Git merge behaviour

git-merge-behaviour.sh

git init merge_test
# Initialized empty Git repository in /vagrant/merge_test/.git/

cd merge_test
echo "First commit." > a_file
git commit -am "First commit."

git log
# commit eb4173dbd9589057e4fa0df089de781b33db9f5c (HEAD -> master)
# Author: vagrant <[email protected]>
# Date:   Thu Nov 9 03:19:43 2017 +0000
# 
#     First commit.

git branch feature
git branch develop
git checkout feature
# Switched to branch 'feature'

echo "Second commit." >> a_file
git commit -am "Second commit."
git log
# commit e73018f4843087bd3be23dbb469ffaec8d32ed1d (HEAD -> feature)
# Author: vagrant <[email protected]>
# Date:   Thu Nov 9 03:28:32 2017 +0000
# 
#     Second commit.
# 
# commit eb4173dbd9589057e4fa0df089de781b33db9f5c (master, develop)
# Author: vagrant <[email protected]>
# Date:   Thu Nov 9 03:19:43 2017 +0000
# 
#     First commit.

git checkout develop
git merge feature
Updating eb4173d..e73018f
# Fast-forward
#  a_file | 1 +
#  1 file changed, 1 insertion(+)

git log
# commit e73018f4843087bd3be23dbb469ffaec8d32ed1d (HEAD -> develop, feature)
# Author: vagrant <[email protected]>
# Date:   Thu Nov 9 03:28:32 2017 +0000
# 
#     Second commit.
# 
# commit eb4173dbd9589057e4fa0df089de781b33db9f5c (master)
# Author: vagrant <[email protected]>
# Date:   Thu Nov 9 03:19:43 2017 +0000
# 
#     First commit.

# FAST FORWARD MERGE MEANS NO MERGE COMMIT SO HISTORIES ARE IDENTICAL.

git branch release
git checkout release
echo "Third commit." >> a_file
git commit -am "Third commit."
git checkout master
git merge release
# Fast-forward
#  a_file | 2 ++
#  1 file changed, 2 insertions(+)

git log
# commit a3db5c679d8106c2bc6b2c84680e6c594b6b53bd (HEAD -> master, release)
# Author: vagrant <[email protected]>
# Date:   Thu Nov 9 03:35:23 2017 +0000
# 
#     Third commit.
# 
# commit e73018f4843087bd3be23dbb469ffaec8d32ed1d (feature, develop)
# Author: vagrant <[email protected]>
# Date:   Thu Nov 9 03:28:32 2017 +0000
# 
#     Second commit.
# 
# commit eb4173dbd9589057e4fa0df089de781b33db9f5c
# Author: vagrant <[email protected]>
# Date:   Thu Nov 9 03:19:43 2017 +0000
# 
#     First commit.

# ONCE AGAIN A FAST FORWARD MERGE SO NOT DIFFERENCE IN HISTORIES.

# BUT MEANWHILE DEVELOP HAS PROGRESSED.
git checkout develop
echo "Fourth commit." >> a_file
git commit -am "Fourth commit."
git merge master
# Auto-merging a_file
# CONFLICT (content): Merge conflict in a_file
# Automatic merge failed; fix conflicts and then commit the result.

# MERGE CONFLICT BECAUSE SAME LINE WAS CHANGED.
cat a_file
# First commit.
# Second commit.
# <<<<<<< HEAD
# Fourth commit.
# =======
# Third commit.
# >>>>>>> master

