[9fans] -- in rsc's g script

[9fans] -- in rsc's g script

[Rudolf Sykora]

Hello,

could anybody tell me what's the meaning of '--' in

grep -n $flags -- $1 *.[Cbchm] /dev/null

?
This I found in Russ Cox's g script.

Thanks
Ruda

Re: [9fans] -- in rsc's g script

[Steve Simon]

see arg(2) for all the details.

-- indicates the end of any options, it ensures that any following
arguments which happen to begin with a minus are not interpreted
as options.

consider the classic question: "how do I remove a file called -z"

-Steve

Re: [9fans] -- in rsc's g script

[Richard Miller]

> consider the classic question: "how do I remove a file called -z"

rm ./-z

Re: [9fans] -- in rsc's g script

[Robert Ransom]

On Sat, 15 May 2010 15:16:35 +0200
Rudolf Sykora <rudolf.sykora@gmail.com> wrote:

> could anybody tell me what's the meaning of '--' in
>
> grep -n $flags -- $1 *.[Cbchm] /dev/null

'--' tells the Plan 9 program argument parser to stop looking for
options.  See arg(2).

GNU getopt has the same feature.

Robert Ransom

Re: [9fans] -- in rsc's g script

[Rudolf Sykora]

> '--' tells the Plan 9 program argument parser to stop looking for
> options.  See arg(2).

so is it a program dependent feature in the sence that I must know
which program uses arg(2) and which does not?
(E.g that grep uses it but some other command (is there any?) does not?)
Must I read the program's source or should it be documented in man
pages? -- there is nothing about this in the man page of grep...

Thanks
Ruda

Re: [9fans] -- in rsc's g script

[Steve Simon]

I don't beleive greps manual page says it writes its output to file descriptor 1
and reaqds from file descriptor zero but it does, as do all conventional (sic)
plan9 programs. Similarly they all use arg(2) to parse their args so they will
all support --; however if you are unsure you could look at the source, yes.

-Steve

Re: [9fans] -- in rsc's g script

[erik quanstrom]

On Sat May 15 09:54:25 EDT 2010, rudolf.sykora@gmail.com wrote:
> > '--' tells the Plan 9 program argument parser to stop looking for
> > options.  See arg(2).
>
> so is it a program dependent feature in the sence that I must know
> which program uses arg(2) and which does not?
> (E.g that grep uses it but some other command (is there any?) does not?)
> Must I read the program's source or should it be documented in man
> pages? -- there is nothing about this in the man page of grep...

for the record, grep also accepts -e which escapes the next option.

here's a list of all the single-file commands in /sys/src that don't
use ARGBEGIN/ARGEND.  compiling a comprehensive list is
an exercize left to the reader.  of course, only a hand full of
shell scripts use getflags and conform to the general convention.

- erik

---

 ; x=`{grep -l ARGBEGIN *.c}
; for(i in *.c) if (! ~ $i $x) echo $i
ar.c
awd.c
basename.c
cal.c
cat.c
chmod.c
clock.c
dd.c
echo.c
factor.c
fortune.c
getmap.c
html2ms.c
join.c
kbmap.c
kprof.c
lens.c
mc.c
msleep.c
mv.c
p.c
pbd.c
pr.c
pwd.c
sleep.c
sort.c
swap.c
tail.c
test.c
time.c
tprof.c
uniq.c
unlnfs.c
unmount.c
xd.c