So this? Its a common pattern; 
while(<$in>){
   print $out $_;
   if( /word/ ){
      print $out scalar <$in>, "APPEND";
   }
}
close $in;
close $out;
rename $outfile, $infile;

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In reply to Re^3: search for string append in file by Anonymous Monk
in thread search for string append in file by Bronston

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