Re: DB_File problem
- From: "evlong" <evlong@xxxxxxxxx>
- Date: 18 Aug 2005 10:45:18 -0700
Thanks for the help.
John W. Krahn wrote:
> evlong wrote:
> > I am working on a script to base64 encode a file and then scramble the
> > lines but also keep track of the order in which these lines were
> > scrambled. Anyway, the problem occurs when I untie and undef all
> > references to the file. After all references are destroyed, the file
> > that was referenced ends up rewriting itself.
> >
> > So here is a flow of the program:
> > 1.Base64 encode the file passed at the command line.
> > 2.Randomly swap lines in the file and store the pairs (line numbers)
> > that were swapped for later use.
> > 3.Then get rid of all references to the base64 encoded file (This is
> > were the rewrite of the entire file occurs).
> > 4.Then save the pairs that were swapped to a file for use when
> > descrambling the encoded file.
> >
> > This is probably a dumb question but I would appreciate any help I can
> > get.
> >
> > The source follows:
> >
> > #scramble.pl
>
> You should start your programs with the warnings and strict pragmas to
> help you detect mistakes.
>
> use warnings;
> use strict;
>
>
> > #ARGV[0] is the source file
> > #ARGV[1] name of the file that is encoded
> > #ARGV[2] is the order file
> >
> > use MIME::Base64;
> > use DB_File;
> >
> > open(IN, $ARGV[0]);
>
> You should *ALWAYS* verify that the file was opened.
>
> open IN, '<', $ARGV[0] or die "Cannot open $ARGV[0]: $!";
>
>
> > open(OUT, ">".$ARGV[1]);
>
> Yes *ALWAYS*!
>
> open OUT, '>', $ARGV[1] or die "Cannot open $ARGV[1]: $!";
>
>
> > binmode IN;
> > while(read(IN, $buffer, 4104)){
>
> Even though you are requesting to read 4104 bytes that does not mean
> that $buffer will contain exactly 4104 bytes so if it makes a difference
> you should check for this.
>
>
> > print OUT encode_base64($buffer);
> > }
> > close(OUT);
> > close(IN);
> >
> >
> > $db = tie @data, "DB_File", $ARGV[1], O_RDWR, 777, $DB_RECNO;
>
> It looks like your problem is that you are setting the file mode to
> read-only.
>
> $ ls -l TEST
> /bin/ls: TEST: No such file or directory
> $ perl -le'use DB_File;tie @data,"DB_File","TEST",O_RDWR,777,$DB_RECNO;'
> $ ls -l TEST
> -r----x--t 1 john users 0 2005-08-18 02:47 TEST
>
> You should be using the octal number 0777 instead of the decimal number
> 777 (although why you would need execute permissions on a text file?)
>
> Also you should *ALWAYS* verify that the file opened.
>
> my $db = tie my @data, 'DB_File', $ARGV[1], O_RDWR, 0777, $DB_RECNO
> or die "Cannot open $ARGV[1]: $!";
>
> Also it might be easier to use the Tie::File module for this.
>
>
> > $length = $db->length;
> >
> > srand;
> > for($i=0; $i<$length; $i++){
> > $index1 = $i;
> > $index2 = int(rand($length-1));
>
> $length is the number of elements in the array so by subtracting one
> that means that the last line in the file will never be accessed by $index2.
>
>
> > $db->get($index1, $tmp1);
> > $db->get($index2, $tmp2);
> > $db->put($index1, $tmp2);
> > $db->put($index2, $tmp1);
> > $order .= $index1.",".$index2."\n";
> > }
> > undef $db;
>
> It shouldn't be necessary to "undef $db" as the following untie destroys
> all references.
>
>
> > untie @data;
> > open(ORDER, ">".$ARGV[2]);
>
> You should *ALWAYS* verify that the file was opened.
>
> open ORDER, '>', $ARGV[2] or die "Cannot open $ARGV[2]: $!";
>
>
> > print ORDER $order;
> > close (ORDER);
> >
> > exit;
>
>
> John
> --
> use Perl;
> program
> fulfillment
.
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- From: evlong
- Re: DB_File problem
- From: John W. Krahn
- DB_File problem
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