datediff.sh

#! /bin/bash
 
function usage {
    echo 'Subtract two timestamps in ISO 8601 format.'
    echo 'If end timestamp is missing, assume now.'
    echo 'Returns value in seconds.'
    echo ''
    echo 'usage: $0 start [end]'
    echo ''
    exit
}
 
# ISO 8601 format is "yyyy-MM-dd'T'HH:mm:ssZ"
 
function iso8601_to_lbolt {
    u="$(echo $1 | sed -e 's/T/ /' | sed -e 's/-05:00/ EST/')"
    echo $(date -d "$u" +%s )
}
 
if [ $# -lt 1 ] ; then
    usage
fi
 
start=$(iso8601_to_lbolt $1)
 
if [ $# -eq 1 ] ; then
    end=$(date +%s)
else
    end=$(iso8601_to_lbolt $2)
fi
 
echo $(($end - $start))