calculate the difference between 2 dates

gistfile1.txt

#!/bin/bash
## calculate the difference between 2 dates

date2stamp () {
    date --utc --date "$1" +%s
}

dateDiff (){
    case $1 in
        -s)   sec=1;      shift;;
        -m)   sec=60;     shift;;
        -h)   sec=3600;   shift;;
        -d)   sec=86400;  shift;;
        *)    sec=86400;;
    esac
    dte1=$(date2stamp $1)
    dte2=$(date2stamp $2)
    diffSec=$((dte2-dte1))
    if ((diffSec < 0)); then abs=-1; else abs=1; fi
    echo $((diffSec/sec*abs))
}

## usage
# -s in sec. | -m in min. | -h in hours  | -d in days (default)
#   dateDiff -s "2006-10-01" "2006-10-31"
#   dateDiff -m "2006-10-01" "2006-10-31"
#   dateDiff -h "2006-10-01" "2006-10-31"
#   dateDiff -d "2006-10-01" "2006-10-31"
#   dateDiff "2006-10-01" "2006-10-31"