Question

I am trying to pull 1 week data from sql server, then trying to write the data into files with separate names.
Following codes does not work, and I cannot find a way to create file handlers with a variable.

Another question is that if the size of sql data is huge (1-2 gigabyte per day, and the entire table is over 1 year period), then is this monthly fetching method is faster than daily fetching?

    my $sqlGetEid = "select trunc(datetime, 'DD') truncdate, x, y from z
        where DATETIME between TO_DATE('$dt1','YYYY-MM-DD') and TO_DATE('$dt1','YYYY-MM-DD')+7";

    for ($day=1; $day<=7; $day++){
        open('dayfile_$day', "> ./temp/Wireless_$day.csv");  
    }

    while ( my ($tday,$x,$y) = $curSqlEid->fetchrow_array() ) 
    {
        printf {'dayfile_$tday'} ("%s,%d\n", $x,$y);
    }

    for ($day=1; $day<=7; $day++){
        close('dayfile_$day');  
    }

Answer 1

You can’t use plain strings as variables like you’re trying to do.

The simplest way I can think of for this is to use a hash to map file names with filehandles.

Here’s an example of how you could do that:

use strict;
use warnings;

my %files;

foreach my $i (1..7) {
    my $fh;
    open($fh, '>', "day_$i.log") || die "Ooups: $i: $!";
    $files{$i} = $fh;
}

foreach my $i (1..7) {
    my $fh = $files{$i};
    print $fh "hello $i\n";
}

foreach my $i (1..7) {
    my $fh = $files{$i};
    close $fh;
}