$a = "dflsdgjsdg
dsfsd
gf
sgd
g
sdg
sdf
gsd";

$a = "dflsdgjsdg dsfsd gf sgd g sdg sdf gsd"

#!/usr/bin/perl

use strict;
use warnings;

my $x = q{dflsdgjsdg
dsfsd
gf
sgd
g
sdg
sdf
gsd};

$x =~ tr{n}{ };

print $x, "n";
__END__

C:Temp> ttt
dflsdgjsdg dsfsd gf sgd g sdg sdf gsd

#!/usr/bin/perl

use strict;
use warnings;

use Benchmark qw( cmpthese );

use constant LONG_STRING => "n" x 1_000_000;

cmpthese -10, {
    subst => sub {
        my $x = LONG_STRING;
        $x =~ s{n}{ }g;
        return;
    },
    split_join => sub {
        my $x = LONG_STRING;
        $x = join ' ', split /n/, $x;
        return;
    },
    tr => sub {
        my $x = LONG_STRING;
        $x =~ tr{n}{ };
        return;
    },
    nop => sub {
        my $x = LONG_STRING;
        return;
    }
};
__END__

Rate split_join      subst         tr        nop
split_join 0.354/s         --       -85%      -100%      -100%
subst       2.40/s       578%         --       -99%      -100%
tr           250/s     70514%     10320%         --       -92%
nop         3025/s    854076%    125942%      1110%         --

#!/usr/bin/perl

use strict;
use warnings;

my $a = 'dflsdgjsdg
dsfsd
gf
sgd
g
sdg
sdf
gsd';
$a =~ s{n}{ }g;

print $a;

$a = "dflsdgjsdg
dsfsd
gf
sgd
g
sdg
sdf
gsd";

$a =~ s/n/ /g;
print $a;

@s =split /n/,$a;
print join(" ",@s);

$a = "dflsdgjsdg
dsfsd
gf
sgd
g
sdg
sdf
gsd";

$a =~ s/n/ /g;

$a =~ tr/n/ /;

$a = join " ", split "n", $a;