Tool in UNIX to subtract dates

Question

Is there any tool in Solaris UNIX (so no GNU tool available) to subtract dates? I know that in Linux we have gawk that can subtract one date from another. But in Solaris the maximum we have is nawk (improved awk) which cannot perform date calculations. Also I cannot use perl... :(

Is there anyway to do dates calculations like 20100909-20001010 ?

UPDATE: Is bc able to perform dates calculations?

Thanks guys

Answer 1

Here is an awk script I just wrote up, should work with an POSIX awk. You'll have to try the Solaris version; remember that there are two versions of Awk on Solaris as well, one in /bin and one in /usr/xpg4/bin/awk (which is nawk, I believe).

BEGIN {
    daysofmonth["01"] = 0; daysofmonth["02"] = 31; daysofmonth["03"] = 59;
    daysofmonth["04"] = 90; daysofmonth["05"] = 120; daysofmonth["06"] = 151;
    daysofmonth["07"] = 181; daysofmonth["08"] = 212; daysofmonth["09"] = 243;
    daysofmonth["10"] = 273; daysofmonth["11"] = 304; daysofmonth["12"] = 334;
    fullday = 86400;
}
/[12][09][0-9][0-9][01][0-9][0123][0-9]/ {
    year = substr($0, 1, 4); month = substr($0, 5, 2); day = substr($0, 7, 2);
    date = ((year - 1970) * 365.25) + daysofmonth[month] + day - 1;
    if ((year % 4) == 0 && month > 2) { date = date + 1; }
    print date * fullday - (25200);
}
{}

Pass a YYYYmmdd date string through and it will be converted to number of seconds since the Epoch (with a bit of give for being on day boundaries). Then you will be able to subtract the two.

today=`echo 20110210 | awk -f convdate.awk`
then=`echo 20001231 | awk -f convdate.awk`
sincethen=`expr $today - $then`

Answer 2

Unfortunately, none of the POSIX command line utilities provide arithmetic on dates. date -d and date +%s are the way to go if you have them, but they're GNU extensions.

There's a clumsy hack with touch that sort of works for checking that a date is at least n days in the past:

touch -t 201009090000 stamp
if [ -n "$(find stamp -mtime +42)" ]; then ...

(Note that this code may be off by one if DST started or stopped in the interval and the script runs before 1am.)

Several people have ended up implementing date manipulation libraries in Bourne or POSIX shell. There are a few examples and links in the comp.unix.shell FAQ.

Installing GNU tools may be the way of least pain.

Answer 3

I would try using the date command which is part of POSIX so it is just about everywhere. UPDATE: Unfortunately, it seems that -d is not part of POSIX date and likely not there on Solaris. Thus this likely won't answer the OPs question.

d1=`date -d 20100909 +%s`
d2=`date -d 20001010 +%s`

Now d1 and d2 are integers that correspond to seconds since the unix epoch. Thus to get the difference between the two, we subtract( $((d1-d2)) in bash) and covert to whatever units we want. Days are the easiest:

echo "$(((d1-d2)/86400)) days"

How to do the conversion will likely be different if you don't have bash. The most portable way may be to use expr (expr's posix man page).

Answer 4

If you have Python:

from time import *
date1 = strptime("20100909","%Y%m%d")
date2 = strptime("20001010","%Y%m%d")
diff = mktime(date1) - mktime(date2)
print repr(d/86400) + " days"

You tagged your question "gawk" but you say "no GNU tools". Gawk has date arithmetic.

Answer 5

Perl is likely to be installed, and it's easy enough to grap modules from CPAN, install them in your home directory, and refer to them in your program. In this case, the Date::Calc module has a Delta_Days subroutine that will help.

Answer 6

Wrt GNU date on Solaris:

I say this again:

Too many Solaris SysAdmins take pride in deliberately not installing the official packages from Sun (now Oracle) that make a Solaris system "GNU compatible" when they configure a new host. Beats me why.

GNU Date is excellent and should be available by default on any Solaris host, IMHO.

On Solaris 10

Install package SFWcoreu from the Solaris Companion CD. After install you will find GNU date in /opt/sfw/bin/date

On Solaris 11

You may already have it as I believe it is part of the standard install. It is however called gdate in order to distinguish it from the Sun version of date.

Do this if not installed:

pkg install //solaris/file/gnu-coreutils

Answer 7

python:

 from datetime import datetime as dt
 a = dt(2010, 9, 9)
 b = dt(2000, 10, 10)
 print (a - b).days

Answer 8

For the record, dateutils is my attempt at providing a set of portable tools that cover date arithmetics. Your example boils down to

ddiff -i '%Y%m%d' 20001010 20100909
=>
  3621

The -i specifies the input format.

Answer 9

Install some tools!

I mean, it is Solaris, what do you expect? ;)