Re: TAB character in groff output

[Alejandro Colomar]

Hi Ingo,

On 8/2/22 15:44, Ingo Schwarze wrote:
> Hi Alejandro,
>
> Alejandro Colomar wrote on Tue, Aug 02, 2022 at 02:14:58PM +0200:
>
> > I'd like to be able to produce ASCII HT ('\t' - horizontal tab) in man
> > pages output.  I don't want to align things; I do want a tab character.
> > Rationale: examples in fstab(5).
>
> I don't understand.  On Debian, fstab(5) is part of the "mount"
> package - which seems very reasonable to me - and it says:

Ahh, I was talking a bit from memory.  It wasn't fstab(5), but spufs(7), 
which has an example of an fstab entry:

EXAMPLES
       /etc/fstab  entry
              none      /spu      spufs     gid=spu   0    0

>    Fields on each line are separated by tabs or spaces.
>
> What's wrong with using spaces?

Nothing very wrong.  I was just wondering if tabs were possible. 
fstab(5) might accept spaces (although I wouldn't use them in a real 
fstab file, actually; and I guess you can only use single spaces, or 
maybe not... never tried), but maybe some other software doesn't.

> Wanting to show literal tab characters to users in a manual page
> seems a dubious goal to me for two reasons:
>
>   * They are visually indistinguishable from spaces, so if the
>     distinction really matters, confusion is almost guaranteed to ensue.

Of course, if it matters, some description about it is needed.

>   * Some users may use pagers that convert tabs to spaces or vice
>     versa, so even if you hope for pastability, you still need
>     luck for it to work as intended.

Yeah, I wanted this.  But, less(1) doesn't seem to like tabs :(, the 
same as mandoc(1).  The first time I like more(1) better than less(1); 
of course it has at least one more feature ;)

> > Is that possible?  I didn't find anything in groff_char(7).
>
> In groff, this works for me:
>
>   $ printf "a\\\\N'9'b" | groff -T ascii | hexdump -C | head -n 1
> 00000000  61 09 62 0a 0a 0a 0a 0a  0a 0a 0a 0a 0a 0a 0a 0a  |a.b.............|
>
> Mandoc behaves differently and treats \N'9' exactly like a literal HT:
>
>   $ printf "a\\\\N'9'b" | mandoc | hexdump -C | grep 61
> 00000050  61 20 20 20 20 62 0a 0a  20 20 20 20 20 20 20 20  |a    b..        |
>
> In general, mandoc lets fewer control characters sneak through into
> output than groff because i worry that control characters in output
> might occasionally cause reliability or security issues.

I have to fix some warnings:

$ make lint-man-mandoc
LINT (mandoc)   tmp/lint/man7/spufs.7.lint-man.mandoc.touch
mandoc: man7/spufs.7:748:7: WARNING: tab in filled text
mandoc: man7/spufs.7:748:14: WARNING: tab in filled text
mandoc: man7/spufs.7:748:22: WARNING: tab in filled text
mandoc: man7/spufs.7:748:32: WARNING: tab in filled text
mandoc: man7/spufs.7:748:34: WARNING: tab in filled text
make: *** [lib/lint-man.mk:54: 
tmp/lint/man7/spufs.7.lint-man.mandoc.touch] Error 2

In the following code:

$ sed -n 745,749p <man7/spufs.7
.SH EXAMPLES
.TP
.IR /etc/fstab "  entry"
none    /spu    spufs   gid=spu         0       0
.\" .SH AUTHORS


$ sed -n 748p <man7/spufs.7
none    /spu    spufs   gid=spu         0       0


$ sed -n 748p <man7/spufs.7 | hexdump -C
00000000  6e 6f 6e 65 20 20 09 2f  73 70 75 20 20 09 73 70  |none  ./spu 
 .sp|
00000010  75 66 73 20 20 09 67 69  64 3d 73 70 75 20 20 09  |ufs 
.gid=spu  .|
00000020  30 09 30 0a                                       |0.0.|
00000024


That code is very broken: SP SP HT sequences

I think I'll fix it with tbl(1).

Cheers,

Alex


> Yours,
>    Ingo

--
Alejandro Colomar
<http://www.alejandro-colomar.es/>

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