comment on

I did some digging (on Windows XP, using perl 5.8.8). I didn't come up with a solution, but I thought I'd post what I found out.

I can get <$fh> to return undef by ejecting the media on which resides the file being read. close reports no error. $! is meaningless (It's "Bad file descriptor"/9 when the read is successful and when the read is not successful.)
I cannot get <$fh> (with $/ = \100) to return when the media on which resides the file being read has been ejected. It just hangs. Reinserting the media doesn't help.
I can get sysread to return undef by ejecting the media on which resides the file being read. close reports no error.
I can get read to return undef by ejecting the media on which resides the file being read. close reports "Bad file descriptor".

In all cases, I can confirm an IO error occured, since the OS pops a dialog asking to reinsert the disk once all read buffers have been emptied.

Test programs:

For <$fh>:

use strict;
use warnings;

my $file_name = 'G:\\I386\\DRIVER.CAB';  # 50MB file.

open(my $fh, '<', $file_name)
   or die("Unable to open file \"$file_name\": $!\n");

# Read 100 bytes at a time.
#binmode($fh);
#$/ = \100;

my $line;

undef $!;
$line = <$fh>;
my $ok_defined = defined($!);
my $ok_str_val = "$!";
my $ok_num_val = 0+$!;

print("Eject the media then press Enter.");
<STDIN>;

undef $!;
for (;;) {
   undef $!;
   last if not defined ($line = <$fh>);
   warn(length($line), "\n");
}
my $bad_defined = defined($!);
my $bad_str_val = "$!";
my $bad_num_val = 0+$!;

close($fh)
   or warn("Unable to read file \"$file_name\": $!\n");

print("On success, ");
if ($ok_defined) {
   print("\$! = \"$ok_str_val\"/$ok_num_val\n");
} else {
   print("\$! is not defined\n");
}

print("On failure, ");
if ($bad_defined) {
   print("\$! = \"$bad_str_val\"/$bad_num_val\n");
} else {
   print("\$! is not defined\n");
}
[download]

For sysread and read:

use strict;
use warnings;

my $file_name = 'G:\\I386\\DRIVER.CAB';  # 50MB file.

open(my $fh, '<', $file_name)
   or die("Unable to open file \"$file_name\": $!\n");

my $buf;
my $rv;

$rv = sysread($fh, $buf='', 1);
print("On success, ");
if (defined($rv)) {
   print("\$rv = $rv\n");
} else {
   print("\$rv is not defined\n");
}

print("Eject the media then press Enter.");
<STDIN>;

1 while $rv = sysread($fh, $buf='', 1);
print("On failure, ");
if (defined($rv)) {
   print("\$rv = $rv\n");
} else {
   print("\$rv is not defined\n");
}

close($fh)
   or warn("Unable to read file \"$file_name\": $!\n");
[download]

In reply to Re: Best way to handle readline errors? by ikegami
in thread Best way to handle readline errors? by jrw

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