You already are on the right path ( strict and warnigns are there ) but maybe you need to use some idioms more: firstly the use of the better form to open a file: lexical filehandle, checking if all was good: open my $h, '<', $file or die "cannot read from $file!"

Another common way, idiomatic way of Perl thinking is: uniqueness, quantity or existence of something lead immediately to use an hash. You read a list populating the hash with each item and later on you'll be able to check against this list as simply as:  .. if exists $files{$current_element}

But given your numbers (300 files is not a big deal nowadays..) you can also do all the work directly while reading the list file:

..
my $list_file = '/path/to/list.txt';

open my $read, '<', $list_file or die "cannot read from'$list_file'!";

while (<$read>){  # it populates $_ is the same of: defined $_ = <$rea
+d>
  chomp;
  my $ret = process ($_) if -e "./$_";
  if ($ret){print "$_ succesfully processed\n"}
  else{print "Warning: '$_' was not processed!\n"}
}

sub process{
 my $file = shift;
 open ... or return 0
 # read and do something
 close ..
 # implicitly return the last thing: if close succeded is 1 
}
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