Parsing time stamps and calculating difference

Question

So I am parsing a log file and look for certain time stamps and then subtracting them to get time elapsed.

So I tried a simple code to see if I can use Time::Piece but wasnt successful. My code below:

use Time::Piece;

my ($S, $E);

GetOptions (
    "S=s" => \$S,
    "E=s" => \$E,
    );

my $start    = $S;
my $end = $E;
my %build_time;

my $start_time;
my $end_time;
if(my ($start_time) = $start =~ /\[gg\s+(\d+\:\d+\:\d+)\s+I\]/){
    print"Build_Time: start at $start_time\n";
}
#--------------------
# End time from dj
if(my ($end_time) = $end =~ /\[gg\s+(\d+\:\d+\:\d+)\s+I\]/){
    print "Build_Time: end at $end_time\n";
}

my $difference = Time::Piece->strptime($end_time,'%H:%M:%S') - Time::Piece->strptime($start_time,'%H:%M:%S');

print " difference: $difference \n";

Execute: perl time.pl -S "[gg 8:11:03 I]: Copyright" -E "[gg 8:19:03 I]: BT_DEPTH=99 "

Build_Time: start at 8:11:03 Build_Time: end at 8:19:03 difference: 0

Also what is the time is in 24 hr format and log contains over night run ( so the difference would be negative)?

Answer 1

Your code has a scoping issue: $start_time and $end_time in your if statements mask the outer variables. If the time difference is 23:59:59 max you can use a modulo operation to fix the negative seconds output caused by crossing a date boundary:

time.pl:

use strict;
use warnings;
use Getopt::Long;

use Time::Piece;
my ($S, $E);

GetOptions (
    "S=s" => \$S,
    "E=s" => \$E,
    );

my $start    = $S;
my $end = $E;
my %build_time;

my $start_time;
my $end_time;
if( ($start_time) = $start =~ /\[gg\s+(\d+\:\d+\:\d+)\s+I\]/){
    print"Build_Time: start at $start_time\n";
}
#--------------------
# End time from dj
if( ($end_time) = $end =~ /\[gg\s+(\d+\:\d+\:\d+)\s+I\]/){
    print "Build_Time: end at $end_time\n";
}

my $tp_st = Time::Piece->strptime($start_time,'%H:%M:%S');
my $tp_e =  Time::Piece->strptime($end_time,'%H:%M:%S');

my $difference = $tp_e -$tp_st;
$difference %= 60*60*24; # 1 day
print " difference: $difference \n";

testing:

perl time.pl -S "[gg 8:19:04 I]: Copyright" -E "[gg 8:19:14 I]: BT_DEPTH=99 "
Build_Time: start at 8:19:04
Build_Time: end at 8:19:14
 difference: 10 


perl time.pl -S "[gg 8:19:04 I]: Copyright" -E "[gg 8:19:03 I]: BT_DEPTH=99 "
Build_Time: start at 8:19:04
Build_Time: end at 8:19:03
 difference: 86399 

Answer 2

If input is indeed limited to times within 24 hours then if start time is larger than end time it means it rolled into another day. So you can substract Time::Piece objects and adjust if negative

use warnings;
use strict;
use feature 'say';

use Getopt::Long;
use Time::Piece;

GetOptions ( "S=s" => \my $S, "E=s" => \my $E );

my ($tp_beg, $tp_end) = map { 
    my ($time) = /\[gg\s+ ([0-9]+:[0-9]+:[0-9]+) \s+ I\]/x;
    die "Unexpected input format ($_)" if not $time;
    Time::Piece->strptime($time, "%H:%M:%S")
} $S, $E;

my $diff_secs = $tp_end - $tp_beg;
$diff_secs += 24*60*60  if $diff_secs < 0;

say "Difference is $diff_secs secs";

say "Difference is ", sec_in_day_to_hms($diff_secs);

sub sec_in_day_to_hms {  # add ($tt >= 3600*24) branch for multiple days
    my ($tt) = @_;
    my $msg = do {
        if ( $tt >= 3600 ) {
            sprintf("%d:%02d:%02d (hr:min:sec)",
                $tt/3600, ($tt%3600)/60, $tt%60);
        }
        elsif ( $tt >= 60 ) {
            sprintf("%d min %d sec", ($tt%3600)/60, $tt%60);
        } 
        else { sprintf("%d sec", $tt%60); }
    };
    return $msg;
}

Running as in the question

perl time_diff.pl -S "[gg 8:11:03 I]: Copyright" -E "[gg 8:19:03 I]: BT_DEPTH=99 "

prints

Difference is 480 secs
Difference is 8 min 0 sec

If we change 8:19:03 to 6:19:03 (so it rolled all the way by about two hours short of a full day) and run it as

perl time_diff.pl -S "[gg 8:11:03 I]: Copyright" -E "[gg 6:19:03 I]: BT_DEPTH=99 "

then it prints

Difference is 79680 secs
Difference is 22:08:00 (hr:min:sec)

---

A comment on the code in the question

It firstly has a mistake of defining a variable $start_time also inside an if block

if(my ($start_time) = $start =~ /.../){

and that variable masks (shadows) the one with the same name declared earlier. After the if block is exited, the earlier $start_time is restored, um, to undef.

When that's used later in the program (for subtraction) it would print warnings -- if you had them on! Please add

use strict;
use warnings;

to the top of every program. These are directly helpful.

One simple way to fix that would be to just remove that my -- then the regex's return is assigned indeed to the earlier declared $start_time. However, I find that there are too many variables introduced for the purpose so I'd suggest to simplify instead.

Then, the possibly negative difference isn't handled, what the question itself asserts.