Git: maintaining many topic branches on a frequently-moving base

Pretty much the same question was asked on the git mailing list: Rebasing Multiple branches at once... The linked response has a perl script attached that generates the commands you would need.

If you want this script to be fast and avoid having it tread on your toes, also consider using git-new-workdir to set up a working copy just for automatic rebasing.

If you find yourself resolving the same conflicts over and over, consider enabling git rerere.

Having said all that, here is an alternate recipe:

# Construct a placeholder commit that has all topics as parent.
HEADS="$(git for-each-ref refs/heads/\*)" &&
MAGIC_COMMIT=$(echo "Magic Octopus"$'\n\n'"$HEADS" |
  git commit-tree \
    $(git merge-base $(echo "$HEADS" | sed 's/ .*//' ))^{tree} \
    $(echo "$HEADS" | sed 's/ .*//;s/^/-p /')) &&
git update-ref refs/hidden/all $MAGIC_COMMIT

# Rebase the whole lot at once.
git rebase --preserve-merges master refs/hidden/all

# Resolve conflicts and all that jazz.

# Update topic refs from the rebased placeholder.
PARENT=
echo "$HEADS" |
while read HASH TYPE REF
do
  let ++PARENT
  git update-ref -m 'Mass rebase' "$REF" refs/hidden/all^$PARENT "$HASH"
done