I have multiple files in which I want to insert newline after every four lines. I know I can do it with sed but I want to do the same in perl. I have tried the following code: 
use strict;
    use warnings;
my @files= @ARGV;
   for my $input_file (@files) {

   system "sed -i '0~4 s/\$/\n/g' $input_file";
    
}

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when I substitute it with any string it is done but when I am inserting newline as in above code it is giving error. I don't want to do it with sed as I know sed works only in linux. If someone can help me to insert a newline after every four lines using perl and not sed.

In reply to put a newline character after every four lines in a file by Anonymous Monk

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