use diagnostics

Global symbol "$files" requires explicit package name at 1.pl line 19.
Execution of 1.pl aborted due to compilation errors (#1)
    (F) You've said "use strict" or "use strict vars", which indicates
+ 
    that all variables must either be lexically scoped (using "my" or 
+"state"), 
    declared beforehand using "our", or explicitly qualified to say 
    which package the global variable is in (using "::").
[download]

The variable $files isn't lexical. foreach (and for) uses $_ by default, but if you specify a variable name before the list, it's roughly equivalent to

foreach (@files)
{
  $files = $_;
  #etc...
[download]

So to be properly strict, you need to use my. Here are some examples of odd places where you would have to use my:

for my $i ( 0 .. 10 ) { print "$i\n" }
open my $fh, '<', "/etc/passwd";
while (my $line = <>) { next if /^\s*#/ }
[download]

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