my @qfns;
my @fhs;

for my $qfn (@qfns) {
   open(my $fh, '<', $qfn)
      or die("Can't open \"$qfn\": $!\n");
   push @fhs, $fh;
}

for (;;) {
   my @lines;
   my $all_done  = 1;
   my $some_done = 0;
   for my $fh (@fhs) {
      push @lines, my $line = <$fh>;
      if (defined($line)) { $some_done = 1; }
      else                { $all_done  = 0; }
   }

   exit(0) if $all_done;
   die("Premature eof\n") if $some_done;

   chomp @lines;
   print(join(' ', @lines), "\n");
}
[download]

paste file1 file2 file3 > file.out
[download]

I would open each file and store them in separate arrays where each element of an array is a single line in the corresponding file. Open a fourth file for writing and use a for loop to print each element of each array.

for (my $i = 0; $i < $#file; $i++) {
    print FILE "$file[$i] $file2[$i] $file3[$i]\n";
}
[download]

Or something~

use strict;

open my $FILE1, '<', 'my/input/file1' or die "Could not open FILE1: $!
+";
open my $FILE2, '<', 'my/input/file2' or die "Could not open FILE2: $!
+";
open my $FILE3, '<', 'my/input/file3' or die "Could not open FILE3: $!
+";;

open my $FILE4, '>', 'my/output/file' or die "Could not open FILE4: $!
+";

while (my $file1 = <$FILE1>) {
    my $file2 = <$FILE2>;
    my $file3 = <$FILE3>;
    
    chomp $file1;
    chomp $file2;
    
    print $FILE4, "$file1 $file2 $file3" or die "Could not print to FI
+LE4";
}
[download]

Why dont you slurp each file into any array then use a for loop to print 1 record from each file at a time

use strict;

my @file1 = ("1 G","2 F","4 H","8 T");
my @file2 = ("5 Y","6 R","7 E","8 I");
my @file3 = ("2 H","4 T","3 G","8 R");

my $largest_array = scalar @file1;
$largest_array = scalar @file2 if(scalar @file2 > $largest_array);
$largest_array = scalar @file3 if(scalar @file3 > $largest_array);

my @array =(\@file1,\@file2,\@file3);

for (my $ctr =0;$ctr <= $largest_array;$ctr++){
    print $array[0][$ctr] if($ctr <= scalar @{$array[0]});
    print $array[1][$ctr] if($ctr <= scalar @{$array[1]});
    print $array[2][$ctr] if($ctr <= scalar @{$array[2]});
    print "\n";
}

print "\n\nComplete";
[download]

A somewhat generalized solution to the problem allows a arbitrary number of files to be handled:

use strict;
use warnings;

my $file1 = <<'END_FILE';
1 G
2 F
4 H
8 T
END_FILE
my $file2 = <<'END_FILE';
5 Y
6 R
7 E
8 I
END_FILE
my $file3 = <<'END_FILE';
2 H
4 T
3 G
8 R
END_FILE

my @fileHandles;

open $fileHandles[@fileHandles], '<', $_ for \$file1, \$file2, \$file3
+;
printLines (@fileHandles);
close $_ for @fileHandles;


sub printLines {
    my @fileHandles = @_;
    my $moreLines = 1;

    while ($moreLines) {
        my $line = '';

        for my $fh (@fileHandles) {
            $line .= '  ' if length $line;
            $line .= <$fh> or return;
            chomp $line;
        }

        print "$line\n";
        $line = '';
    }
}
[download]

Prints:

1 G  5 Y  2 H
2 F  6 R  4 T
4 H  7 E  3 G
8 T  8 I  8 R
[download]

opendir(DIR,'.') or die $!;
@read=readdir(DIR);
close(DIR);
foreach(@read){
if($_ =~/^f\d.txt$/){
push(@read1,$_);
}
}
@read2=sort(@read1);
foreach (@read2){
open(FILE,$_) or die $!;
push(@file,<FILE>);
close(FILE);
push(@file,"LINE\n");
}
$string=join('',@file);
$string=~s/\n/#/g;
($val1,$val2,$val3)=split('LINE#',$string);
@val1=split('#',$val1);
@val2=split('#',$val2);
@val3=split('#',$val3);
foreach $i(0 .. scalar @val1){
print "$val1[$i]\t$val2[$i]\t$val3[$i]\n";
}
[download]