Dynamic Array Inside a Foreach Loop

Question

First time poster and new to Perl so I'm a little stuck. I'm iterating through a collection of long file names with columns separated by variable amounts of whitespace for example:

0     19933     12/18/2013 18:00:12  filename1.someextention
1     11912     12/17/2013 18:00:12  filename2.someextention
2     19236     12/16/2013 18:00:12  filename3.someextention

These are generated by multiple servers so I am iterating through multiple collections. That mechanism is simple enough.

I'm focused solely on the date column and need to ensure the date is changing like the above example as that ensures the file is being created on a daily basis and only once. If the file is created more than once per day I need to do something like send an email to myself and move on to the next server collection. If the date changes from the first file to the second exit the loop as well.

My issue is I don't know how to keep the date element of the first file stored so that I can compare it to the next file's date going through the loop. I thought about keeping the element stored in an array inside the loop until the current collection is finished and then move onto the next collection but I don't know the correct way of doing so. Any help would be greatly appreciated. Also, if there is a more eloquent way please enlighten me since I am willing to learn and not just wanting someone to write my script for me.

@file = `command -h server -secFilePath $secFilePath analyzer -archive -list`;
@array = reverse(@file); # The output from the above command lists the oldest file first 

    foreach $item (@array) {
    @first = split (/ +/, @item);
    @firstvar = @first[2];
#if there is a way to save the first date in the @firstvar array and keep it until the date
 changes       
    if @firstvar == @first[2] { # This part isnt designed correctly I know.                }
            elsif @firstvar ne @first[2]; {
            last;
            }
}

rutter · Accepted Answer · 2013-12-19 01:57:55Z

3

One common technique is to use a hash, which is a data structure mapping key-value pairs. If you key by date, you can check if a given date has been encountered before.

If a date hasn't been encountered, it has no key in the hash.

If a date has been encountered, we insert 1 under that key to mark it.

my %dates;
foreach my $line (@array) {
    my ($idx, $id, $date, $time, $filename) = split(/\s+/, $line);

    if ($dates{$date}) {
        #handle duplicate
    } else {
        $dates{$date} = 1;

        #...
        #code here will be executed only if the entry's date is unique
    }

    #...
    #code here will be executed for each entry
}

Note that this will check each date against each other date. If for some reason you only want to check if two adjacent dates match, you could just cache the last $date and check against that.

In comments, OP mentioned they might rather perform that second check I mentioned. It's similar. Might look like this:

#we declare the variable OUTSIDE of the loop
#if needs to be, so that it stays in scope between runs
my $last_date;
foreach my $line (@array) {
    my ($idx, $id, $date, $time, $filename) = split(/\s+/, $line);

    if ($date eq $last_date) { #we use 'eq' for string comparison
        #handle duplicate
    } else {
        $last_date = $date;

        #...
        #code here will be executed only if the entry's date is unique
    }

    #...
    #code here will be executed for each entry
}

edited Dec 19, 2013 at 1:57

answered Dec 18, 2013 at 23:12

rutter

11.5k1 gold badge32 silver badges47 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Capitalismczar Over a year ago

I think your note is more along the lines of what I need to do....I need to cache the first date reference so I can compare it to the second date reference from the next record in the array. How could I do that?

Capitalismczar Over a year ago

It won't work since I don't even get the date extracted from the filename until after I split the line up into the array. I'm not working with an actual date but a text output of the date...know what I mean?

Capitalismczar Over a year ago

I get it....I knew it would be something simple...you have to run through the first record in the array to record it's date and then keep the date in the hash and when you run the second date through compare the two. I understand.....thanks for the help.

Collectives™ on Stack Overflow

Dynamic Array Inside a Foreach Loop

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related