Without seeing your "somefile.txt" I'm not sure what you are doing to get your $word. Certainly, the second chomp is superfluous as you can't remove the line terminator twice. My code below is the equivalent of yours except that I don't do the final chop as I can't tell whether it was necessary; it's easy enough to add back in. I perform the parsing of "somefile.txt" in a BEGIN {...} block before going on to append to the lines in the "address" file.

moritz points out that it can be a bad idea to edit a file in place. Perl does, however, have a handy -i flag for in-place editing which, if given an extension, will preserve your original file with that extension, the modified file taking the original name. Given a spurious "tcp" file and an "address" file

$ cat spw638403.txt
aajkaj  XYZtcpHJHKtcpKJHKH
ashhgdasjh    JKHKJHtcpUUHtcpHDKJHtcpJHDJAHD
kjkjn  NHYtcpHHGJJH
$ cat spw638403.addr
Address1=
Address2=
Address3=
$
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running this code (note the -i.bak flag

#!/usr/bin/perl -i.bak
#
use strict;
use warnings;

my @list = ();

BEGIN
{
    my $inFile = q{spw638403.txt};
    open my $inFH, q{<}, $inFile
       or die qq{open: $inFile: $!\n};

    while ( <$inFH> )
    {
        chomp;
        push @list, ( split m{tcp}, ( split )[1] )[0];
    }

    close $inFH
       or die qq{close: $inFile: $!\n};
}

while ( <> )
{
    s{$}{$list[$. - 1]};
    print;
}
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with the address file as the argument results in the original file preserved as spw638403.addr.bak and the modified file as spw638403.addr

$ ./spw638403 spw638403.addr
$ cat spw638403.addr
Address1=XYZ
Address2=JKHKJH
Address3=NHY
$
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I hope this is of use.

Cheers,

JohnGG

Update: Clarified point that the scripts needs the name of the file to be modified as an argument.

Update 2: Corrected senior moment with flag. It is, of course, the -i flag, not -p