Annotate to help learn how it works.

This is an interesting script. I learned a lot from reading it.
Maybe these comments make the script more approachable for people trying to learn how it works.

git-blame-someone-else

@@ -1,19 +1,47 @@
 #!/usr/bin/env bash
 
+# Check that the user has passed in exactly 2 arguments, the AUTHOR and the COMMIT.
+# If they number of arguments is wrong, print out a usage message.
 if [ $# -ne 2 ]; then
   >&2 echo "Usage: $0 <author> <commit>"
   exit 1
 fi
 
+# Assign the author input to the author variable.
+# Author must be formatted like:  John Smith <johnsmith@example.com>
 AUTHOR=$1
+
+# Use perl to find the author name.
+# This is using a regex capture group.
+# Ex: John Smith
 AUTHOR_NAME=$(echo $AUTHOR | perl -wlne '/^(.*?)\s*<.*>$/ and print $1')
+
+# Use perl to find the author email.
+# This is using a regex capture group.
+# Ex: johnsmith@example.com
 AUTHOR_EMAIL=$(echo $AUTHOR | perl -wlne '/^.*\s*<(.*)>$/ and print $1')
+
+# Gets the short version of the commit hash
+# This is needed below so that we can replace the correct commit
+# when editing.
+# Ex: b3d501f
 COMMIT=$(git rev-parse --short $2)
 
 {
-  GIT_SEQUENCE_EDITOR="sed -i -e 's/^pick $COMMIT/edit $COMMIT/'" git rebase -i $COMMIT~1^^ 
+  # Sets the editor to use for updating the sequence of commits.
+  # Normally the sequence editor is your editor (ex: vim).
+  # Here we are using a command that will change pick to edit.
+  # This chooses the right commit for the rebase.
+  GIT_SEQUENCE_EDITOR="sed -i -e 's/^pick $COMMIT/edit $COMMIT/'" git rebase -i $COMMIT~1^^
+
+  # Set the committer name and email, AND the author.
+  # Git tracks both committer and author as they could be different people.
+  # Then we amend the commit in question with the new author and committer.
   GIT_COMMITTER_NAME="$AUTHOR_NAME" GIT_COMMITTER_EMAIL="$AUTHOR_EMAIL" git commit --amend --no-edit --author="$AUTHOR"
+
+  # Finish up the rebase
   git rebase --continue
 } &> /dev/null
 
+# Success message.
 echo "$AUTHOR_NAME is now the author of $COMMIT. You're officially an asshole.";