Re: specify a multiple of m arguments in xargs

[Peng Yu]

No. I have a program that expects m*n arguments instead of just m (n
is an interger). Using `xargs -n m` would make calling the program too
many times.

On 2/21/20, Bernhard Voelker <address@hidden> wrote:
> On 2020-02-20 20:46, Peng Yu wrote:
>> Hi,
>>
>> xargs by default does not put a multiple of m arguments (m is an
>> integer greater than 1) to the command line. But is there a way that I
>> can make sure only a multiple of m arguments are put the command line.
>
> For my understanding: you have a program which would expect always
> 5 arguments from the initial input, right?
>
> For this, the input has to be structured so that it is really a multiple
> of M; otherwise, at least the last set of arguments is smaller than M.
>
>> For example, for something like the following command, I'd like to
>> make sure everytime there are 5 m arguments given to printf. But I
>> don't think xargs can guarantee so by default in the output of the
>> example.
>>
>> $ seq 1000000 | xargs printf '%s\t%s\t%s\t%s\t%s\n' > /tmp/1.txt
>> $ < /tmp/1.txt awk -v FS='\t' -e '!($1 && $2 && $3 && $4 && $5)'  | wc -l
>> 105
>
> In the above, xargs fills the command line for printf until the maximum
> command line length limit for each printf invocation.  As it doesn't
> know about the "multiple-to-M" rule, some of the lines in /tmp/1.txt
> will just contain less than M elements.
>
> What about using "xargs -n 5 ..."?
>
>   $ seq 1000000 | xargs -n 5 > /tmp/1.txt
>   $ < /tmp/1.txt awk -e '!($1 && $2 && $3 && $4 && $5)'  | wc -l
>   0
>
> Well, obviously, this will execute 'echo' many times, and therefore is
> quite slow.  Therefore, as you know the input, you can make an assumption
> of how many sets of M can be put into one command line.
>
> With the example from 'seq', it seems to be safe to put 2000 sets of M=5
> into one command line:
>
>   $ seq 1000000 | xargs -n $(( 5 * 2000 )) printf '%s\t%s\t%s\t%s\t%s\n' >
> /tmp/1.txt
>   $ < /tmp/1.txt awk -e '!($1 && $2 && $3 && $4 && $5)'  | wc -l
>   0
>
> Have a nice day,
> Berny
>


-- 
Regards,
Peng