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";
}