git_module3.txt

LECTURE - Checking out commits in a Git repository - Part 1

$ cd git-fast
# created a fresh git repository named "demo-checkout-commit" using initializr.zip
# Build up a commit history by modifying the file robots.txt, say 5 times, and committing each time
# Let us assume we have one commit whose id/hash is 91770af
# the choice of commit id 91770af is arbitrary

# note where the HEAD is now (since HEAD will change later while doing a checkout)
$ git log --oneline

# clear the screen
# The command below will put you in a detached HEAD state.
# HEAD no longer points to a branch; it points directly to a commit.
$ git checkout 91770af
 LECTURE - Checking out commits in a Git repository - Part 2

# you are in detached HEAD state and inside git repository (demo-checkout-commit)
# You can see only commits till commit-id 91770af
$ git log --oneline

# now edit and do a express commit for file robots.txt
# note down your new commit id/hash (Say ID1)
$ git log --oneline

$ git checkout master

# changes made in detached HEAD state is no more there
# the new commit ID1 is not visible
$ git log --oneline

# again you are in detached HEAD state
$ git checkout 91770af

# the new commit ID1 is not visible which means earlier changes...
# in detached HEAD state were not preserved
$ git log --oneline

# now we want to retain our commit i.e, preserve our changes
# make changes in the robots.txt and do an express commit

# create a branch named weird-experiment
$ git branch  weird-experiment

$ git checkout master
# the new commit id is not visible here
# you can check the file robots.txt using cat command also
$ git log --oneline

# new commit id is visible now
# you can examine the file robots.txt using cat command
$ git checkout weird-experiment
LECTURE - Checking out files

# cd to git repository (demo-checkout-commit) used in the previous lecture
$ git log --online

# Let us assume we have the commit-id 91770af

# step-2: examine the current contents of the file
$ cat robots.txt

# now we will able to see the content of the file as at commit-id 91770af
$ git checkout 91770af robots.txt

# this will show the file has been added to the staging area
$ git status

# step-5: examine the contents of the file (should be different from step-2)
$ cat robots.txt

# if we do not want to revert back the file robots.txt
$ git checkout HEAD robots.txt

# you will see a clean working directory
$ git status

# now we want to revert back to the previous version of robots.txt as at commit-id 91770af
$ git checkout 91770af robots.txt
$ git commit -am "reverting back file state to commit 91770af"

# clean working directory
$ git status

# file is reverted and the contents are as seen in step-5
$ cat robots.txt  
 LECTURE - Reverting changes

# cd into repository "undo-demo-git-repo"

# add the text say, "line 5"
$ vim checkoutfile.txt

# modified stage visible
$ git status

# commit the above change
$ git commit -am checkoutfile.txt "commit message..."

$ git log --oneline
$ cat checkoutfile.txt

# Now let's assume the earlier commit is a buggy one and so we will revert it
# revert command introduces a new commit in a safe manner (opens the default editor)
$ git revert HEAD

# check commit history - a new commit for revert
$ git log --oneline

# note the change made earlier has been reverted "line 5" is not visible
$ cat checkoutfile.txt
LECTURE - Resetting Git repository - Part1

# we are in repository git-reset-demo-1 with 2 files goldies-time-table and jimmys-time-table
# the repository has an existing commit history

# now edit file jimmys-time-table and add a line at the end
$ vim jimmys-time-table

# add the change to staging area
$ git add jimmys-time-table

# change in the staging area is visible
$ git status

# undoes changes in the staging area
$ git reset jimmys-time-table

# changes in the staging area are removed; file in modified state
$ git status

# the changed in the working directory is intact
$ cat jimmys-time-table
LECTURE - Resetting Git repository - Part2

# we are in repository git-reset-demo-2 (this repo is clone of git-reset-demo-1)

# edit the file and add one line at the end
$ vim jimmys-time-table

# edit the file and add one line at the end
$ vim goldies-time-table

# files are in modified state
$ git status

# add both files to the staging area
$ git add.

# changes visible in the staging area
$ git status

# "reset" command removes changes in the staging area leaving the working directory intact
$ git reset

# both files in modified state
$ git status

#######################################

# git reset demo using the --hard option
# we are still in git-reset-demo-2 repository(this repo is clone of git-reset-demo-1)

# files are in modified state
$ git status

# add both files to the staging area
$ git add.

# changes visible in the staging area
$ git status

# --hard option removes all changes in the working directory and staging area
$ git reset --hard

# the working directory is clean since all changes have been reset in working dir and staging
$ git status
 LECTURE - Resetting Git repository - Part3

# we are inside git-reset-demo-4 repository (this repo is clone of git-reset-demo-1)

# Let's say, we have 5 commits in the commit history
# let' say, the 5th commit-id (HEAD) is 9166e4f and 4th commit-id is d21a539
$ git log --oneline

# let's reset the repository to 4th commit-id
$ git reset d21a539

# the 5th commit-id(9166e4f) has been removed from history and the HEAD is now at d21a539
$ git log --oneline

# the files are in modified state and changes in the staging area have been removed
# the files are jimmys-time-table and goldies-time-table
$ git status

# now we will commit the above changes in working dir in 2 smaller chunks
$ git add jimmys-time-table
$ git commit -m "commit message....."

# now only goldies-time-table changes are visible in modified state
$ git status

$ git add goldies-time-table
$ git commit -m "commit message....."

# clean working directory
$ git status

$ git log --oneline

# we are in the git-reset-demo-5 repository (this repo is clone of git-reset-demo-1)

# let's say there are 5 commits
$ git log --oneline

# now we will reset to the 3rd commit-id a53f51c (2 commits before HEAD) with the --hard option
# this command will remove 4th & 5th commit-ids as well removed all changes in working dir and staging area
$ git reset --hard a53f51c

# the 4th and 5th commit-ids has been removed from history
$ git log --oneline

# examine the file contents to confirm things
# the lines pertaining to 4th and 5th commit-ids has been removed
$ cat goldies-time-table
$ cat jimmys-time-table
LECTURE - Cleaning Git repository

$ cd git-fast
$ mkdir git-clean-demo
$ cd git-clean-demo

# create an empty repository
$ git init

# create few empty files
$ touch clean-demo-file
$ touch clean-demo-tracked-file

$ git add clean-demo-tracked-file
$ git commit -m "commit tracked file"

# shows clean-demo-file as an untracked file
$ git status

# -n option allows to make a dry run of "git clean" command
$ git clean -n

#################################################

# -f option (-f means force) removes untracked files from the current directory
# so this will remove clean-demo-file
$ git clean -f

#################################################

$ mkdir clean-demo-dir
$ cd clean-demo-dir

# create an untracked file
$ touch clean-demofile-2

$ cd ..

# removes untracked file in path clean-demo-dir
$ git clean -f clean-demo-dir/

#confirm untracked file cleaning
$ cd clean-demo-dir

# "ls" produces no results meaning the untracked file was cleaned
$ ls

#################################################

$ cd ..
$ ls
$ touch clean-demo-file-2
$ ls

# -df option cleans both untracked files and directories
$ git clean -df
$ ls

#################################################

# create .gitignore file and add the file name "clean-demo-file-5"

$ vim .gitignore
$ git add .gitignore
$ git commit -m "committing .gitignore file"

$ touch clean-demo-file-4
$ touch clean-demo-file-5
$ ls -al

# -xf option cleans all untracked files including those mentioned in the .gitignore file
$ git clean -xf

$ ls

Command Summary - pull and push

$ git pull
# cloning generally sets up both the names " origin and master" for you automatically
$ git push origin master