sed is eating my null. 1

[motoslide]

I've got a script (I didn't create) that is being used as an Output filter to convert NL to CRNL. It works fine, but I don't understand it enough to fix an issue.
I have another script that will send a single-byte file to a printer just to wake it up. That single byte is a hex "00" (null).
The CRNL filter below eats up the null and creates a completely EMPTY print stream, of which the spooler refuses to act upon.

Here's the filter/script:

:
# addcr - filters to add CARRIAGE RETURN to LINEFEED in text
#
#       addcr adds CR to each LF
#
CR=`echo | tr '\012' '\015'`
sed "s/$/$CR/" $*

When i pipe my nullfile to the script, the output is completely empty (as verified using "hd").

Is there a way I can either allow the null to pass unaffected, or set a conditional so this script is only invoked if the data in the pipe is > 2 bytes long?

"Proof that there is intelligent life in Oregon. Well, Life anyway.

 

[feherke]

Hi

I think you will have to give us more details about the circumstances, because that code works for me. Or am I misunderstanding something ?

[blue]master[/blue] CR=`echo | tr '\012' '\015'`

[blue]master[/blue] perl -e 'print chr 0' | sed "s/$/$CR/" | od -a
0000000 nul  cr
0000002

[blue]master[/blue] perl -e 'print chr 0,"\n"' | sed "s/$/$CR/" | od -a
0000000 nul  cr  nl
0000003

Feherke.

http://rootshell.be/~feherke/

 

[motoslide]

Thanks, Feherke.
What is actually happening, is that I have this specified in my /etc/printcap file:

p4tst:\
:lp=:rm=p4a:rp=raw1:sd=/usr/spool/lpd/p4tst:mx#0f=/usr/local/bin/lp_addcr

This is "lp_addcr":
#!/bin/sh
exec /usr/local/bin/addcr_lpd

The script in my original post is the contents of "addcr_lpd".

This is my experiment:

$ hd nullfile
0000    00                                                 .
0001
$ cat nullfile |addcr_lpd|hd
0000
$ cat nullfile|hd
0000    00                                                 .
0001

I'm aware of the UUOC infraction(s). It's Friday, I'm feeling exempt.


"Proof that there is intelligent life in Oregon. Well, Life anyway.

 

[Annihilannic]

What OS, moto? Is unix2dos not available?

Annihilannic.

 

[motoslide]

I'm running SCO (mostly) and little Linux. Are you saying I could incorporate "xtod" (SCO's version of unix2dos) as an output script?
I'll have to give that a try tomorrow.

The script I listed in my first post came from SCO's knowledge-base, so I just figured xtod wouldn't fly for some reason.



"Proof that there is intelligent life in Oregon. Well, Life anyway.

 

[PHV]

AFAIK, xtod adds a Ctrl-Z at the end of the converted file...

 

[motoslide]

I end up with the same issue (as PHV expected). When I run the job through xtod, it adds a trailing Ctrl-Z, which I can chop off using sed, but, again, sed eats my null.

I tried piping the output to awk using "^Z" as the field seperator. The result is a loss of the null character, plus the addition of an unwanted LF.

cat nullfile|xtod|awk -F "^Z" '{ print $1 '}|hd
0000     0a

I came up with a way to accomplish my needs, but it's pretty clunky. I've replace the original "addcr_lpd" with this:

xtod > /usr/tmp/testfile.$$
SIZE=`wc -m /usr/tmp/testfile.$$|awk '{ print $1 '}`
SIZE=`expr $SIZE - 1`
dd if=/usr/tmp/testfile.$$ bs=1 count=$SIZE 2>/dev/null
rm /usr/tmp/testfile.$$

This adds the "CR" to text files (which I need) and it also allows my 1-byte NULL file to pass through, which is used to restart a hung lpd printer.

I hate the idea of creating an interrim file just to chop off the last byte. Any other ideas?



"Proof that there is intelligent life in Oregon. Well, Life anyway.

 

[Annihilannic]

If perl is available on those systems, why not just use that to do the sediting, since it seems to honour the nulls it is given?

$ perl -e 'print "hello\nw " . chr(0) . "rld\n";' | perl -pe 's/\n/\r\n/'| od -c
0000000    h   e   l   l   o  \r  \n   w      \0   r   l   d  \r  \n
0000017

Annihilannic.

 

[motoslide]

The perl option works perfectly.
Thanks!



"Proof that there is intelligent life in Oregon. Well, Life anyway.