Time difference of 14 digit date YYYYmmDDHHMMSS - unix

Question

I need a Unix script which i can find the time difference between 2 times look like YYYYmmDDHHMMSS
Example
T1=20120624192555
T2=20120624204006
So the time difference will be =1:14:11
Any clue?

Answer 1

I'm not sure if you can get around specifying the date format, but here is a rather lengthy date solution:
# Get seconds since epoch
D1=$(date --date "${T1:0:4}-${T1:4:2}-${T1:6:2} ${T1:8:2}:${T1:10:2}: ${T1:12:2}" +%s)
D2=$(date --date "${T2:0:4}-${T2:4:2}-${T2:6:2} ${T2:8:2}:${T2:10:2}: ${T2:12:2}" +%s)
date --date "0 + $(( D2 - D1 )) seconds" +%T
See here for the ${VAR:OFF:LEN} reference.
Note: as mentioned by jrouquie below, this fails when exceeding 24 hours. This is a limitation of the date command, $(( D2 - D1 )) still gives the correct result in seconds though.

Answer 2

time1=`echo $1 | sed -r 's/([0-9]{4})([0-9]{2})([0-9]{2})([0-9]{2})([0-9]{2})([0-9]{2})/\1-\2-\3 \4:\5:\6/'`
time2=`echo $2 | sed -r 's/([0-9]{4})([0-9]{2})([0-9]{2})([0-9]{2})([0-9]{2})([0-9]{2})/\1-\2-\3 \4:\5:\6/'`
seconds1=`date --utc -d "$time1" +%s`
seconds2=`date --utc -d "$time2" +%s`
difference=`expr $seconds2 - $seconds1`
echo `expr $difference / 3600`:`expr "(" $difference / 60 ")" % 60`:`expr $difference % 60`
Note the use of --utc which prevents a bug with daylight saving time.
Caveats:
This script does not check input.
It assumes $2 > $1.
It could be rewritten to factor repeated code
EDIT: regarding the first comment, here is a version without the "-r" option to sed (-r means --regexp-extended, which here allowed to dispense with all the backslashes).
time1=`echo $1 | sed 's/\([0-9]\{4\}\)\([0-9]\{2\}\)\([0-9]\{2\}\)\([0-9]\{2\}\)\([0-9]\{2\}\)\([0-9]\{2\}\)/\1-\2-\3 \4:\5:\6/'`
time2=`echo $2 | sed 's/\([0-9]\{4\}\)\([0-9]\{2\}\)\([0-9]\{2\}\)\([0-9]\{2\}\)\([0-9]\{2\}\)\([0-9]\{2\}\)/\1-\2-\3 \4:\5:\6/'`
seconds1=`date --utc -d "$time1" +%s`
seconds2=`date --utc -d "$time2" +%s`
difference=`expr $seconds2 - $seconds1`
echo `expr $difference / 3600`:`expr "(" $difference / 60 ")" % 60`:`expr $difference % 60`

Answer 3

Here is a solution taking the best of the one by Thor/kjp and mine:
#!/bin/bash
function seconds_since_epoch() {
echo $(date --utc --date "${1:0:4}-${1:4:2}-${1:6:2}
${1:8:2}:${1:10:2}:${1:12:2}" +%s)
}
difference=$(( `seconds_since_epoch $2` - `seconds_since_epoch $1` ))
echo \
`expr $difference / 3600`:\
`expr "(" $difference / 60 ")" % 60`:\
`expr $difference % 60`