Yes:

1. Always use strictures (use strict; use warnings; - see The strictures, according to Seuss).
2. Always use the three parameter version of open.
3. Use lexical file handles: open my $in, '<', ...
4. Indent controlled blocks (the body of the while loop in the sample code).
5. Printing to a file you are actively reading from without an intervening seek is a bug.

Consider:

use strict;
use warnings;

my $testFileName = 'testFile.txt';
my $tempFileName = 'delme.txt';

# Create a sample file
open my $out, '>', $testFileName or die "Failed to create $testFileNam
+e: $!";

print $out <<END_STR;
be_address = remote_be_address
be_address1 = remote_be_address
be_address2 = remote_be_address
END_STR

close $out;

# The 'meat'
open my $in, '<', $testFileName;
open $out, '>', $tempFileName or die "Failed to create $tempFileName: 
+$!";

while (<$in>) {
    s/remote_be_address/192.168.106.60/g;
    print $out $_;
}

close $in or die "Failed to close $testFileName: $!";
close $out or die "Failed to close $tempFileName: $!";

unlink $testFileName;
rename $tempFileName, $testFileName;

# Show the result
open $in, '<', $testFileName;
print <$in>;
close $in or die "Failed to close $testFileName: $!";
[download]

Prints:

be_address = 192.168.106.60
be_address1 = 192.168.106.60
be_address2 = 192.168.106.60
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rename will overwrite/clobber existing filename, so you can omit unlink call

According to perlrun, -i doesn't actually edit in-place, it opens 2 filehandles and does renaming :)

That may be true, but does it matter?

--
use JAPH;
print JAPH::asString();

use strict;
use warnings;

my $infile = ...
my $outfile = ...

open IN ...
open OUT ...
while(<IN>){
...
    print OUT $_;
}
close IN;
close OUT;
rename $infile, $outfile or die "COULDN'T RENAME ($infile) to $outfile
+): $!";
[download]

why another out File handler??,
is it not possible to open the same file and replace the sting and save in to it. I need to save in the same file only ..

Please help

You might find seek helpful, and in particular this bit:

Due to the rules and rigors of ANSI C, on some systems you have to do a seek whenever you switch between reading and writing.

update: You should also think about what will happen to your file if you write directly to your original file and your modified string is shorter or longer than the original.

Because its short, its easy to understand and it works. Editing a file in-place is possible, but its nontrivial. See Re: Edit File in place for some reasons why.

It's a good idea to rename your original file to a new name, and to then write out the new version of the file to the original name. This provides an audit trail, and helps to resolve pesky questions when a change you didn't want occurrs...