Re: Determining hash order for sorting array

Honestly, though a hash's order may remain unchanged from one call to keys to the next, any design that relies on any notion of hash order is probably in need of a change, unless you're planning on using a tied hash with a well-defined behavior with regard to hash order.

What are you actually trying to do, by the way? Sometimes if you can sort of describe the task at hand, a better solution (better than relying on hash element orders) will turn up in the ensuing discussion.

Dave

Comment on Re: Determining hash order for sorting array

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Re^2: Determining hash order for sorting array by PenguinPwrdBox (Initiate) on Aug 21, 2005 at 16:14 UTC
Here is essentially what I am doing... I have been charged with the task of unifying all local login information for about 300 Unix machines. This means UID's, GID's, etc... What I have done, is created a perl script, that will harvest all the lines in /etc/passwd (this will be adapted for shadow and group as well - it's only a matter of changing the source to the file handle) - and then map them using a key=>value pair of the username=>line_in_passwd. I then use a simple while loop to parse each value, split it into the actual data (sans :), and use a DBI call to place it into a MySQL DB, along with the current working hostname. I have also populated an array with the usernames, the idea being that if a key matches an entry in the array, the DB already contains the info for that user/host pair, and it should branch to then check the values of that user, to ensure nothing has changed. As of now, it does not branch, I have been simply playing with the logic to ensure that if the statement is true, it will. Here is a snippet of that logic block. Please excuse the syntax...for I am nowhere near as effective yet as I would like to be :) `CHILD:while( (my $key, my $value) = each %passwd){ for(@existing_users){next CHILD if /$key/;} $value =~ /\w:(.):(\d):(\d):(.):(.):(.*)/; my $query = "INSERT INTO passwd (username, pwd_loc, uid, gid, +gecos, home_dir, shell, hostname) values('$key', '$1', '$2', '$3', '$ +4', '$5', '$6', '$hostname')"; my $sth = $dbh->prepare($query); $sth->execute() \|\| die("Couldn't exec sth!"); }` [download] The `next CHILD if` statement will be replaced with a subroutine to check for differences if I can get this right. My thought, regarding the hash order, was to see if there may be a better way to scan that hash for an existing user entry in the DB. And just by the way - I know that you Monks are huge advocates of using .pm's. There may indeed be one out there that I could adapt for this, however, being as new as I am to both Perl, and programming in general, it's in my best interest to reinvent the wheel :) Thanks again for the help Monks.	[reply] [d/l] [select]
Re^3: Determining hash order for sorting array by punch_card_don (Curate) on Aug 21, 2005 at 16:24 UTC
there may be a better way to scan that hash for an existing user entry in the DB Indeed - instead of storing your identified usernames in an array (list), create a hash of existing user names. Then you can do: `if ($existing_users{$key} ) { ...do some stuff... }` [download] Where, instead of pushing the user names retrieved from your db onto a @existing_users array, you would have populated a %existing_users hash with 1's using the user id's as the keys Forget that fear of gravity, Get a little savagery in your life.	[reply] [d/l]
Re^4: Determining hash order for sorting array by PenguinPwrdBox (Initiate) on Aug 21, 2005 at 16:50 UTC
That worked perfectly. Thank you very much.	[reply]