# Git filtering


Excellent [idea
Ton](http://tonkersten.com/archives/2009/08/10/my_git_hash_filter/index.html)!

How to make a custom filter in `git` to expand the string `$Hash$` to 
something more usefull, ala the `$Id$` (which `git` already supports), but
then with more info (committer, date, etc.).

Which also helped in this case was the 
[Pro Git book](http://progit.org/book/ch7-2.html) which is, as of now, a
must buy.

But as always is the case between Ton and me, I find his scripts too
long :-) So I *miekified* his solution.

First we need two scripts, one to expand $Hash$ and another one
to collapse it again:

`git.expand`:

    #!/bin/sh
    id=$(git show -s --pretty=format:%h\ %ci\ ${SUDO_USER:-${LOGNAME}}%n)
    sed -e 's!\([[:space:]]*\$[H]ash\)\$!\1: '"${id} "'\$!'

and `git.collapse`:

    #!/bin/sh
    sed -e 's!\([[:space:]]*\$[H]ash\):.*\$!\1\$!'

And a final check to see if they are working:

     % echo '$Hash$' | git.expand
     $Hash: 8c84acf 2009-08-11 19:28:20 +0200 miekg $

Looking nice.

    % echo '$Hash$' | git.expand | git.collapse
    $Hash$

Wonderful - the scripts work. Now we need to set up the filtering
in `git`.

# Filtering
As Ton also explained you need to add the filtering commands
to your global `~/.gitconfig` and then edit a `.gitattributes` to
enable this on a per repository basis.

In `~/.gitconfig` add:

    [filter "hash"]
	smudge = git.expand
	clean = git.collapse

And in your `.gitattributes` add:

    *   filter=hash

See gitattributes(5) for more information on this.

# Test
Now run a little test:

    % echo '$Hash$' > h
    % git add h
    % git commit -m'testadd' -- h
    Created commit b5189fd: testadd
     1 files changed, 1 insertions(+), 0 deletions(-)
     create mode 100644 h

And, and... and...:

    % cat h
    $Hash$

Huh, unexpanded? Well yes, you need to remove and checkout the file
for it all to work:

    % rm h && git checkout -- h && cat h
    $Hash: b5189fd 2009-08-11 19:50:19 +0200 miekg $

# Putting it all together
So now I only need a little wrapper around `vi` and `git` to do 
all this automatically. So here is `vit2`:

CODE(sh){
#!/bin/zsh
# (c) Copyright Miek Gieben, 2009 Licensed under GPL v3
# expands $[H]ash$ to $[H]ash: short_hash date committer $
# with the help of git filter
zparseopts -D -K -- m:=o_msg	# -m mesg is supported
[[ $? != 0 ]] && exit 1
o_msg="$o_msg[2]"

for file in "$@"; do
    dir="$(dirname "$file")"
    cd "$dir" 2>/dev/null || continue
    base="$(basename "$file")"
    chmod +w "$base" 2>/dev/null

    if ${EDITOR:-/usr/bin/vi} "$base"; then
	[[ ! -e "$base" ]] && exit 0	# nothing saved
	git add "$base"
	if [[ -z "$o_msg" ]]; then
	    git commit -- "$base"
	else
	    git commit -m "$o_msg" -- "$base"
	fi
	rm "$base"  && git checkout -- "$base"
    fi

    chmod a-w "$base" 2>/dev/null
    cd - >/dev/null
done
}CODE

That's all folks! 

And thanks [Ton](http://www.tonkersten.com).