Perl simple filehandling of text - perl

Question

What this program is meant to do is that it reads a text file which looks like:
Item \t\t Price
apple \t\t 20
orange \t\t 50
lime \t\t 30
I'm using split function to split these 2 columns and then i should apply a -25% discount on all items and print it out to a new file. My code so far does what i want but the new text file has a '0' value under my last number in price column. I also get 2 errors if i run it with "use warnings" which are:
Use of uninitialized value $item in multiplication * ...
Use of uninitialized value $item[0] in concatenation (.) ...
I should also tell total number of items calculated but i get like 5 1's instead of 5. (11111 instead of 5)
use strict;
use warnings;
my $filename = 'shop.txt';
if (-e $filename){
open (IN, $filename);
}
else{
die "Can't open input file for reading: $!";
}
open (OUT,">","discount.txt") or die "Can't open output file for writing: $!";
my $header = <IN>;
print OUT $header;
while (<IN>) {
chomp;
my #items = split(/\t\t/);
foreach my $item ($items[1]){
my $discount = $item * (0.75);
print OUT "$items[0]\t\t$discount\n";
}
}

Answer 1

This is too complicated and not clear what are you doing in foreach loop and you are not skipping empty lines. Keep it simple:
use warnings;
use strict;
use v5.10;
<>; # skip header
while(my $line = <>)
{
chomp $line;
next unless ($line);
my ($title, $price ) = split /\s+/, $line;
if( $title && defined $price )
{
$price *= 0.75;
say "$title\t\t$price";
}
}
and run like
perl script.pl <input.txt >output.txt

Answer 2

use strict;
use warnings;
my $filename = 'shop.txt';
if (-e $filename){
open (IN, $filename);
}
else{
die "Can't open input file for reading: $!";
}
open (OUT,">","discount.txt") or die "Can't open output file for writing: $!";
my $header = <IN>;
my $item;
my $price;
print OUT $header;
while (<IN>) {
chomp;
($item, $price) = split(/\t\t/);
my $discount = $price*0.75;
print OUT "$item $discount\n";
}
This should help! :)

Answer 3

If the total item count isn't very important to you:
$ perl -wane '$F[1] *= 0.75 if $. > 1; print join("\t", #F), "\n";' input.txt
Output:
Item Price
apple 15
orange 37.5
lime 22.5
If you really need the total item count:
$ perl -we 'while (<>) { #F = split; if ($. > 1) { $F[1] *= 0.75; $i++ } print join("\t", #F), "\n"; } print "$i items\n";' input.txt
Output:
Item Price
apple 15
orange 37.5
lime 22.5
3 items

Answer 4

I'd use this approach
#!/usr/bin/perl
use strict;
use warnings;
my %items;
my $filename = 'shop.txt';
my $discount = 'discount.txt';
open my $in, '<', $filename or die "Failed to open file! : $!\n";
open my $out, ">", $discount or die "Can't open output file for writing: $!";
print $out "Item\t\tPrice\n";
my $cnt = 0;
while (my $line = <$in>) {
chomp $line;
if (my ($item,$price) = $line =~ /(\w.+)\s+([0-9.]+)/){
$price = $price * (0.75);
print $out "$item\t\t$price\n";
$items{$item} = $price;
$cnt++;
}
}
close($in);
close($out);
my $total = keys %items;
print "Total items - $total \n";
print "Total items - $cnt\n";
Using regex capture groups to capture the item and price (using \w.+ in case the item is 2 words like apple sauce), this will also prevent empty lines from printing to file.
I also hard coded the Item and Price header, probably a good idea if you are going to be using a consistent header.
Hope it helps
---Update ----
I added 2 examples of a total count in my script. The first one is using a hash and printing out the hash size, the second method is using a counter. The hash option is good except if your list has 2 items that are the same in which case the key of the hash will be overridden with the last item found which shares the same name. The counter is a simple solution.