Iteratively convert Perforce repository to git -- preserves existing git commit hashes.

iteratively-convert-perforce-repository-to-git.sh

#!/bin/bash -evx

PERFORCE_DEPOT_PATH=$1
GIT_REPOSITORY_URL=$2

git_project_name=$(echo ${GIT_REPOSITORY_URL} | sed -e 's|^.*/||' -e 's|\.git||')

rm -rf ${git_project_name}
git clone ${GIT_REPOSITORY_URL}

(
  cd ${git_project_name}
  git update-ref refs/remotes/p4/master $(git log --format='%H' | head -n 1)
  git symbolic-ref refs/remotes/p4/HEAD refs/remotes/p4/master
  git p4 sync ${PERFORCE_DEPOT_PATH} || true
  git p4 rebase
  git push
)

See https://gist.github.com/noel-yap/2d084b543cfab0782edc for a version of this script that handles the initial import as well.