Quite often, I find myself using git for non-work related activity on my work laptop. Yeah, yeah, I know.

Normally, I remember to set my email to be my home address before starting work.

$ mymail='dom [at] happygiraffe (dot) net'
$ git config user.email $mymail

Of course, you’d use your proper email address, instead of that obfuscated form.

Note that we don’t use --global. This change is specific to the repository that we’re working in.

Unfortunately, I usually just dive in and start working. About four or five commits down the line, I realise I’ve screwed up. What then?

git filter-branch to the rescue! We just need to change a couple of environment variables and redo each commit.

$ git filter-branch --env-filter "export GIT_AUTHOR_EMAIL=$mymail GIT_COMMITTER_EMAIL=$mymail" master
Rewrite 0c5299bf98bf30938bb1d0fc0211aa9f3a9ddcf8 (3/3)
Ref 'refs/heads/master' was rewritten

Like all uses of filter-branch, you should only do this on an unpublished repository, as it’s effectively altering history.

There is a reference to the original commits left behind, in case I screwed something up. When you’ve checked that everything looks OK, you can clean up.

$ git for-each-ref --format="%(refname)" refs/original/ | xargs -n 1 git update-ref -d
$ git reflog expire --expire=now --all
$ git gc --prune=now
Counting objects: 9, done.
Delta compression using up to 2 threads.
Compressing objects: 100% (7/7), done.
Writing objects: 100% (9/9), done.
Total 9 (delta 1), reused 0 (delta 0)

Quite often, you want to change a file temporarily whilst you work on something, but you know you don’t want to commit it. Right now I want to change my project’s logging from INFO to DEBUG, but I don’t want to commit that.

There’s a command git update-index which has a flag --assume-unchanged. And it just makes those files ignored for a while.

$ git status
# On branch master
# Changed but not updated:
#   (use "git add ..." to update what will be committed)
#   (use "git checkout -- ..." to discard changes in working directory)
#
#	modified:   src/main/webapp/WEB-INF/log4j.xml
#
no changes added to commit (use "git add" and/or "git commit -a")
$ git update-index --assume-unchanged src/main/webapp/WEB-INF/log4j.xml
$ git status
# On branch master
nothing to commit (working directory clean)

Easy! Now, edit away.

… time passes …

And now to get everything back to normal.

$ git update-index --verbose --really-refresh
src/main/webapp/WEB-INF/log4j.xml: needs update
$ git status
# On branch master
# Changed but not updated:
#   (use "git add ..." to update what will be committed)
#   (use "git checkout -- ..." to discard changes in working directory)
#
#	modified:   src/main/webapp/WEB-INF/log4j.xml
#
no changes added to commit (use "git add" and/or "git commit -a")

I have to be honest, this is slightly hacky. It would be nice to be able to tell git “ignore this change,” in the way you can say “add this change”. But it works OK for now.

A colleague was asking:

I’m trying to work out a technique for searching for an occurrence of a phrase in _all_ revisions of a specific file in a subversion repository. How can I do this?

Of course, in subversion, the answer is slow and complicated. But, you can use git (and git svn in particular) to achieve the answer fairly simply (and much more quickly).

First, you just clone the subversion repository into git. This takes a while, mostly because subversion isn’t that quick.

  git clone -s https://svn.example.com/proj

Then, you can wrap a little bit of shell scripting around git to get what you need.

  cd proj
  git branch -a | grep tags/ | while read tag
  do
    git --no-pager grep 'something' $tag -- some/file.txt
  done

So, we pull out a list of tags, and run git grep over each one.

There may well be a more effective way to do this, but hey, it took seconds to come up with. And it shows off the reason I like git — it’s so scriptable.

Just a quick one based on today’s git ready: text-based graph. That describes how to get nice ascii-charts of your git repo. But the command is too long to type. So:

  git config --global alias.tree 'log --graph --pretty=oneline'

Now, I can just do git tree. Lovely.