Compare date stored as a string - regex

Question

I have 2 dates (along with date and time)written such that they are in the following formats:
Mon Aug 12 17:32:39 PDT 2013
This is my local time and the other time is stored in the hash. I need to compare this time with that of hash stored time using all the possible comparisions of date as well as time.
This is what I have got
#!/usr/bin/perl
use DateTime;
open(FH,'log.txt');
my %stat;
my ($qbsid, $exittime, $exittimeval);
while ($line = <FH>) {
if ($line =~ /Exit time/) {
($exittime, $exittimeval) = split(': ',$line);
$stat{$qbsid} = {
time => $exittimeval
};
}
}
my $local_time = localtime time;
foreach my $qbsid (keys %stat){
my $cmd = $stat{$qbsid}->{time};
my $cmp = DateTime->compare($cmd,$datetime);
print "$cmp\n";
}
Please suggest me a way to do it.
The hash prints date in the same format as above:
Mon Aug 10 14:31:49 PDT 2013
Thank you for your time.

Answer 1

You should take a look at Date::Calc. That module provides utilities for comparing dates. Regex is the wrong approach here.

Answer 2

I'm going to recommend Time::Piece. This doesn't seem to be too many people's favorite time module, but it comes with Perl which means you don't have to install it. I suspect it will become the standard time module and you might as well learn how to use it. Earlier versions of Time::Piece had issues with Julian dates, but the latest version solved that (and will be in the next Perl release).
Without knowing what your log looks like, and what you are trying to do, it's a bit difficult to help you with your coding. For example, you have a hash of a hash using $qbsid which isn't being set. You need to use use strict; and use warnings; in your program. This would have caught this error. It would have also caught the bug with you declaring $local_time in before your second loop, but using $datetime in that loop.
Also, split does not take a string, but a regular expression pattern as the first argument.
You also need to do a chomp $line right after your while statement. Otherwise, your $line will end with an invisible NL character that will probably cause all sorts of issues.
Now, what exactly are you trying to store? It looks like your inner hash is stored as the current time as the key and your $exittimeval as the value.
I would use the epoch time (which is the number of seconds since January 1, 1970) as the key, and a Time::Piece object as your data:
($exittime, $exittimeval) = split /:\s+/, $line);
my $exit_time_obj = Time::Piece->strptime( $exittimeval, "%a %b %d %H:%M:%S %Z %Y");
my $time_obj = Time::Piece->new(time);
$stat{$qbsid} = {$time_obj->epoch => $exit_time_obj};
Now, you can do your comparisons by changing the key into a Time::Piece object and doing what ever comparisons you want.
By the way, another issue: time keeps a changin'! If you're keying your sub-hash by time, it will be different by the time you get to your second loop. You need to use a second loop to get those actual keys.
my $local_time = Time::Piece->new(time);
foreach my $qbsid (keys %stat) {
for my $key_time ( keys %{ $stat{$qbsid} } )(
my $cmd = $stat{$qbsid}->{$key_time}; # Already a Time::Piece object
if ( $local_time->year eq $cmd->year ) {
print "Years match: " . $cmd->year . "\n";
}
if ( $local_time->month eq $cmd->month ) {
print "Months match: " . $cmd->Month . "\n";
}
...
}
}
Unfortunately, this is very incomplete because I have no idea what you really want to do.
What does your log.txt look like?
What are the different fields in log.txt?
What are you trying to do with `log.txt?
What do you want as a result of your program?
It is impossible for me to know how to guide you.