1) perl -nle '$result .= " $_"; END{print $result}' data.txt

2) perl -e "chomp(@lines=<>); print join ' ', @lines" data.txt


##</code><code>##

perl -e 'undef $/;  $text=<>; $text =~ tr/\n//; 1 while $text =~ s/\b(
+\w+\d+\s*\d+\.\d+\.\d+\.\d+)\s*\1\b/$1/ig; print $text; $/="\n"; list


##</code><code>##

use strict;
use warnings;
use 5.010;

my $text = 'S55 1.1.1.1 S66 2.2.2.2 S55 1.1.1.1';
$text =~ s/\b(\w+\d+\s*\d+\.\d+\.\d+\.\d+)\s*\1\b/$1/ig;

say $text;

--output:--
S55 1.1.1.1 S66 2.2.2.2 S55 1.1.1.1



##</code><code>##

perl -nle '$results{$_}=undef; END{print join " ", keys %results}' data.txt