packetstormer has asked for the wisdom of the Perl Monks concerning the following question:

Hello

I am having a strange problem writing to a file with Tie::File. The code is below. The output to screen writes fine but the actual file isn't change. Its not permissions as I can write to the file fine if I don't split the line. I wonder if there is a fundamental problem with splitting the tie array and editing an element in that? 

#!/usr/bin/perl

use strict;
use CGI;
use Tie::File;

my $query = new CGI;
#my $file = $query->param('filename');
my $file = '/tmp/test.csv';
my @lines;
print $query->header();

tie @lines, 'Tie::File', $file or die "No file found to work with.";

print "We got $#lines lines in this file";
foreach my $i(@lines) {
        my @tmp = split (",",$i);
        if($tmp[6] eq "6 Elm") {$tmp[6] = 'XXXXX'}
        print "$i\n";

        }

untie @lines;

[download]

Does anything look obvious?

Replies are listed 'Best First'.
Re: Tie::File Write Problem
by toolic (Bishop) on Nov 17, 2011 at 19:30 UTC
    After you tied the file to the @lines array, you never make a modification to the @lines array. See Tie::File. 
    tie @lines, 'Tie::File', $file or die "No file found to work with.";
$lines[0] = 'foo';  # this should change the tied file

    [download]
[reply]
[d/l]
      That's my confusion, doesn't this line change the element in the line? 
       if($tmp[6] eq "6 Elm") {$tmp[6] = 'XXXXX'}

      [download]
      I am splitting each line up based on the commas in the line and changing that element
[reply]
[d/l]
        That line does not change the @lines array or the tied file. That just changes the @tmp array. Tip #4 from Basic debugging checklist: 
        use Data::Dumper;
print Dumper(\@tmp);
print Dumper(\@lines);

        [download]
[reply]
[d/l]

        @tmp is a completely separate variable that is not tied to the file. The split copies the data. You would have to add the following inside the foreach-loop to change the file as you intented:

        $i= join(',',@tmp);

        [download]

        Note that even this works only because $i actually is an alias to the data in @lines and not a copy (this is magic done by the foreach loop)

[reply]
[d/l]

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