this
    is just
    an example.

<Hi >
    <this>
    <is just>
    <an example.>

Hi
this
is just
an example.
<Hi >
<this>
<is just>
<an example.>
 **out.txt**

open(my $fh, "+<", "out.txt");# or die "cannot open < C:UsersdaanishsworkspaceCCoverageout.txt: $!";
     while(<$fh>)
     {
        $s1 = "<";
        $s2 = $_;
        $s3 = ">";
        $str = $s1 . $s2 . $s3;
        print $fh "$str";
     }

use Tie::File;
use strict;
use warnings;

my $filename = "out.txt";
my @array;
tie @array, 'Tie::File', $filename or die "can't tie file "$filename": $!";

for my $line (@array) {
  $line = "<$line>";
  # or $line =~ s/^(.*)$/<$1>/g; # -- whatever modifications you need to do
}

untie @array;

H  i  /  t  h  i  s  /  ...

<  H  i  >  /  i  s  /  ...

my $file;
{ # Read the file
   open(my $fh, '<', $qfn)
      or die "Can't open "$qfn": $!n";
   local $/;
   $file = <$fh>;
}

# Change the file
$file =~ s/^(.*)n/<$1>n/mg;

{ # Save the changes
   open(my $fh, '>', $qfn)
      or die "Can't create "$qfn": $!n";
   print($fh $file);
}

rename($qfn, "$qfn.old")
   or die "Can't rename "$qfn": $!n";

open(my $fh_in, '<', "$qfn.old")
      or die "Can't open "$qfn": $!n";
open(my $fh_out, '>', $qfn)
      or die "Can't create "$qfn": $!n";

while (<$fh_in>) {
   chomp;
   $_ = "<$_>";
   print($fh_out "$_n");
}

unlink("$qfn.old");

local @ARGV = $qfn;
local $^I = '';
while (<>) {
   chomp;
   $_ = "<$_>";
   print(ARGV "$_n");
}

perl -i -pe'$_ = "<$_>"' file

#!/usr/bin/perl

open(INFILE, "+<in.txt");
@a=<INFILE>;
seek INFILE, 0, SEEK_SET ;
foreach $i(@a)
{
    chomp $i;
    print INFILE "<".$i.">"."n";
}