As described in $! and Error Indicators in perlvar, "A successful system or library call does not set the variable [$!] to zero." This means you cannot test $! and expect to get a meaningful result. Note that despite your reported error, your code executes the script with no problem. Consider: 

#!/usr/bin/perl
use strict; use warnings;
my $do_me="do_me.pl";
print "(1)Can not read $do_me: $!\n" if $!;
foreach my $ending ("\n", '') {
  print "Create file with",($ending?'':'out')," newline\n";
  open(OUT,'>',$do_me) or die "$!";
  print "(2)Can not read $do_me: $!\n" if $!;
  print OUT "q(string)$ending";
  close OUT;
  my $result=do $do_me;
  print "(3)Can not read $do_me: $!\n" if $!;
  print "Can not evaluate $do_me: $@\n" if $@;
  print("$result\n") if defined $result;
}
print "(4)Can not read $do_me: $!\n" if $!;

[download]

outputs: 

(1)Can not read do_me.pl: Bad file descriptor
Create file with newline
(2)Can not read do_me.pl: Bad file descriptor
string
Create file without newline
(3)Can not read do_me.pl: Bad file descriptor
string
(4)Can not read do_me.pl: Bad file descriptor

[download]

As to why you get that pattern, my guess is internal try-catch structures within the open and do blocks.

In reply to Re: Why do we need a \n with do FILENAME? by kennethk
in thread Why do we need a \n with do FILENAME? by rovf

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