Your snipped might work for your PC only and you'll only see the last /dev/sr device - which might not be a CD or DVD at all. The following suggestion is only a tiny improvement: 

use strict;

# returns list of CD/DVD mountpoints or empty list
sub scan_cddvd { 
    my @drives   = ();
    my $mtabfile = "/etc/mtab";

    open my $mtfh, "<", $mtabfile or die "cannot open $mtabfile - $!";
    while( <$mtfh> ){
      my ($dev, $mountpoint, $fstype, $options) = split /\s+/;
      next unless $fstype =~ /udf|iso\d+/ && $options =~ /ro\b/; 
      #ro: the /ro/-test above should skip CDRW too
      $mountpoint =~ s/\\(0\d+)/chr(oct($1))/eg;  # resolve oct chars
      push @drives, $mountpoint;
    }
    close $mtfh;

    return @drives;
}

print "o <", join(">\no <", scan_cddvd), ">\n";

[download]
Things to note: uses strict; avoids "not found" as a special failure-indicator; returns list of mountpoints; expands all octal escapes; less HW-dependent (e.g. IDE, SCSI, SATA, ...), e.g. not restricted to /dev/sdb; tries a little harder to find a CD or DVD (iso/udf,ro), uses 3 param open and die; no globs (MYINPUTFILE); implicit use of $_; will fail for derviant mtab-formats; ...

In reply to Re^2: Detect Plugged USB Flash Drive / CD in CDROM Drive by Perlbotics
in thread Detect Plugged USB Flash Drive / CD in CDROM Drive by renegadex

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