use strict;
use warnings;

my @config = qw|this oldtext needs replacement but not newtext Just oldtext|;

for (@config) {
   s/oldtext/newtext/
}

print qq|$_;\n| for @config; # "Perl" style print

for my $t (0 .. $#config){  # Your style (c-style for loop)
  print "$t:$config[$t];\n";
}

##</code><code>##

@config = map {s/oldtext/newtext/g; $_; } @config;

##</code><code>##

  map {s/oldtext/newtext/g; } @config;

##</code><code>##

 s/oldtext/newtext/ for @config;