script:Taskwarrior auto sync script, with the ability to sync in background (non-blocking) and with delays so that it waits for you to finish modifing all files. In additions, it allows you to perform task undo (because once you have synced, you cannot undo). Requires tmux or screen for some form of background session.

on-exit-sync.sh

#!/bin/bash
# This hooks script syncs task warrior to the configured task server.
# The on-exit event is triggered once, after all processing is complete.

# let's do a quick check. If the taskw command already is synchronize, we
# wouldn't need to run this script:)
for arg in $*; do
  if [[ "$arg" == api:* ]]; then
    IFS=':'
    read -ra api_level <<< "$arg"
    api_level=${api_level[1]}
    case $api_level in
      1|2) ;;
      *) echo "SyncOnExit: Unspoorted api level '$api_level'"
         exit ;;
     esac
  fi
  if [[ "$arg" == command:synchronize ]]; then
    exit
  fi
done

TMUX_SESSION_TOKEN="_taskw-sync"
SYNC_DELAY=30
TASKW_HOOK_TMP_DIR="$HOME/.task/hooks/.tmp"
TASKW_IS_DIRTY_FILE="$TASKW_HOOK_TMP_DIR/sync_is_dirty"

mkdir -p "$TASKW_HOOK_TMP_DIR"

# The logic is as following:
# 1. only continue the script if something was modified in this session,
#    or something in previous session has not been synced.
# 2. spawn a tmux session to run in background (non-blocking)
# 3. within the session, sleep to create delays, allow user to *undo*
#    or add more data.
# 4. when that happens, and when this script is called again, kill
#    the previous existing session, and the new session will starts
#    from 1. again.
# 5  if it succeed, it will empty the is_dirty file.
# 6. if it fails, the taskw will remained to be dirty and will tries
#    to perform sync the next time.

# Count the number of tasks modified
n=0
while read modified_task
do
    n=$(($n + 1))
done

# if file exists and it's non-empty
is_dirty=$(test -e "$TASKW_IS_DIRTY_FILE" && cat $TASKW_IS_DIRTY_FILE)

if [[ $is_dirty || (($n > 0)) ]]; then
    # kill existing session, if exists
    tmux kill-session -t "$TMUX_SESSION_TOKEN" 2>/dev/null && echo "Existing taskw-sync has been stopped."
    # mark taskw sync as dirty
    echo 1 > "$TASKW_IS_DIRTY_FILE"

    # SYNC IN BACKGROUND.
    # tmux also prevent duplicated session
    tmux new -d -s "$TMUX_SESSION_TOKEN" 'sleep '"$SYNC_DELAY"' \
      && task sync >> ~/.task/sync_hook.log 2>&1 \
      && notify-send Taskwarrior "Successfully synced." \
      && true > '"$TASKW_IS_DIRTY_FILE"' \
      || notify-send Taskwarrior "Failed to sync."'
    echo "Taskw will be synced in $SYNC_DELAY seconds."
fi

exit 0