Hi,
Try with the following.

use Tie::File;
use Fcntl 'O_RDONLY','O_RDWR';
my @file1;
my @file2;
my $file1;
tie @file1, 'Tie::File', "fileA",mode => O_RDONLY;
tie @file2, 'Tie::File', "fileB",mode => O_RDWR;
$file1=join("\n",@file1);

for($i=0;$i<=$#file2;$i++)
{

   next unless($file2[$i]=~s/(SEARCHPATTERN)/$1\n$file1/)

}
[download]

fileA<br>
1
2
3
4
5

fileB
a
b
c
d
SEARCHPATTERN
e
f
g
h
i

Ouput(fileB)
a
b
c
d
SEARCHPATTERN
1
2
3
4
5
e
f
g
h
i
[download]