lp (-h) hostname option has to come before destination (-d)

[debiantriage]

Debian user Paul Hutschemaekers has reported

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1008210

lp -d DESTINATION -h HOSTNAME FILENAME fails, whereas lp -h HOSTNAME -d DESTINATION FILENAME succeeds. I have reproduced this behaviour with 2.3.3op2 and 2.4.1op1 but not with 2.2.10-6.

--
Brian.

[tillkamppeter]

This is due to the fact that CUPS' command line tools do not parse the complete command line before executing the command, but instead, parse each argument, one by one, and execute it. So in the first command line of your example it parses and executes -d DESTINATION first and fails as DESTINATION is not available on the local machine but only on the remote machine HOSTNAME. The second command line parses and executes -h HOSTNAME first and switches to HOSTNAME after that it parses and executes -d DESTINATION and succeeds to find DESTINATION, then being able to send FILENAME for printing.

This is the architecture of the tools which @michaelrsweet has chosen more than 22 years ago when he started developing CUPS. I do not know whether other command line tools of that time (and also of today) also work this way. Perhaps it was common that time at least.

More intuitive for a user would be to parse the full command line at first and then execute the whole thing.

[jsmeix]

So the syntax in the lp man page is wrong (or at least misleading):
https://openprinting.github.io/cups/doc/man-lp.html

lp [ -E ] [ -U username ] [ -c ] [ -d destination[/instance] ] [ -h hostname[:port] ] ...

In general the sequence of the options is significant.
For example, the following commands are all different:

lpadmin -E -p queue,
lpadmin -p queue -E
lpadmin -E -p queue -E

but here the lpadmin man page describes it correctly.

[debiantriage]

@tillkamppeter Thanks for the explanation. But note: either command works on Debian's CUPS 2.2.10-6+deb10u4. Where does that leave us?

@jsmeix A documentation bug then? (With lpadmin I understand the double use of -E lies way back in the history of CUPS).

[michaelrsweet]

@tillkamppeter Parsing all arguments first would change behavior, not to mention making those programs significantly more complex.

@debiantriage The "-E" option to lpadmin goes back to System V's "lp" command (enable and accept jobs) while "-E" for the CUPS commands forces encryption to be used. So what happened for lpadmin was a bit of a compromise for consistency's sake...

As for "-h" working before or after, it is probably because the queue is accessible from both the default and external servers...

[debiantriage]

@michaelrsweet I'll accept the behaviour and complexity argument. Will the documentation be altered to reflect the order -h, -d?

[zdohnal]

@debiantriage I've hit the similar issue with lpstat in RHEL - user was confused by order dependency - so the idea was to create a new subsection in manpages - 'Connect options' - so users can see those have to before other options.

So the synopsis would be:

lpadmin [ connect options] -d destination
lpadmin [ connect options ] -p destination
...

WDYT?

[michaelrsweet]

@zdohnal I'd call them "connection options" or (better?) "server options". The point is that "-h" and "-E" need to come before other options.

[debiantriage]

@zdohnal A good idea. I would incline slightly towards Server options.

--
Brian.

[michaelrsweet]

[master 4d6787b] Update man pages for -h option (Issue #357)