This script can be used on a git repository to extract the contributors with the purpose of listing potential copyright holders on a given codebase. If invoked with a sub-path, it will only consider that file or directory.

authors.sh

#!/bin/sh

# Syntax: authors.sh [ PATH ]

LC_CTYPE=C
LANG=C

# Get all files in HEAD, skipping the bootloaders directory
files=$(git ls-tree -r --name-only HEAD "$1" | grep -v "^bootloaders" | grep -v "^firmwares" | xargs grep -Il "")

# Get the list of authors with e-mail addresses
IFS=$'\n'
authors=$(for f in $files; do
    git blame -w -C --porcelain "$f" | sed -n \
        -e '/^author /{ s/^author //; s/,/ /g; h; }' \
        -e '/^author-mail /{ s/^author-mail //; H; x; s/[<>]//g; s/\n/,/p; }'
    git log "$f" | grep Co-authored-by | sed -Ee 's/[[:space:]]*Co-authored-by: (.+) <(.+)>/\1,\2/'
done)

# Remove duplicates based on e-mail address
authors=$(printf "%s" "$authors" | sort -u -t, -k2,2)

# Get the count of relevant contributions for each author
# Relevant contributions are the total number of added or changed lines
# belonging to chunks of at least 3 lines. Please note that even a
# one-line contribution might be copyrightable so this threshold is
# aribtrary. YMMV.
# Also, this may raise false positives because it also considers
# contributions that are not visible in HEAD anymore.
authors=$(for a in $authors; do
    printf "%s," "$a"
    email=$(printf "$a" | cut -d, -f2)
    git log --author="$email" --pretty=tformat: --numstat "$1" | awk 'BEGIN {s=0} $1 > 2 {s+=$1} END {print s}'
done | sort -t, -k3,3 -nr)

# Convert commas to tabs
# (It was much easier to use commas in the above commands)
authors=$(printf "%s" "$authors" | tr , $'\t')

echo "$authors"

The script does not consider that IP may later be moved to a different file by another author:

$ git init
Initialized empty Git repository in E:/deleteme/foo-repo/.git/

$ export GIT_AUTHOR_NAME="Foo Contributor" GIT_AUTHOR_EMAIL="foo@example.com"

$ echo "some
> important
> contribution" > some-file

$ git add some-file && git commit -m "Make important contribution"
[main (root-commit) 0f5ae77] Make important contribution
 Author: Foo Contributor <foo@example.com>
 1 file changed, 3 insertions(+)
 create mode 100644 some-file

$ export GIT_AUTHOR_NAME="Bar Maintainer" GIT_AUTHOR_EMAIL="bar@example.com"

$ cp some-file other-file && echo "" > some-file

$ git add . && git commit -m "Reorganize repository"
[main 42f64fb] Reorganize repository
 Author: Bar Maintainer <bar@example.com>
 2 files changed, 4 insertions(+), 3 deletions(-)
 create mode 100644 other-file

$ /tmp/authors.sh .
Bar Maintainer  bar@example.com 3

Moving the IP from one file to another doesn't change the fact that "Foo Contributor <foo@example.com>" is still a copyright holder, yet the script does not recognize them as such.