I have one more query on this.

In following Environment File I am giving only values of parameters which would be replaced in properties file

DOMAIN=<value>
DOMAIN_TEST_DB_CONN_STR=<value>
DOMAIN_TEST_DB_USER=<value>
DOMAIN_TEST_DB_PSWD=<value>
[download]
[download]

Followin Properties File have other lines too which do not match those from environment files above.

#These are the properties for engineering
#We expect you to change them for your environment
#
#CustomerDatabase info
DOMAIN=<value>
DOMAIN_TEST_DB_CONN_STR=<value>
DOMAIN_TEST_DB_USER=<value>
DOMAIN_TEST_DB_PSWD=<value>
[download]

My objective is to replace values of properties file based on environment file at same time keeping non matching lines as it is. If I use the following code, duplicate lines will be printed for every line from environment file.

use strict;
use warnings;

my $envfile = "/root/env.properties"; 
my $file = 'input.txt'; # Or whatever

open my $env,  '<',  $envfile      or die "Can't read old file: $!";
open my $in,  '<',  $file      or die "Can't read old file: $!";
open my $out, '>', "$file.new" or die "Can't write new file: $!";

my @envFile = <$env>;
my @inFile = <$in>;

print "\nFile contents:";
print @envFile;

my $dbhost = '';
my $dbport = '';
my $dbschema = '';

foreach my $envline (@envFile){
    my $inLineCount = 0;
    foreach my $inline (@inFile){
        $inLineCount++;
        print "$inLineCount $inline";
        foreach my $DOMAIN_DB_CONN_STR ('FINANCE_DB_CONN_STR', 'MARKET
+ING_DB_CONN_STR') {
            if($envline =~/$DOMAIN_DB_CONN_STR=.*:1521:.*/ && $inline 
+=~/$DOMAIN_DB_CONN_STR=.*:1521:.*/){
                print "\nMatch";
                my $line = $inline;
                $line =~ s/$DOMAIN_DB_CONN_STR=.*:1521:.*/NUANCE_DB_CO
+NN_STR=$dbhost:$dbport:$dbschema/;
                print $out $line;
            } else {
                  print $out $line;
            }
        }
    }
}
[download]

Output would be

#These are the properties for engineering
#We expect you to change them for your environment
#
#CustomerDatabase info
DOMAIN=<value>
DOMAIN_TEST_DB_CONN_STR=<value>
DOMAIN_TEST_DB_USER=<value>
DOMAIN_TEST_DB_PSWD=<value>


#These are the properties for engineering
#We expect you to change them for your environment
#
#CustomerDatabase info
DOMAIN=<value>
DOMAIN_TEST_DB_CONN_STR=<value>
DOMAIN_TEST_DB_USER=<value>
DOMAIN_TEST_DB_PSWD=<value>


#These are the properties for engineering
#We expect you to change them for your environment
#
#CustomerDatabase info
DOMAIN=<value>
DOMAIN_TEST_DB_CONN_STR=<value>
DOMAIN_TEST_DB_USER=<value>
DOMAIN_TEST_DB_PSWD=<value>

#These are the properties for engineering
#We expect you to change them for your environment
#
#CustomerDatabase info
DOMAIN=<value>
DOMAIN_TEST_DB_CONN_STR=<value>
DOMAIN_TEST_DB_USER=<value>
DOMAIN_TEST_DB_PSWD=<value>
[download]

Could you please let me know how to handle this?

Thanks in advance!!