an alternative also is, if you prefer to use as much as less modules possible:

#!/usr/bin/perl

use strict;
no warnings;

foreach my $in (@ARGV){
  my($copy) = "$in.bak";
  copy($in, $copy) or die "File cannot be copied. \n";

  open(INPUT,"$copy") or die 'Cannot open file: $!\n';
  open(OUTPUT,">$in");

  my($replacePattern1) = "foo1";
  ...
  
  
}
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or if the files are in a dir then use the readdir function, collect all the files from the dir and loop over them like in the example before

opendir(DIR, $ARGV[0]) || die "i died for no reason ;)\n";
 
foreach (readdir DIR){
  #repeat like above
  #watch out for defining the right path to dir and when looping re-ty
+pe the fool path to your dir, like:
  # open (FILE, ">", "$ARGV[0]/$_") || die "i died for no reason ;)\n"
}
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