Re: [Gnuplot-info] how to send a customized string to linux command in gnuplot

[Jon <dev...@gm...>]

Ethan,

I am curious how you quickly found out the two relevant references
towards my question given such a big volume of archived Q&E? The way
you think might help me to find out what I need in the future.

Thanks,

Sincerely,
John

On 2/11/19, Ethan A Merritt <eam...@gm...> wrote:
> On Monday, 11 February 2019 11:50:12 Jon wrote:
>> Hi,
>>
>> I need to extract a value from each file and combine a column in that
>> file and then plot. The gnuplot script looks something like
>>
>> reset; set macro
>> list="2.35 2.4 2.5 2.6 2.7 "
>> do for [i in list]{
>>   file="/dir/to/".i."/target/file"
>>   cmd="head -n 6 ".@file."  | tail -n 1 | awk '{printf $4}'"
>>   print file
>>   print cmd
>>   ef=system(@cmd)
>>   print ef
>>   plot @file u ($1-ef):2 ev ::7::301 w l ti i
>> }
>
> I do not know the reason for that exact error message,
> but the code shown cannot work as written because it is not possible
> to set and reevaluate macros inside a loop.  See for example
>
>   https://sourceforge.net/p/gnuplot/bugs/1176/
>   https://sourceforge.net/p/gnuplot/mailman/message/32364975/
>
> Fortunately as with issue #1176 there is no need to use macros at all
> in your case. The solution may be as simple as removing all those @ signs.
> I suggest you rewrite the code without macros and report back
> if there is still an error.
>
> 	Ethan
>
>
>
>> The expected screen output is, say,
>> /dir/to/2.35/target/file
>> head -n 6 /dir/to/2.35/target/file | tail -n 1 | awk '{printf $4}'
>> 3.243  (some intended value coming out of linux command, differing at each
>> i)
>> the intended plot with x axis shifted 3.243
>>
>> The execution failed complaining  "invalid expression"
>>
>> Why is the error message? Is this possibly done with gnuplot? I am
>> using gnuplot 5.2.6 on linux mint 8.1 installed in a virtualbox hosted
>> with windows 7
>>
>> Thanks for your help!
>>
>> Sincerely,
>> John
>>
>>
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> --
> entia non sunt multiplicanda praeter necessitatem
>