Understanding git

Avik DasVida Engineering

A quick refresher on graphsBackground:

A

B

D C

A

B

D C

Nodes + Edges = Graph

A

B

D C

Nodes + Edges = Graph

A

B

D C

Nodes + Edges = Graph

A

B

D C

Nodes + Edges = Graph

A

B

D C

A

B

D C

A

B

D C

Directed Edges → Directed Graph

A

B

D C

Directed Edges → Directed Graph

A

B

D C

A

B

D C

cycle

A

B

D C

A

B

D C

A

B

D C

No cycles → Directed Acyclic Graph

A

B

D C

No cycles → Directed Acyclic Graph

A

B

D C

DAG

ABD C

ABD C

DAG → Linearizable

Git objects

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def factorial(x):if x == 0:return 1else:return x * factorial(x - 1)print factorial(6)

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def factorial(x):if x == 0:return 1else:return x * factorial(x - 1)print factorial(6)

066681188100ef24b1ce91a3a3596baffb620051

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def factorial(x):if x == 0:return 1else:return x * factorial(x - 1)print factorial(6)

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def factorial(x): if x == 0: return 1 else: return x * factorial(x - 1)print factorial(6)

066681188100ef24b1ce91a3a3596baffb620051 59d8c4d1b5e8561375aa819adc513529b7ea19b8

TREE

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blob 5b1d3 READMEtree 03e78 libtree cdc8b testblob cba0a test.pyblob 911e7 xdiff

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blob 5b1d3 READMEtree 03e78 libtree cdc8b testblob cba0a test.pyblob 911e7 xdiff

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blob 5b1d3 READMEtree 03e78 libtree cdc8b testblob cba0a test.pyblob 911e7 xdiff

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blob 5b1d3 READMEtree 03e78 libtree cdc8b testblob cba0a test.pyblob 911e7 xdiff

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blob 5b1d3 READMEtree 03e78 libtree cdc8b testblob cba0a test.pyblob 911e7 xdiff

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Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi efficitur ex ex, ac lobortis velit scelerisque

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ac72efa71e90424bdb41dc795609d572ddd88643

COMMIT

COMMIT

tree ac72e parent 84ce1 author Avik Dascommitter Avik Das

Commit message

COMMIT

tree ac72e parent 84ce1 author Avik Dascommitter Avik Das

Commit message

COMMIT

tree ac72e parent 84ce1 author Avik Dascommitter Avik Das

Commit message

COMMIT

tree ac72e parent 84ce1 author Avik Dascommitter Avik Das

Commit message

COMMIT

tree ac72e parent 84ce1 author Avik Dascommitter Avik Das

Commit message

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blob 5b1d3 READMEtree 03e78 libtree cdc8b testblob cba0a test.pyblob 911e7 xdiff

COMMIT

tree ac72e parent 84ce1 author Avik Dascommitter Avik Das

Commit message

COMMIT

tree ac72e parent 84ce1 author Avik Dascommitter Avik Das

Commit message

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blob 5b1d3 READMEtree 03e78 libtree cdc8b testblob cba0a test.pyblob 911e7 xdiff

3f34c01a210400daf86c479b243fe50078c279c1

Working directory → staging → repository

C3C1 C2

HEAD

master

STAGING/INDEXWORKING DIRECTORY COMMANDS

origin/master

C3C1 C2

HEAD

master

STAGING/INDEXWORKING DIRECTORY

README (V1)

COMMANDS

vim README

origin/master

C3C1 C2

HEAD

master

STAGING/INDEXWORKING DIRECTORY

README (V1)

COMMANDS

vim READMEgit add README

origin/master

C3C1 C2

HEAD

master

STAGING/INDEXWORKING DIRECTORY

README (V1)

COMMANDS

vim READMEgit add READMEvim README

README (V2)

origin/master

C3C1 C2

HEAD

master

STAGING/INDEXWORKING DIRECTORY

README (V2)

COMMANDS

vim READMEgit add READMEvim READMEgit add README

origin/master

C3C1 C2

HEAD

master

STAGING/INDEXWORKING DIRECTORY

README (V2)

COMMANDS

vim READMEgit add READMEvim READMEgit add READMEvim READMEREADME (V3)

origin/master

C3C1 C2

HEAD

master

STAGING/INDEXWORKING DIRECTORY

README (V2)

COMMANDS

git diff # between V2 and V3

README (V3)

origin/master

C3C1 C2

HEAD

master

STAGING/INDEXWORKING DIRECTORY

README (V2)

COMMANDS

git diff # between V2 and V3git diff --staged # between V2 # and empty

README (V3)

origin/master

C3C1 C2

HEAD

STAGING/INDEXWORKING DIRECTORY COMMANDS

git commit

README (V3)

C4

masterorigin/master

C3C1 C2

HEAD

STAGING/INDEXWORKING DIRECTORY COMMANDS

git commitgit push# or git push origin master

README (V3)

