Why after the while loop I am only getting last row value?

Question

This is the files I am reading,

#Log1
Time    Src_id  Des_id  Address
0   34  56  x9870
2   36  58  x9872
4   38  60  x9874
6   40  62  x9876
8   42  64  x9878
         


        

Answer 1

Following code demonstrates how to read and print log files (OP does not specify why he splits lines into fields)

use strict;
use warnings;
use feature 'say';

my $fname1  = 'log1.txt';
my $fname2  = 'log2.txt';
my $div     = "\t";

my $file1   = read_file($fname1);
my $file2   = read_file($fname2);

print_file($file1,$div);
print_file($file2,$div);

sub read_file {
    my $fname = shift;
    
    my @data;
    
    open my $fh, '<', $fname
        or die "Couldn't read $fname";
        
    while( <$fh> ) {
        chomp;
        next if /^#Log/;
        push @data, [split];
    }
        
    close $fh;
    
    return \@data;
}

sub print_file {
    my $data = shift;
    my $div  = shift;
    
    say join($div,@{$_}) for @{$data};
}

Output

Time    Src_id  Des_id  Address
0       34      56      x9870
2       36      58      x9872
4       38      60      x9874
6       40      62      x9876
8       42      64      x9878
Time    Src_id  Des_id  Address
1       35      57      x9871
3       37      59      x9873
5       39      61      x9875
7       41      63      x9877
9       43      65      x9879

Let's assume that OP wants to merge two files into one with sorted lines on Time field

• read files into %data hash with Time field as key
• print header (@fields)
• print hash values sorted on Time key

use strict;
use warnings;
use feature 'say';

my(@fields,%data);

my $fname1  = 'log1.txt';
my $fname2  = 'log2.txt';

read_data($fname1);
read_data($fname2);

say join("\t",@fields);
say join("\t",@{$data{$_}}) for sort { $a <=> $b } keys %data;

sub read_data {
    my $fname = shift;
    
    open my $fh, '<', $fname
        or die "Couldn't open $fname";
        
    while( <$fh> ) {
        next if /^#Log/;
        if( /^Time/ ) {
            @fields = split;
        } else {
            my @line = split;
            $data{$line[0]} = \@line;
        }
    }
        
    close $fh;
}

Output

Time    Src_id  Des_id  Address
0       34      56      x9870
1       35      57      x9871
2       36      58      x9872
3       37      59      x9873
4       38      60      x9874
5       39      61      x9875
6       40      62      x9876
7       41      63      x9877
8       42      64      x9878
9       43      65      x9879