Diff for "BashFAQ/102"

Differences between revisions 2 and 3

How to get the difference between two dates

It's best if you work with timestamps throughout your code, and then only convert timestamps to human-readable formats for output. If you must handle human-readable dates as input, then you will need something that can parse them.

Using GNU date, for example:

# get the seconds passed since Jan 1, 2010 (localtime)
then=$(date -d "2010-01-01 00:00:00" +%s)
now=$(date +%s)
echo $(($now - $then))

To print a duration as a human-readable value you'll have to do some math:

# some constants
minute_secs=60 hour_secs=$((60 * minute_secs)) day_secs=$((24 * hour_secs))
# get total
seconds_since=$(($now - $then))
# parse
days=$((seconds_since / day_secs))
hours=$((seconds_since % day_secs / hour_secs))
minutes=$((seconds_since % day_secs % hour_secs / minute_secs))
seconds=$((seconds_since % day_secs % hour_secs % minute_secs))
# pretty-print
echo "$days days, $hours hours, $minutes minutes and $seconds seconds."

Or, without the verbose labels:

# Bash/ksh
((duration = now - then))
((days = duration / 86400))
((duration %= 86400))
((hours = duration / 3600))
((duration %= 3600))
((minutes = duration / 60))
((seconds = duration % 60))
echo "$days days, $hours hours, $minutes minutes and $seconds seconds."

To convert the timestamp back to a human-readable date, using recent GNU date:

date -d "@$now"

(See FAQ #70 for more about converting Unix timestamps into human-readable dates.)

CategoryShell

-  ⇤ ← Revision 2 as of 2010-01-06 14:04:45 → 
  Size: 1165
  Editor: GreyCat
  Comment: clarify
+   ← Revision 3 as of 2010-07-30 13:46:05 → ⇥
  Size: 1590
  Editor: GreyCat
  Comment:
-Deletions are marked like this.
+Additions are marked like this.
 Line 3:
-Using GNU `date`, first parse the dates into timestamps and work on those:
+It's best if you work with timestamps throughout your code, and then only convert timestamps to human-readable formats for output.  If you must handle human-readable dates as input, then you will need something that can parse them.

Using GNU `date`, for example:
-Line 6:
+Line 8:
-# get the seconds passed since 2010 (localtime)
echo $(($(date +%s) - $(date -d "2010-01-01 00:00:00" +%s)))
+# get the seconds passed since Jan 1, 2010 (localtime)
then=$(date -d "2010-01-01 00:00:00" +%s)
now=$(date +%s)
echo $(($now - $then))
-Line 10:
+Line 14:
-To print that as a human-readable value you'll have to do some math:
+To print a duration as a human-readable value you'll have to do some math:
-Line 16:
+Line 20:
-seconds_since=$(($(date +%s) - $(date -d "2010-01-01 00:00:00" +%s)))
+seconds_since=$(($now - $then))
-Line 26:
+Line 30:
-To parse the timestamp back to a readable date, using GNU `date`:
+Or, without the verbose labels:
{{{
# Bash/ksh
((duration = now - then))
((days = duration / 86400))
((duration %= 86400))
((hours = duration / 3600))
((duration %= 3600))
((minutes = duration / 60))
((seconds = duration % 60))
echo "$days days, $hours hours, $minutes minutes and $seconds seconds."
}}}

To convert the timestamp back to a human-readable date, using recent GNU `date`:
-Line 29:
+Line 46:
-# get a date that is 90 days into the future (recent GNU date)
date -d "@$(($(date +%s) + 60 * 60 * 24 * 90))"
+date -d "@$now"