# CURRENTLY ON DEVELOP SO 'HEAD' REPRESENTS CHANGED ON THAT BRANCH.
# RESOLVE MERGE CONFLICTS...
cat a_file
# First commit.
# Second commit.
# Third commit.
# Fourth commit.
git commit -a
git log
# commit 761bf516a89ae8ff71c179b26d5bf8f5904e2c7b (HEAD -> develop)
# Merge: a8080f0 a3db5c6
# Author: vagrant <[email protected]>
# Date:   Thu Nov 9 03:45:40 2017 +0000
# 
#     Merge branch 'master' into develop
# 
# commit a8080f05208451b8defc705ae153259cde415d68
# Author: vagrant <[email protected]>
# Date:   Thu Nov 9 03:39:05 2017 +0000
# 
#     Fourth commit.
# 
# commit a3db5c679d8106c2bc6b2c84680e6c594b6b53bd (release, master)
# Author: vagrant <[email protected]>
# Date:   Thu Nov 9 03:35:23 2017 +0000
# 
#     Third commit.
# 
# commit e73018f4843087bd3be23dbb469ffaec8d32ed1d (feature)
# Author: vagrant <[email protected]>
# Date:   Thu Nov 9 03:28:32 2017 +0000
# 
#     Second commit.
# 
# commit eb4173dbd9589057e4fa0df089de781b33db9f5c
# Author: vagrant <[email protected]>
# Date:   Thu Nov 9 03:19:43 2017 +0000
# 
#     First commit.

# GIT LOG IS IN CORRECT ORDER BUT HISTORIES HAVE NOW DIVERGED BECAUSE DEVELOP HAS AN EXTRA 'MERGE COMMIT'.

# NOW MERGE BACK INTO MASTER.
git branch release-two
git checkout release-two
echo "Fifth commit." >> a_file
git commit -am "Fifth commit."
git checkout master
git merge release-two
# Fast-forward
#  a_file | 2 ++
#  1 file changed, 2 insertions(+)

# MEANWHILE ON DEVELOP FILE HAS CHANGED AGAIN BUT NOT THE SAME LINE THIS TIME.
git checkout develop
vim a_file
cat a_file
# 1st commit.
# Second commit.
# Third commit.
# Fourth commit.

git commit -am "Sixth commit."
git merge master
# FILE OPENS FOR SAVING WITH MERGE COMMIT MESSAGE PRE-POPULATED. SAVE.
# Auto-merging a_file
# Merge made by the 'recursive' strategy.
#  a_file | 1 +
#  1 file changed, 1 insertion(+)

# THIS TIME IT USED 'RECURSIVE' RATHER THAN 'FAST FORWARD' MERGE STRATEGY.
git log
# commit 007d58f791c1585a47a999bcdcc72262e89299f2 (HEAD -> develop)
# Merge: 709a3cb f1825df
# Author: vagrant <[email protected]>
# Date:   Thu Nov 9 03:55:44 2017 +0000
# 
#     Merge branch 'master' into develop
# 
# commit 709a3cb6bd09dc6d12102c0813c1003b57fd332a
# Author: vagrant <[email protected]>
# Date:   Thu Nov 9 03:55:12 2017 +0000
# 
#     Sixth commit.
# 
# commit f1825df7011d7085c8b158ee55461b6f1780bca4 (release-two, master)
# Author: vagrant <[email protected]>
# Date:   Thu Nov 9 03:52:25 2017 +0000
# 
#     Fifth commit.
# 
# commit 761bf516a89ae8ff71c179b26d5bf8f5904e2c7b
# Merge: a8080f0 a3db5c6
# Author: vagrant <[email protected]>
# Date:   Thu Nov 9 03:45:40 2017 +0000
# 
#     Merge branch 'master' into develop
# 
# commit a8080f05208451b8defc705ae153259cde415d68
# Author: vagrant <[email protected]>
# Date:   Thu Nov 9 03:39:05 2017 +0000
# 
#     Fourth commit.
# 
# commit a3db5c679d8106c2bc6b2c84680e6c594b6b53bd (release)
# Author: vagrant <[email protected]>
# Date:   Thu Nov 9 03:35:23 2017 +0000
# 
#     Third commit.
# 
# commit e73018f4843087bd3be23dbb469ffaec8d32ed1d (feature)
# Author: vagrant <[email protected]>
# Date:   Thu Nov 9 03:28:32 2017 +0000
# 
#     Second commit.
# 
# commit eb4173dbd9589057e4fa0df089de781b33db9f5c
# Author: vagrant <[email protected]>
# Date:   Thu Nov 9 03:19:43 2017 +0000
# 
#     First commit.

# EVEN THOUGH THERE WERE NO MERGE CONFLICTS A NEW 'MERGE COMMIT' WAS STILL CREATED.