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Re: Comparing two files

by lyklev (Pilgrim)
on Oct 04, 2006 at 20:08 UTC ( #576397=note: print w/replies, xml ) Need Help??

in reply to Comparing two files

Your program has a couple of problems:

First, you are splitting on comma's, then the pc no (the first field) has index 0, index 1 gets you the ip-address.

Next, you are reading the entire second file for each line found in the first file, that will give you some serious I/O for big files.

Perl is not very good at finding out whether something is in a list. If you want to do that, think of a hash in stead. Lists are for processing bulk data element by element. Keeping this in mind, let's rewrite the program.

Assuming you have two files, pcs_old.csv and pcs_new.csv, starting with the opening stuff:

use strict; use warnings; open (OLD, "<pcs_old.csv"); open (NEW, "<pcs_new.csv"); my %old; # where pc numbers will get stored...
Read the old file line by line...
while (<OLD>) { chomp; my @fields = split /,/; my $pc = $fields[0]; # get the first field $pc =~ s/"//g; # get rid of the quotes $old {$pc} = 1; # make an entry in the hash }
Now do the same for the new pc file, but instead of storing them, see if an entry exists in the database with old pc's:
while (<OLD>) { chomp; my @fields = split /,/; my $pc = $fields[0]; # get the first field $pc =~ s/"//g; # get rid of the quotes if (! exists $old {$pc}) { # the new pc file has a pc which did not exist # in the old pc file print "new PC found: $pc\n"; } } # and cleanup close (OLD); close (NEW);

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