C4

masterorigin/master

Branching

A B

git clone <url>

origin/master

master

HEAD

A B

git clone <url>git pull

origin/master

master

HEAD

C

A B

git clone <url>git pullgit checkout -b mine

origin/master

master

HEAD

C

mine

A B

git clone <url>git pullgit checkout -b minegit commit

origin/master

master

HEAD

C

mine

X

A B

git clone <url>git pullgit checkout -b minegit commitgit commit

origin/master

master

HEAD

C

mine

X Y

A B

git clone <url>git pullgit checkout -b minegit commitgit commitgit checkout master

origin/master

master

C

mine

X Y

HEAD

A B

git clone <url>git pullgit checkout -b minegit commitgit commitgit checkout mastergit pull

origin/mastermaster

C

mine

X Y

HEAD

D E

A B

git clone <url>git pullgit checkout -b minegit commitgit commitgit checkout mastergit pull

git checkout mine

origin/mastermaster

C

mine

X Y

D E

HEAD

A B

git clone <url>git pullgit checkout -b minegit commitgit commitgit checkout mastergit pull

git checkout minegit merge master

origin/mastermaster

C

X Y

D E

M

mine HEAD

A B

git clone <url>git pullgit checkout -b minegit commitgit commitgit checkout mastergit pull

git checkout minegit merge mastergit commit

origin/mastermaster

C

X Y

D E

M Z

mine HEAD

A B

git clone <url>git pullgit checkout -b minegit commitgit commitgit checkout mastergit pull

git checkout mine

origin/mastermaster

C

mine

X Y

D E

HEAD

A B

git clone <url>git pullgit checkout -b minegit commitgit commitgit checkout mastergit pull

git checkout minegit rebase master

origin/mastermaster

C

X Y

D E

X’

mine

Y’

HEAD

A B

git clone <url>git pullgit checkout -b minegit commitgit commitgit checkout mastergit pull

git checkout minegit rebase mastergit commit

origin/mastermaster

C

X Y

D E

X’ Y’

mine

Z

HEAD

A B

git clone <url>git pullgit checkout -b minegit commitgit commitgit checkout mastergit pull

git checkout minegit rebase mastergit commit

origin/mastermaster

C

X Y

D E

X’ Y’

mine

Z

HEADOnly reachable by SHA1

Rewriting history

A B

master

C1 C2 C3 C4 C5

mine

A B

master

C1 C2 C3 C4 C5

mine

Main changes, split up over two WIP commits

A B

master

C1 C2 C3 C4 C5

mine

Main changes, split up over two WIP commits

Needs some minor touch ups

A B

master

C1 C2 C3 C4 C5

mine

Main changes, split up over two WIP commits

Needs some minor touch ups

Not actually

needed anymore

A B

master

C1 C2 C3 C4 C5

mine

Main changes, split up over two WIP commits

Needs some minor touch ups

Commit message needs work

Not actually

needed anymore

A B

master

C1 C2

git rebase -i master

C3 C4 C5

mine

Main changes, split up over two WIP commits

Needs some minor touch ups

Commit message needs work

Not actually

needed anymore

pick 8af53d3 main feature WIPpick 76d8150 Refactorpick dd69f0c main feature WIP 2pick 974b13e On second thought, not neededpick 508fe0d Build on top of refactor

pick 8af53d3 main feature WIPpick 76d8150 Refactorpick dd69f0c main feature WIP 2pick 974b13e On second thought, not neededpick 508fe0d Build on top of refactor

pick 8af53d3 main feature WIPpick 76d8150 Refactorpick dd69f0c main feature WIP 2pick 508fe0d Build on top of refactor

pick 8af53d3 main feature WIPpick 76d8150 Refactorpick dd69f0c main feature WIP 2pick 508fe0d Build on top of refactor

pick 8af53d3 main feature WIPpick dd69f0c main feature WIP 2pick 76d8150 Refactorpick 508fe0d Build on top of refactor

pick 8af53d3 main feature WIPsquash dd69f0c main feature WIP 2pick 76d8150 Refactorpick 508fe0d Build on top of refactor

pick 8af53d3 main feature WIPsquash dd69f0c main feature WIP 2edit 76d8150 Refactorpick 508fe0d Build on top of refactor

pick 8af53d3 main feature WIPsquash dd69f0c main feature WIP 2edit 76d8150 Refactorreword 508fe0d Build on top of refactor

# This is a combination of 2 commits# The first commit's message is:

main feature WIP

# This is the 2nd commit's message:

main feature WIP

# Please enter the commit message for your changes.

SQUASH

Implement main feature

Usual explanation

# Please enter the commit message for your changes.

SQUASH

Stopped at 56b3bb2562e9ee1a0a984b45e7f2220f1148d189... To be editedYou can amend the commit now, with

git commit --amend

Once you are satisfied with your changes, run

git rebase --continue

EDIT

Build on top of refactor

# Please enter the commit message for your changes.

REWORD

Build on top of refactor

Add some clarifying explanation.

# Please enter the commit message for your changes.

REWORD

A B

master

C1 C2 C3 C4 C5

mine

A B

master

C1 C2 C3 C4 C5

X C2’ C5’

mine

A B

master

C1 C2 C3 C4 C5

X C2’ C5’

mine

Combination of commits C1 + C3

A B

master

C1 C2 C3 C4 C5

X C2’ C5’

mine

Combination of commits C1 + C3Edited from

C2

A B

master

C1 C2 C3 C4 C5

X C2’ C5’

mine

Combination of commits C1 + C3Edited from

C2

Reworded from C5

A B

master

C1 C2

git push --force

C3 C4 C5

X C2’ C5’

mine

Combination of commits C1 + C3Edited from

C2

Reworded from C5

git-rev-parse

git rev-parse HEAD

git rev-parse HEADgit rev-parse HEAD^

git rev-parse HEADgit rev-parse HEAD^git rev-parse HEAD^^

git rev-parse HEADgit rev-parse HEAD^git rev-parse HEAD^^git rev-parse HEAD^^^

git rev-parse HEAD^^^

git rev-parse HEAD~3

git rev-parse master

git rev-parse mastergit rev-parse master^

git rev-parse 757e4cf

Other useful commands

git showgit show <ref>

git resetgit reset --hardgit reset --soft

git add -p

git log <ref>

git reflog

git config

git <verb> --helpgit help <verb>man git-<verb>

Questions?