Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!etnibsd!vsh
From: vsh@etnibsd.UUCP (Steve Harris)
Newsgroups: comp.lang.perl
Subject: perl will not open block-special files
Message-ID: <1108@etnibsd.UUCP>
Date: 8 Feb 90 19:35:57 GMT
Organization: Eaton Corp, Semiconductor Equipment Div., Beverly, MA
Lines: 53


I wrote a little script to read disk blocks.  It starts with
the following two lines:

	$DEV = "<" . $ARGV[0];		# make sure DEV is opened for reading
	open DEV || die "cannot open $DEV";

The open works fine when I open a character device, but fails when I
try to open a block device:

	perl test.pl /dev/xy0c		# fails; xy0c is block-special
	perl test.pl /dev/rxy0c		# okay; rxy0c is character-special

If I open stdin and use shell redirection to associate stdin with the
file, the open succeeds:

	perl test.pl - < /dev/rxy0c	# okay; open stdin

So I dug into the source, and found, in "doio.c", the following code:

/**********************************************************/
    if (stio->type &&
      stio->type != '|' && stio->type != '-') {
	if (fstat(fileno(fp),&statbuf) < 0) {
	    (void)fclose(fp);
	    return FALSE;
	}
	if ((statbuf.st_mode & S_IFMT) != S_IFREG &&
#ifdef S_IFSOCK
	    (statbuf.st_mode & S_IFMT) != S_IFSOCK &&
#endif
#ifdef S_IFFIFO
	    (statbuf.st_mode & S_IFMT) != S_IFFIFO &&
#endif
	    (statbuf.st_mode & S_IFMT) != S_IFCHR) {
	    (void)fclose(fp);
	    return FALSE;
	}
    }
/**********************************************************/

I'm not sure what's going on here, but it sure looks like perl wants
the device to be either regular, character-special, socket, or fifo.

Why is this?  Is it necessary?  Is this "fixed" with a patch I haven't
had time to obtain and install?  (I'm running 3.0, patch level 1; I
know I should get up to date but it works well enough that I have not
done so, yet.)

Also, in the scripts in the perl library, every comment line begins
with ";#", not just "#".  Why is this?  (Inquiring minds, etc.)
-- 
Steve Harris - Eaton Corp. - Beverly, MA - uunet!etnibsd!vsh