understanding-git/demoscript

#!/usr/bin/env bash

set -euo pipefail
scriptloc=$(cd $(dirname "${BASH_SOURCE[0]}") && pwd)

replace() {
keyword=$1
string=$2
python << END
with open("${scriptloc}/slides.md") as slides:
    content = slides.read()

string = """${string}"""
with open("${scriptloc}/slides.md", "w") as slides:
    slides.write(content.replace(r"${keyword}", string))
END
}

mdprint() {
    cmd=$*
    echo '```bash'
    echo '$' ${cmd}
    eval ${cmd}
    echo '```'
}

tmpdir=$(mktemp -d)
pushd ${tmpdir}

# delete temporary directory on script exit
trap "rm -fr ${tmpdir}" 0

# Initialise repository
mdprint git init

git config --local user.name "Achilleas Koutsou"
git config --local user.email "ak@example.com"


# No objects here yet
mdprint tree -F .git/objects

# Add a README and commit
mdprint 'echo "# Understanding Git: Presentation slides repository" > README.md'
mdprint git add README.md
firstcommit=$(mdprint 'git commit -m "Initial commit: Add README"')
replace "::firstcommit::" "${firstcommit}"

# Check the object store again
firstobjectstore=$(mdprint tree -F .git/objects)
replace "::firstobjectstore::" "${firstobjectstore}"

filepaths1=$(find .git/objects -type f)

# git cat-file on each object
for path in ${filepaths1}; do
    prefix=${path:13:2}
    rest=${path:16}
    full=${prefix}${rest}
    type=$(git cat-file -t ${full})
    cattype=$(mdprint git cat-file -t ${full})
    catprint=$(mdprint git cat-file -p ${full})
    replace "::catt${type}1::" "${cattype}"
    replace "::catp${type}1::" "${catprint}"
done

# Let's make one more commit so we can see the parent
mdprint 'echo -e "# Understanding Git\n\n> Achilleas Koutsou\n\n2018-11-14" > slides.md'
mdprint git add slides.md
mdprint 'git commit -m "Add first presentation slide"'

# Check the object store again
mdprint tree -F .git/objects

secondobjectstore=$(mdprint find .git/objects -type f)
replace "::secondobjectstore::" "${secondobjectstore}"

filepaths2=$(find .git/objects -type f)

# git cat-file on each *new* object
for path in ${filepaths2}; do
    if echo ${filepaths1} | grep ${path} &> /dev/null; then
        continue
    fi
    prefix=${path:13:2}
    rest=${path:16}
    full=${prefix}${rest}
    mdprint git cat-file -t ${full}
    mdprint git cat-file -p ${full}
    type=$(git cat-file -t ${full})
    cattype=$(mdprint git cat-file -t ${full})
    catprint=$(mdprint git cat-file -p ${full})
    replace "::catt${type}2::" "${cattype}"
    replace "::catp${type}2::" "${catprint}"
    if git cat-file -p ${full} | grep "Understanding Git" &> /dev/null; then
        slidesfirstver=${full}
    fi
done

echo "--------------------------"
# Add a new slide
mdprint 'echo -e "\n\n# Part 1\n## Porcelain and Plumbing" >> slides.md'
mdprint git add slides.md
mdprint 'git commit -m "Add second presentation slide"'

# Check the object store again

thirdobjectstore=$(mdprint find .git/objects -type f)
replace "::thirdobjectstore::" "${thirdobjectstore}"
filepaths3=$(find .git/objects -type f)

# git cat-file on each *new* object
for path in ${filepaths3}; do
    if echo ${filepaths2} | grep ${path} &> /dev/null; then
        continue
    fi
    prefix=${path:13:2}
    rest=${path:16}
    full=${prefix}${rest}
    mdprint git cat-file -t ${full}
    mdprint git cat-file -p ${full}
    type=$(git cat-file -t ${full})
    cattype=$(mdprint git cat-file -t ${full})
    catprint=$(mdprint git cat-file -p ${full})
    replace "::catt${type}3::" "${cattype}"
    replace "::catp${type}3::" "${catprint}"
done

mdprint git cat-file -p ${slidesfirstver}

mdprint git cat-file -t HEAD
mdprint git cat-file -t master
catpmaster=$(mdprint git cat-file -p master)
replace "::catpmaster::" "${catpmaster}"

mdprint git cat-file -t master~1
mdprint git cat-file -t master~1:
mdprint git cat-file -p master~1:slides.md

mdprint git cat-file -p master~1:README.md
mdprint git cat-file -p master:README.md

rpheada=$(mdprint git rev-parse HEAD)
replace "::rpheada::" "${rpheada}"
rpmastera=$(mdprint git rev-parse master)
replace "::rpmastera::" "${rpmastera}"

catpheada=$(mdprint git cat-file -p HEAD)
replace "::catpheada::" "${catpheada}"
rpheadtld1a=$(mdprint git rev-parse HEAD~1)
replace "::rpheadtld1a::" "${rpheadtld1a}"

catpmastertld1clna=$(mdprint git cat-file -p master~1:)
replace "::catpmastertld1clna::" "${catpmastertld1clna}"
catpmastertld1rdma=$(mdprint git rev-parse master~1:README.md)
replace "::catpmastertld1rdma::" "${catpmastertld1rdma}"

mdprint git branch demo-code
rpmasterdemohead=$(mdprint git rev-parse master demo-code HEAD)
replace "::rpmasterdemohead::" "${rpmasterdemohead}"

mdprint git checkout demo-code

mdprint 'echo "#!/usr/bin/env bash" > demoscript'
mdprint 'chmod +x demoscript'
mdprint 'git add demoscript'
mdprint 'git commit -m "Add demoscript"'

rpmasterb=$(mdprint git rev-parse master)
replace "::rpmasterb::" "${rpmasterb}"
rpdemob=$(mdprint git rev-parse demo-code)
replace "::rpdemob::" "${rpdemob}"
rpheadb=$(mdprint git rev-parse HEAD)
replace "::rpheadb::" "${rpheadb}"

mdprint git checkout master
rpmasterc=$(mdprint git rev-parse master)
replace "::rpmasterc::" "${rpmasterc}"
rpdemoc=$(mdprint git rev-parse demo-code)
replace "::rpdemoc::" "${rpdemoc}"
rpheadc=$(mdprint git rev-parse HEAD)
replace "::rpheadc::" "${rpheadc}"

mdprint ls

mdprint 'echo -e "\n\n# Part 2\n## What is Git?" >> slides.md'
mdprint git add slides.md
mdprint 'git commit -m "Add third presentation slide"'

rpmasterdemod=$(mdprint git rev-parse master~1 demo-code~1)
replace "::rpmasterdemod::" "${rpmasterdemod}"

gitloga=$(mdprint git log -n 2)
replace "::gitloga::" "${gitloga}"

gitlogb=$(mdprint 'git log --pretty=format:"Commit: %h | Parent: %p | Tree: %t %n Message: %s%n"')
replace "::gitlogb::" "${gitlogb}"

gitlogc=$(mdprint 'git log --graph --oneline master demo-code')
replace "::gitlogc::" "${gitlogc}"

exit

# ---------------

mdprint git log --graph master demo-code

mdprint 'git log --graph --pretty=format:"Commit: %H%n    Message: %s%n    Parent: %P%n    Tree: %T%n%n" master demo-code'

git log --reverse --pretty=format:"Commit: %H%n    Message: %s%n    Parent: %P%n    Tree: %T%n%n"