You'll have to read in the file once for each column, or store the information and go through the data structure later.
I was originally thinking in terms of arrays of arrays, but I don't want to get into References.
I'm going to make the assumption that each line is the same length. Makes it simpler that way. We can use split to split your line into individual letters:
my = $line = "ABC"
my @split_line = split //, $line;
This will give us:
$split_line[0] = "A";
$split_line[1] = "B";
$split_line[2] = "C";
What if we now took each letter, and placed it into a @vertical_array
.
my @vertical_array;
for my $index ( 0..@#split_line ) {
$vertical_array[$index] .= "$split_line[$index];
}
Now let's do this with the next line:
$line = "123";
@split_line = split //, $line;
for my $index ( 0..@#split_line ) {
$vertical_array[$index] .= "$split_line[$index];
}
This will give us:
$vertical_array[0] = "A1";
$vertical_array[1] = "B2";
$vertical_array[2] = "C3";
As you can see, I'm building the $vertical_array with each interation:
use strict;
use warnings;
use autodie;
use feature qw(say);
my @vertical_array;
while ( my $line = <DATA> ) {
chomp $line;
my @split_line = split //, $line;
for my $index ( 0..$#split_line ) {
$vertical_array[$index] .= $split_line[$index];
}
}
#
# Print out your vertical lines
#
for my $line ( @vertical_array ) {
say $line;
}
__DATA__
ABC
123
XYZ
BOY
FOO
BAR
This prints out:
A1XBFB
B2YOOA
C3ZYOR
If I had used references, I could probably have built an array of arrays and then flipped it. That's probably more efficient, but more complex. However, that may be better at handling lines of different lengths.