21

I'd like to have a time, say 6:45am, and add an amount of hours, say 1.45 hours, to result in another time. So I'd like to add 1.45 hours to 6:45am to get another time.

Is there a command line utile for that? I've done some Googling, and read the man page for date and haven't found anything like that. wcalc doesn't seem to handle time calculations.

EDIT: Mar 6, 2015. This is the script I ended up with to use decimal hours. It could use some error checking to make sure HH:MM uses 2 digits for the hours.

#!/bin/bash
# Mar 6, 2015
# Add decimal hours to given time. 
# Syntax: timeadd HH:MM HOURS
# There MUST be 2 digits for the hours in HH:MM.
# Times must be in military time. 
# Ex: timeadd 05:51 4.51
# Ex: timeadd 14:12 2.05
echo " "
# If we have less than 2 parameters, show instructions and exit.
if [ $# -lt 2 ]
then
    echo "Usage: timeadd HH:MM DECHOURS"
    exit 1
fi
intime=$1
inhours=$2
# Below is arithmetic expansion $(())
# The bc calculator is standard on Ubuntu. 
# Below rounds to the minute. 
inminutes=$(echo "scale=0; ((($inhours * 60)*10)+5)/10" | bc)
echo "inminutes=$inminutes"
now=$(date -d "$intime today + $inminutes minutes" +'%H:%M')
echo "New time is $now"
Bulrush
  • 772

1 Answers1

33

Command line:

$ now=$(date -d "06:45 today + 105 minutes" +'%H:%M')
$ echo "$now"
08:30

$now will hold the time you specified.

You can put a lot of things in between the " and "; like the current time and add 105 to it. 

$now=$(date -d "06:45 today + 2.5 hour" +'%H:%M')
date: invalid date `06:45 today + 2.5 hour'
$now=$(date -d "06:45 today + 2:30 hour" +'%H:%M')
date: invalid date `06:45 today + 2:30 hour'
$ now=$(date -d "06:45 today + 2 hour" +'%H:%M')
$ echo "$now"
08:45

No decimals allowed...

From comments: To get the answer for 1.45 decimal hours:

$ now=$(date -d "06:45 today + $((145 * 60 / 100)) minutes" +'%H:%M')
$ echo "$now:
8:12
Krista K
  • 343
Rinzwind
  • 299,756
  • Squeee! Thank you! I had trouble reading the last part, but the part around the %H:%M are two single quotes. Is there any way to do this in decimal hours instead of converting it to minutes? That would eliminate a step. I'd even be open to installing a special calculator. I do appreciate your work though, please don't misunderstand. – Bulrush Dec 24 '14 at 13:36
  • "+10 days" works too. So does "+2 hour". Of course you could also add a method here to make minutes from 2.5 hours ;) I never found a full list of words you can use... – Rinzwind Dec 24 '14 at 14:38
  • @Bulrush hmm no decimals allowed with hour :D – Rinzwind Dec 24 '14 at 14:50
  • @Rinzwind I'm not sure but did you try 2:30 hour instead of 2.5 hour? – αғsнιη Dec 24 '14 at 15:02
  • @KasiyA see the edit :D – Rinzwind Dec 24 '14 at 15:03
  • 1
    @Rinzwind So one possible is using 2 hour + 30 minutes ;) – αғsнιη Dec 24 '14 at 15:07
  • You could simulate fractional (decimal) hours using shell arithmetic e.g. for 1.45hr use date -d "06:45 today + $((145 * 60 / 100)) minutes" +'%H:%M' – steeldriver Dec 24 '14 at 16:58
  • @steeldriver almost. That ends up with 8:12 ... – Rinzwind Dec 24 '14 at 17:07
  • Erm... 0.45 of an hour is 27 minutes surely? The OP appears to be asking specifically about decimal fractions. – steeldriver Dec 24 '14 at 17:09
  • hmm damn ehm :D here have some upvotes @steeldriver ;) – Rinzwind Dec 24 '14 at 17:22