snapreport

#!/bin/bash

function format_data ()
{
    local amount="$1"
    local suffixes=(" " "K" "M" "G" "T" "P" "E" "Z" "Y")
    local testnum="$amount"
    local divisor="1"
    local suffix=""
    #bash arithmetic uses 64bit, so use bc
    for ((index = 0; index < ${#suffixes[@]}; ++index))
    do
        suffix="${suffixes[$index]}"
        testnum=`echo "$amount/($divisor)" | bc`
        if ((testnum < 1000))
        then
            break
        fi
        divisor="$divisor*1024"
    done
    local prespace="  "
    if ((testnum >= 100))
    then
        prespace=""
    else
        if ((testnum >= 10))
        then
            prespace=" "
        fi
    fi
    if [[ "$divisor" == "1" ]]
    then
        #don't use bc for non-fractional cases
        local displaydata="$amount   "
    else
        local displaydata=`echo "scale = 2; $amount/($divisor)" | bc -l`
        #we switch at 1000, not 1024, so check for having no digit before decimal point
        if [[ "$displaydata" == .* ]]
        then
            #because leading zero behavor is unspecified in bc
            displaydata=0"$displaydata"
        fi
    fi
    echo "$prespace$displaydata$suffix"
}

if (($# < 1))
then
    echo "usage: $0 <filesystem>@<snapshot>"
    exit 1
fi
if [[ "$1" != ?*@* || "$1" == /* ]]
then
    echo "Input must be a snapshot with filesystem name"
    echo "usage: $0 <filesystem>@<snapshot>"
    exit 1
fi
filesystem=`echo "$1" | cut -f1 -d@`
mysnap=`echo "$1" | cut -f2- -d@`
allsnaps=`zfs list -Hd 1 -t snapshot -o name "$filesystem" | cut -f2- -d@`
position=`echo "$allsnaps" | grep -n "^$mysnap\$" | cut -f1 -d:`
if [[ $position == "" ]]
then
    echo "snapshot not found"
    exit 1
fi
latersnaps=`echo "$allsnaps" | tail -n +$((position + 1))`

#unique
if ((position > 1))
then
    prevsnap=`echo "$allsnaps" | tail -n +$((position - 1)) | head -n 1`
    #we have, and must account for, previous snapshots
    remaining[0]=`zfs get -Hp written@"$prevsnap" "$filesystem"@"$mysnap" | awk '{print $3}'`
else
    #no previous snapshot, the referenced property provides the number we want (ie, assume a "previous snapshot" of zero usage)
    remaining[0]=`zfs get -Hp referenced "$filesystem"@"$mysnap" | awk '{print $3}'`
fi
names[0]="unique"

#other snaps
index=1
for snap in $latersnaps
do
    if ((position > 1))
    then
        prevwritten=`zfs get -Hp written@"$prevsnap" "$filesystem"@"$snap" | awk '{print $3}'`
    else
        prevwritten=`zfs get -Hp referenced "$filesystem"@"$snap" | awk '{print $3}'`
    fi
    snapwritten=`zfs get -Hp written@"$mysnap" "$filesystem"@"$snap" | awk '{print $3}'`
    remaining[index]=$((prevwritten - snapwritten))
    names[index]="$snap"
    index=$((index + 1))
done

#data not yet snapshotted
if ((position > 1))
then
    prevwritten=`zfs get -Hp written@"$prevsnap" "$filesystem" | awk '{print $3}'`
else
    prevwritten=`zfs get -Hp referenced "$filesystem" | awk '{print $3}'`
fi
curwritten=`zfs get -Hp written@"$mysnap" "$filesystem" | awk '{print $3}'`
remaining[index]=$((prevwritten - curwritten))
#allow the display loop to report the "active" line, rather than as a special case
remaining[index + 1]=0
names[index]="active"
end=$index

echo "  SIZE    ENDING SNAPSHOT"
for ((index = 0; index <= end; ++index))
do
    amount=$((remaining[index] - remaining[index + 1]))
    if ((amount != 0))
    then
        echo "$(format_data $amount)   ${names[$index]}"
    fi
done