Added plugin for OS X Time Machine

A set of functions to simplify listing OS X Time Machine backups, and
deleting old ones. Pulled from various script solutions found on Stack
Overflow, adapted to the Bash-it framework.

The functions allow to show which backups can be found on the connected
Time Machine volume. The 'delete' function allows to safely remove all
backups except for the latest one - this can be used to free up space on
the Time Machine volume. The 'delete' function uses functionality of the
OS to safely remove the old backups, no information is lost.

The 'delete' function will only ask for the password once, then keep the credentials.
Source: http://stackoverflow.com/a/30547074/1228454

plugins/available/osx-timemachine.plugin.bash

@@ -0,0 +1,84 @@
+cite about-plugin
+about-plugin 'OS X Time Machine functions'
+
+function time-machine-destination() {
+  group "osx-timemachine"
+  about "Shows the OS X Time Machine destination/mount point"
+
+  echo $(tmutil destinationinfo | grep "Mount Point" | sed -e 's/Mount Point   : \(.*\)/\1/g')
+}
+
+function time-machine-list-machines() {
+  group "osx-timemachine"
+  about "Lists the OS X Time Machine machines on the backup volume"
+
+  local tmdest="$(time-machine-destination)/Backups.backupdb"
+
+  find "$tmdest" -maxdepth 1 -mindepth 1 -type d | grep -v "/\." | while read line ; do
+    echo "$(basename "$line")"
+  done
+}
+
+function time-machine-list-all-backups() {
+  group "osx-timemachine"
+  about "Shows all of the backups for the specified machine"
+  param "1: Machine name (optional)"
+  example "time-machine-list-all-backups my-laptop"
+
+  # Use the local hostname if none provided
+  local COMPUTERNAME=${1:-$(scutil --get ComputerName)}
+  local BACKUP_LOCATION="$(time-machine-destination)/Backups.backupdb/$COMPUTERNAME"
+
+  find "$BACKUP_LOCATION" -maxdepth 1 -mindepth 1 -type d | while read line ; do
+    echo "$line"
+  done
+}
+
+function time-machine-list-old-backups() {
+  group "osx-timemachine"
+  about "Shows all of the backups for the specified machine, except for the most recent backup"
+  param "1: Machine name (optional)"
+  example "time-machine-list-old-backups my-laptop"
+
+  # Use the local hostname if none provided
+  local COMPUTERNAME=${1:-$(scutil --get ComputerName)}
+  local BACKUP_LOCATION="$(time-machine-destination)/Backups.backupdb/$COMPUTERNAME"
+
+  # List all but the most recent one
+  find "$BACKUP_LOCATION" -maxdepth 1 -mindepth 1 -type d -name 2\* | sed \$d | while read line ; do
+    echo "$line"
+  done
+}
+
+# Taken from here: http://stackoverflow.com/a/30547074/1228454
+function _tm_startsudo() {
+    sudo -v
+    ( while true; do sudo -v; sleep 50; done; ) &
+    SUDO_PID="$!"
+    trap _tm_stopsudo SIGINT SIGTERM
+}
+function _tm_stopsudo() {
+    kill "$SUDO_PID"
+    trap - SIGINT SIGTERM
+    sudo -k
+}
+
+function time-machine-delete-old-backups() {
+  group "osx-timemachine"
+  about "Deletes all of the backups for the specified machine, with the exception of the most recent one"
+  param "1: Machine name (optional)"
+  example "time-machine-delete-old-backups my-laptop"
+
+  # Use the local hostname if none provided
+  local COMPUTERNAME=${1:-$(scutil --get ComputerName)}
+
+  # Ask for sudo credentials only once
+  _tm_startsudo
+
+  echo "$(time-machine-list-old-backups "$COMPUTERNAME")" | while read i ; do
+    # Delete the backup
+    sudo tmutil delete "$i"
+  done
+
+  _tm_stopsudo
+}