Word diff two markdown files in git and output the result formatted for Pandoc CSS

diff_script

#!/bin/zsh

filename=$1
if [[ -z $filename ]] || [[ $filename == 'help' ]]
then
        echo 'usage: diff_script file.markdown [old_revision] [new_revision]'
        echo '  old_revision defaults to HEAD^'
        echo '  new_revision defaults to current file (HEAD if unchanged)'
        exit
fi

old_revision=$2
new_revision=$3

old_filename=`mktemp`
new_filename=`mktemp`

if [ -z $old_revision ] # if old revision specified
then
        git show "HEAD^":$filename > $old_filename        # just take previous revision
else
        git show $old_revision:$filename > $old_filename  # find that specific revision in history and use it
fi

if [ -z $new_revision ] # if new revision specified
then
        cp $filename $new_filename                        # just take current version in the file system
else
        git show $new_revision:$filename > $new_filename  # find that specific revision in history and use it
fi

# consider stripping Markdown comments here

# actual diffing of the files
diff_markdown_filename=`mktemp`
echo "diff markdown filename: $diff_markdown_filename"
wdiff -w '<span class="diff-added">' -x '</span>' -y '<span class="diff-removed">' -z '</span>' $new_filename $old_filename > $diff_markdown_filename
pandoc -s --html5 --smart -c my.css $diff_markdown_filename

# cleanup
# commenting out for debugging and they are temp files anyway
#rm $old_filename $new_filename $diff_markdown_filename