Show differences between two Time Machine backups

Below is a quick Bash script to display the difference between two Time Machine backups.

The output is simply the pathnames of the files that were added to Time Machine in that time period. This may of course be piped to another command/script to provide further info - say, the amount of space used.

Cheat: Provide a simple date (formatted the same way that Time Machine does) instead of the "older" backup pathname, and it'll work whether or not there was a backup then. (The order of the arguments is unimportant; the script will figure it out.)

#!/bin/bash

LF=$'\n'
usage="Usage: $(basename $0) Time-Machine-folder-1 Time-Machine-folder-2"
usage=$usage$LF"(Compare the two Time Machine backup folders;"
usage=$usage"find and display files that were backed up in that time period.)"

function tweakDate { # to a fmt understood by find cmd
   echo "$1" | awk -v FS="" '{print $1$2$3$4$5$6$7$8$9$10" "$12$13":"$14$15":"$16$17}'
}

if [ ! $# == 2 ] ; then
{
   echo "$0 requires two arguments; the Time Machine folders to compare." >&2
   echo "$usage" >&2
   exit 1
}
fi

baseName1=$(basename $1)
baseName2=$(basename $2)

# NB: operator must be escaped or will signify redirection
if [ "$baseName1" \< "$baseName2" ] ; then
{
   olderFldr=$1
   recentFldr=$2
   olderFldrName=$baseName1
   recentFldrName=$baseName2
}
else
{
   reverse=TRUE
   olderFldr=$2
   recentFldr=$1
   olderFldrName=$baseName2
   recentFldrName=$baseName1
}
fi

if [ ! -d "$olderFldr" ] ; then
{
   echo -n "Warning: $olderFldr doesn't seem to exist;" >&2
   echo " maybe you're just using it to specify a date?..." >&2
}
fi

olderFldrParent=$(dirname $olderFldr)
recentFldrParent=$(dirname $recentFldr)

if [ ! $olderFldrParent == $recentFldrParent ] ; then
{
   echo -n "Warning: These folders are not in the same parent folder;" >&2
   echo " this may not be what you want..." >&2
}
fi

olderFldrDate=$(tweakDate $olderFldrName)
recentFldrDate=$(tweakDate $recentFldrName)

if [ ! -d "$recentFldr" ] ; then
{
   latestBackup="${recentFldrParent}/$(ls -1 $recentFldrParent | tail -2 | head -1)"

   echo "Can't find $recentFldr; searching the latest backup" >&2
   echo "    ($latestBackup)" >&2
   echo "    for files modified between $olderFldrDate and $recentFldrDate." >&2
   echo "    This may take awhile..." >&2
   echo $LF >&2

   find -x "$latestBackup" -type f -newermt "$olderFldrDate" \! -newermt "$recentFldrDate" -print
}
else
{
   echo "Now searching for backups in $recentFldrName" >&2
   echo "    that are more recent than $olderFldrDate." >&2
   echo "    This may take awhile..." >&2
   echo $LF >&2

   find -x "$recentFldr" -type f -newermt "$olderFldrDate" -print
}
fi

# eof