AWS EC2 CLI Volume Snapshot

#!/bin/bash

VOL_ID=$1
DESCRIPTION=$2
MAX_BACKUPS=$3

ERROR_EMAIL=test@developer.com
LOG_FILE=~/aws_vol_backup.log

function log {
        LOG_LINE="`date`: volume($VOL_ID): $1"
        echo "$LOG_LINE"
        echo "$LOG_LINE" >> $LOG_FILE
}

function print_usage {
        ME=`basename $0`
        echo "Usage: $ME <volume-id> [ <snapshot description>, <max number of backups> ]" 
        echo "Arguments:"
        echo -e "\tvolume-id: The AWS EBS volume-id"
        echo -e "\tsnapshot description: The description to attach to the snapshot"
        echo -e "\tmax number of backups: Only retain up to this many backups"
}

log "Starting backup script called with arguments: $1 $2 $3"

if [ "$VOL_ID" = "" ]; then
        >&2 echo "You must pass the volume id to snapshot"
        print_usage
        exit 1
fi

if [ "$DESCRIPTION" = "" ]; then
        DESCRIPTION="Snapshot for volume with id $VOL_ID"
fi

if [ "$MAX_BACKUPS" = "" ]; then
        MAX_BACKUPS=8
fi

PENDING_SNAPSHOTS=`aws ec2 describe-snapshots --filters Name=volume-id,Values=$VOL_ID Name=status,Values=pending`

if [ "$PENDING_SNAPSHOTS" = "" ]; then
        log "No pending snapshots, creating new snapshot with description $DESCRIPTION"
        aws ec2 create-snapshot --volume-id $VOL_ID  --description "$DESCRIPTION"
        #Now clean up the old snapshots
        CMD="aws ec2 describe-snapshots --filters Name=volume-id,Values="$VOL_ID" | 
awk --field-separator '\t' ""'"'{ strp=substr($7,0,length($7)-1); "date -d \""strp"\" +\"%s\"" | getline result; print $6 " " $7 " " result; }'"'"' | 
sort -r -k 3 | 
awk '"'"'{ if (a>'$MAX_BACKUPS') { cmd="aws ec2 delete-snapshot --snapshot-id="$1; print cmd; system(cmd); } else { ++a; print "Retaining " $1 " " $2; } }'"'"' -'
        log "Retaining up to $MAX_BACKUPS snapshots..."
        eval $CMD
else
        log "Skipping creation; snapshot is pending: $PENDING_SNAPSHOTS"
fi

log "Completed backup script"