Distributed file version management in 15 minutes of Bash

You don’t always need to have all the tools at your disposal, but you may want to have some way of checking in your file edits. CVS is too powerful and has a lot of unnecessary parts, while not being distributed. You may not need to keep everything in deltas.

So why not just write them to a directory, without designating a particular root, just keeping track of what was the previously checked out file? (You might want to write a function for checking out an earlier revision, so as to not hide the undo; more below.)

(Edit: rather than the while loop and the shift command, the below could have used the for keyword without the in list.)

#!/usr/bin/env bash

set -euo pipefail

function myhash {
  cksum --raw "$1" | basenc --base32 | tr -d '='
}

while [ $# -gt 0 ]
do
  cd "`dirname "$1"`" || exit 1
  mkdir -p .versioning
  hash="`myhash "$1"`"
  version=.versioning/"$1~$hash"
  cur=""
  if [ -e .versioning/"$1~cur" ]
  then
    if [ "`stat --printf="%s" .versioning/"$1~cur"`" -ne 8 ]
    then
      >&2 echo ".versioning/$1~cur" bad
      exit 1
    fi
    cur="`cat .versioning/"$1~cur"`"
    if [ "$cur" != "$hash" ]
    then
      curfile=.versioning/"$1~$cur"
      if [ ! -e "$curfile" ]
      then
        >&2 echo "$1~$cur" not found;
        exit 1
      fi
      if [ "$cur" != "`myhash "$curfile"`" ]
      then
        >&2 echo "$1~$cur" doesnt hash
        exit 1
      fi
    chmod a-wx "$curfile" || >&2 echo "Could not a-wx orig $curfile"
    ln -s .versioning/"$1~$cur" "$version"'%prev'
    fi
  fi
  echo "$hash" > .versioning/"$1~cur"
  cp --reflink=auto "$1" "$version" 2>/dev/null ||
  [ -e "$version" ] && [ "$hash" = "`myhash "$version"`" ] 
  chmod a-wx "$version" || >&2 echo "Could not a-wx $version"
  shift
done

The result, in the .versioning/ directory relative to versioning.bash being edited:

-rw-r--r-- 1    8  versioning.bash~cur
-r--r--r-- 1 1097  versioning.bash~FYUNFIY
lrwxrwxrwx 1   35  versioning.bash~FYUNFIY%prev -> .versioning/versioning.bash~X7V3TRA
-r--r--r-- 1 1109  versioning.bash~IABNGOY
lrwxrwxrwx 1   35  versioning.bash~IABNGOY%prev -> .versioning/versioning.bash~FYUNFIY
-r--r--r-- 1 1030  versioning.bash~X7V3TRA
lrwxrwxrwx 1   35  versioning.bash~X7V3TRA%prev -> .versioning/versioning.bash~ZQ7C2UQ
-r--r--r-- 1  967  versioning.bash~ZQ7C2UQ
lrwxrwxrwx 1   35  versioning.bash~ZQ7C2UQ%prev -> .versioning/versioning.bash~ZQ7C2UQ

• You may want to make the ~cur file, essentially a HEAD, a symlink, perhaps.
• You may not like the idea of using CRC32. Just switch to another one in cksum, perhaps with truncation.

Checking out an earlier revision and keeping track of that

When checking out an earlier revision, you may want to write its hash (or symlink a revision) into the ~cur file. You may also want to create a %prev symlink going the opposite way just for the act of checkout (it can well express an equivalent of reflog on the same axis, since there is no deltas and chain). So there is more functions to be written — although not like it can’t be performed by hand the first one or two times!