How to auto include the newest git commit metadata into the commited files?

Question

I aim to add a rudimentary change log to the top of every file, e.g.:

# Changelog: 
# Last Modified on: 31.2.2020
# Last Modified by: Arthur Dent
# Last Modification: "After a Trillian tries, it works"
# File created: 01.01.1970

def whale2pot(args) ....

Now, in order to not have to do that manually, I would like to include the output of

git log -1

to the files concerned by this commit. (Not sure whether including the commit message is smart though..)

One way of doing this is via a bash script, which prepends the output of the above to the file(s). But this modifies the file(s), and the repo would never be actually up to date.

Hence: Is there a way to "overload" git commit or somehow sneak this in without git noticing?

Thanks in advance =)

Answer 1

After some tinkering, I chose this format (here it is for .m files):

%% ------------------------------------------------  
%  
% Created on:       <date_of_creation>  
% Author:           <author>  
%  
% Last modifier:    <modifier>  
% Last modified:    <date_of_last_mod>  
% On Branch:        <branch>  
%  
%%-------------------------------------------------

... and realized that I don't need the commit meta-data to achieve my goal. I get:

• the dates from $(date)
• the Author/Modifier from $(git config user.name)
• the current branch from $(git rev-parse --abbrev-ref HEAD)

Still I followed @LeGEC's approach of having one script which does two things, as follows:

• insert_changelog.sh: This ensures that every untracked file with a specific extension receives a changelog. Further, it fills the static information of <date_of_creation> and <author>.
• update_changelog.sh: This script updates the latter 3 fields of every tracked and modified file.

For the time being, I run this manually before running git add <modified files>.

I append the code below. This is my first bash scripting experience so feel free to point out what could be improved <=)

---

insert_changelog.sh:

#!/bin/bash

#If there are no .m files for which this would apply, suppress the this notification (If i get that right)
shopt -s nullglob

#Act on untracked files 
files=($(git ls-files --others --exclude-standard))
for item in ${files[*]}
do
    #For time being, only consider matlab files
    if [[ $item == *.m ]]
    then
        #Check whether the header already exists
        read -r first_line < $item 
        first_cl_line="%% ------------------------------------------------"
        if [ "$first_line" = "$first_cl_line" ]
        then
            continue
        else
            #Include Changelog into file
            cat changelog_template.txt > tempfile
            cat $item >> tempfile 
            mv tempfile $item

            #Fill in static fields of inception date and author
            sed -i "3,4d" $item
            sed -i "2 a % Created on:       $(date)" $item
            sed -i "3 a % Author:           $(git config user.name)" $item

            #Update current changelog
            ./update_changelog.sh $item
        fi
    fi
done;

update_changelog.sh:

#!/bin/bash
USER=$(git config user.name)  
BRANCH=$(git rev-parse --abbrev-ref HEAD)  
#Remove outdated lines and replace with updated ones.  
   for item in $(git ls-files -m)  
   do  
       sed -i "5,8d" $item  
       sed -i "5 a % Last Modifier:    $USER" $item  
       sed -i "6 a % Last Modified:    $(date)" $item  
       sed -i "7 a % On Branch:        $BRANCH" $item  
       sed -i "8 a %" $item  
   done;