Re: How to get the default value of --max-args?

[Peng Yu]

On Thu, Nov 8, 2018 at 4:50 AM Bernhard Voelker
<address@hidden> wrote:
>
> On 11/8/18 6:50 AM, Peng Yu wrote:
> > Hi,
> >
> > It seems that the default value for --max-args is system dependent. Is
> > there a way to find out its default value? Thanks.
>
> Actually the limit is not a matter of the number of arguments but that
> of the resulting total command line length.
>
> From 'man xargs':
>
>   --show-limits
>        Display the limits on the command-line length which are imposed by the
>        operating system, xargs' choice of buffer size and the -s option.
>        Pipe the input from /dev/null (and perhaps specify --no-run-if-empty)
>        if you don't want xargs to do anything.
>
> So here it is:
>
>   $ xargs --show-limits </dev/null
>   Your environment variables take up 3163 bytes
>   POSIX upper limit on argument length (this system): 2091941
>   POSIX smallest allowable upper limit on argument length (all systems): 4096
>   Maximum length of command we could actually use: 2088778
>   Size of command buffer we are actually using: 131072
>   Maximum parallelism (--max-procs must be no greater): 2147483647
>
> It's "actually using: 131072".
>
> So even if you specify a higher number like 'xargs -n 200000', and all the
> arguments only have 1 character, then still the number of actual arguments
> for each program execution cannot be larger than about 131072/2 minus a few
> bytes:
>
> echo called only once:
>
>   $ yes . | head -n $(bc <<<'131072 /2 - 3') | xargs -tn 200000 2>&1 | tr -d 
> '[. ]'
>   echo
>
> echo called twice:
>
>   $ yes . | head -n $(bc <<<'131072 /2 - 2') | xargs -tn 200000 2>&1 | tr -d 
> '[. ]'
>   echo
>   echo

Thanks. But I am not getting the same results (not the same number of
echo's) as yours. I am using Mac OS X. Do you know why it is
different?

$ xargs --show-limits < /dev/null
Your environment variables take up 7701 bytes
POSIX upper limit on argument length (this system): 252395
POSIX smallest allowable upper limit on argument length (all systems): 4096
Maximum length of command we could actually use: 244694
Size of command buffer we are actually using: 131072
Maximum parallelism (--max-procs must be no greater): 2147483647

$ yes . | head -n $(bc <<< '131072/2 - 3') | xargs -tn 200000 2>&1 |
tr -d '[. ]'
echo
echo

echo

echo
echo
echo
echo

echo

echo

$ yes . | head -n $(bc <<< '131072/2 - 2') | xargs -tn 200000 2>&1 |
tr -d '[. ]'
echo
echo

echo

echo
echo
echo
echo

echo

echo

-- 
Regards,
Peng