How to find difference between two timestamps up to milliseconds?

Question

I am new to shell scripting. The heart of my script is to find the difference between two timestamps up to milliseconds. With me I have a file with content of timestamps only as

2012-09-13 15:00:29,290 2012-09-13 15:00:29,297
2012-09-13 15:00:29,428 2012-09-13 15:00:29,447

Like this I have around 30k records, where I should not face any performance issue when I execute script. Many factors like leap year, months with 31 days etc come into picture when I am trying to write script for this.

Can anyone help me on this please?

Answer 1

No need to do complex parsing, date will do all the magic for you, with the help of his friend, bash :

#!/bin/bash
while read d1_1 d1_2 d2_1 d2_2; do
  secdiff=$((
    $(date -d "$d2_1 $d2_2" +%s) - $(date -d "$d1_1 $d1_2" +%s)
  ))
  nanosecdiff=$((
    $(date -d "$d2_1 $d2_2" +%N) - $(date -d "$d1_1 $d1_2" +%N)
  ))
  printf "%s %s - %s %s = %d milliseconds\n" $d2_1 $d2_2 $d1_1 $d1_2 $((
    (secdiff * 1000) + (nanosecdiff / 1000)
  ))
done < YOUR_FILE.txt

OUTPUT

2012-09-13 15:00:29,297 - 2012-09-13 15:00:29,290 = 7000 milliseconds
2012-09-13 15:00:29,447 - 2012-09-13 15:00:29,428 = 19000 milliseconds

See man date

NOTE

• date -d is very useful, it convert timestamps
• %s is the epoch time (seconds since 01-01-1970)
• %N is nanoseconds
• $(( )) and (( )) is for bash arithmetic, see http://mywiki.wooledge.org/ArithmeticExpression
• $( ) stands for command substitution

Is this fit your needs as well ?

Answer 2

A scripting language such as Perl, Python or Ruby will be fast and require little effort. For example, with Perl and Date::Parse:

perl -MDate::Parse -l -ne 's/,/./g; split; print str2time("$_[2] $_[3]") - str2time("$_[0] $_[1]")'

(For each line, replace , by ., split the line into words $_[0] through $_[3], parse the dates formed by the first two and next two words, and print the difference.)