Command: git push [ [] ]

● This command pushes your changes (over the network) to a remote repository ( often the origin )

● origin is a shorthand notation of the repository from which you cloned

 

[anandg anandg@ /home/anandg (master)]$ git config -l | grep origin

remote.origin.url=git@github:testrepo.git

remote.origin.fetch=+refs/heads/:refs/remotes/origin/

branch.master.remote=origin

 

Git Basics: Pulling Changes from Git Server

● Command: git pull [ [] ]

● This command pulls your updates (over the network) to your local repository.

● Contrary to popular belief, git pull is NOT the inverse of git push. The git fetch command is. Both git push and git fetch don't involve any merging.

● This command is really two commands built into one:

git fetch + git merge

● More on this soon...

 

[anandg anandg@ /home/anandg/testrepo (master)]$ git pull

remote: Counting objects: 226, done.

remote: Compressing objects: 100% (126/126), done.

remote: Total 226 (delta 119), reused 180 (delta 100)

Receiving objects: 100% (226/226), 116.80 KiB | 1.07 MiB/s, done.

Resolving deltas: 100% (119/119), done.

From github:testrepo

4fc8080..3e06595 master -> origin/master

Updating 4ed9080..3b07595

Fast-forward

bin/lib/file1.py | 19 ++-

bin/tools/file2.py | 25 ++-

.

.

.

lib/file3.py | 2 +-

lib/file4.py | 132 ++++++++++++++

requirements.txt | 1 +

24 files changed, 1007 insertions(+), 252 deletions(-)

create mode 100755 bin/file5.py

 

Git Basics: Dangers of Git Pull

● The one BIG downside of git pull is that it does NOT allow you to review any changes before it merges into your current branch

● git fetch updates your remote tracking branches under refs/remotes/ but not your local branches under refs/heads

● git merge always merges into your current branch. Be careful when running git pull.

● If the project practice code reviews, this isn't as big of a problem. But it is * STRONGLY * recommend to do one or the other (i.e. code reviews or fetch reviews)

● Workflow

git fetch origin/

git log origin/

git diff origin/

git merge origin/

● We'll discuss more later with branches...

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