Calculate time difference in Unix shell script

[Melvin Thong]

Hello,

I have a question on shell scripting. I have a scenario whereby an application has captured the start timestamp on a file in the format of
2002-11-14 09:31 when the application services started up.

I am required to produce a script to calculate the time difference between the current system date with the timestamp captured on the file I have mentioned above. The checking is scheduled to run every 4 hours.

I am wondering is there a way that I can do a conversion of the time captured on file into a value where I can do the mathematical expression such as subtraction.

My objective is to subtract the current system date with the timestamp that was captured on the file.

time_difference=curr_date - prev_timestamp

How can this be done if I were to use the shell script to calculate the time difference. Appreciate if you could give me some advice on how to get this done. Thank you.

Regards,
Melvin

[harry d brown jr]

I suggest you read this link for Clay's script (caljd.sh):

http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0xea948cc5e03fd6118fff0090279cd0f9,00.html

Plus have a look here for a lot of scripts:
http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0x026250011d20d6118ff40090279cd0f9,00.html


live free or die
harry

[john korterman · Accepted solution]

Hi Melvin,
there is probably no easy way of doing that. I was once requested to do something similar and I ended up making the attached script. It is slow but can return the number of seconds elapsed since midnight, Jan 1 of a specified year, e.g. 1970 and a certain specified date.
Example:

# ./return_seconds.sh 1970 2002 11 14 9 31 00
# 1037266260

The attached script can - if executed without parameters - also calculate the number of seconds elapsed since midnight Jan 1 1970 and current system time, e.g.:
# ./return_seconds.sh
1039595802

Difference:
# echo 1039596799 - 1037266260 | bc
2330539


However, if you do not expect the time difference to be bigger than a few days you can speed up things by only counting back to midnight of e.g. the current year, e.g.:
# date
Ons. 11 Dec. 2002 08:45

# ./return_seconds.sh 2002 2002 Dec 11 8 45 00
29753100

./return_seconds.sh 2002 2002 11 14 9 31 00
27423060

# echo 29753100 - 27423060 | bc
2330040

As time is passing the two results are not identical...
Hope it is of some use, but if you wait long enough I am sure someone will come up with a perl one-liner!

regards,
John K.

[Christian Gebhardt]

Hi

the same question:
http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0x31d5cdec06f1d61190050090279cd0f9,00.html

Chris

[Jean-Louis Phelix]

hi,

Simple C program (compile with make) then use within a shell script like :

#!/usr/bin/sh
# get date in VAR for example :
VAR=$(cat file | line | cut -c1-2)
# use my prog (each field from date is an arg)
myprog $(echo $VAR | tr ':-' ' ')

Regards.

[F. X. de Montgolfier]

Hi,

I am not aware of a shell command that would make this easy; but if you look at
http://docs.hp.com/cgi-bin/onlinedocs.py?mpn=B2355-90683&service=hpux&path=../B2355-90683/00/00/89&title=HP-UX%20Reference%20Volume%204%3A%20Section%203

you'll find how to use difftime() to get the time difference between two dates...

Cheers,

FiX

[Robin Wakefield]

Hi Melvin,

Quick bit of perl would also do it:

perl -e '{use Time::Local;($y,$mo,$d,$h,$mi)=split /:| |-/,shift;print time-timelocal(0,$mi,$h,$d,$mo-1,$y-1900),"\n";}' "2002-12-11 11:22"

Rgds, Robin.