If you need to name a blob by name, you can't trust Git to honor the
current working directory. If you are in a subdir, git show
HEAD^:file won't work unless you prepend the subdirectory name.
But there's a sort of basename for absolute paths within a Git repo:
git ls-tree --name-only --full-name HEAD file
This honors $PWD and thus returns a pathname that's unique across
the repository. You can build a simple "diff to previous version"
script with this now:
#!/bin/sh
test ! -z "$1" || exit 1
temp=${1%.*}.HEAD^1.$$.${1#*.}
fullpath=`git ls-tree --name-only --full-name HEAD^ $1`
test ! -z "$1" || exit 2
echo "extracting '$fullpath' from HEAD^..."
git show HEAD^:$fullpath > $temp
vim -fd $1 $temp
echo "cleaning up..."
rm $temp
This can act as a simplified mergetool when you just want to
review changes made to some file.