Bash script to backup home directories using rsync

backup_home.sh

#!/usr/bin/env bash

# Script to backup the home directory to an external hardrive mounted at /media/backup
# Uses rsync, dpkg, and mail (for error logging)

SRC='/home/*'
DEST='/media/backup'
RSYNC_OPTS='-haAXuv --delete'
EXCLUDE='*/.cache/* */.thumbnails/* */.config/google-* lost+found .gvfs'
EXCLUDE="$(echo $EXCLUDE | sed 's/\(\S\+\)/ --exclude \1/g')"
LOGFILE='/home/mehta/logs/backup'
TMPFILE='/tmp/backup_out'
ERRFILE='/tmp/backup_err'
ERRFLAG='ERROR'
EMAIL='devm33@gmail.com' 

# clear out tmp files
[ -a $TMPFILE ] && rm -rf $TMPFILE
[ -a $ERRFILE ] && rm -rf $ERRFILE
touch $TMPFILE
touch $ERRFILE

# check if interactive
if [[ -t 0 || -p /dev/stdin ]];
then
    INTERACTIVE=1
    echo "note: rsync progress can be followed at $TMPFILE"
else
    INTERACTIVE=0
fi

# log handling for this script
function log {
    # if passed params appends them to log file
    # otherwise appends TMPFILE to log file
    if [ $# -gt 0 ];
    then
        LOG="$@"
    else
        LOG="$(cat $TMPFILE)"
    fi
    echo -e "$LOG" >> $LOGFILE
    # also duplicates output to stdout if INTERACTIVE
    if [ $INTERACTIVE ];
    then
        echo -e "$LOG"
    fi
}

# error handling for this script
function error_out {
    # if passed args use those as error message
    # otherwise assumes error message will be in ERRFILE
    if [ $# -gt 0 ];
    then
        ERRMSG="$@"
    else
        ERRMSG="$(cat $ERRFILE)"
    fi
    ERRMSG="There was an error backing up files on ganesh on $(date):\n${ERRMSG}"
    echo -e "$ERRMSG" | mail -s "Backup Error" $EMAIL
    log "$ERRMSG"
    echo "$ERRFLAG" >> $LOGFILE # leave a flag for next time
    exit 1
}

# check if destination is a mount point otherwise quit
(mount | grep -q $DEST ) || error_out "Backup destination not mounted" 

# keep an updated list of all installed packages
dpkg --get-selections | grep -v deinstall | cut -f 1 > $DEST/packages

# backup everything in /home with a few exceptions
rsync $RSYNC_OPTS $EXCLUDE $SRC $DEST > $TMPFILE 2> $ERRFILE || error_out

# send an email if last time there was an error
if [ "$ERRFLAG" == "$(tail -n 1 $LOGFILE)" ];
then
    echo "Backup successfully restarted on $(date)" | mail -s "Backup Success" $EMAIL
fi

# log success
log "$(tail -n 2 $TMPFILE)" # this is the summary from the end of rsync verbose output
log "Home directories backed up successfully on $(date)"