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

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

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

 s/oldtext/newtext/ for @config;