Re: [Gnuplot-info] failure to change directory and execute linux command

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

Wow! This is likely the case. Thank you so much for your explanation.

Sincerely,
Jon

On 6/24/20, Ethan Merritt <eam...@gm...> wrote:
> On Tuesday, 23 June 2020 14:26:41 PDT Jon wrote:
>> Hi,
>>
>> I am trying to execute a script ssss.gn within gnuplot 5.2.2 in
>> linuxmint 18.2 including the following lines
>> pwdd="`pwd`"
>> do for [ dir in "4.1 4.15 4.2 4.25 4.3 "] {
>>   print dir
>>   cd dir."/right/here/waiting/"
>>   ef=`head -n 1 DOSCAR | awk '{print $5}'`
>>   print ef
>>   cd pwdd
>> }
>>
>> but it complains
>
> I do not fully understand this myself, but I do know how avoid the problem.
> There is a subtle difference between
>       foo = "`some command`"
> and
>       foo = system("some command")
>
> in that the back-quote version is evaluated during command parsing,
> while the system() command is evaluated during execution.
> I am not sure why exactly that matters in your case but apparently it does.
>
> You can fix it by replacing the back-quotes with a system command
>
> pwdd = system("pwd")
> do for [ dir in "4.1 4.15 4.2 4.25 4.3 "] {
>   print dir
>   cd dir."/right/here/waiting/"
>   ef = system("head -n 1 DOSCAR | awk '{print $5}'")
>   print ef
>   cd pwdd
> }
>
>> gnuplot> load "ssss.gn"
>> head: cannot open 'DOSCAR' for reading: No such file or directory
>> 4.1
>>          line 5: constant expression required
>>
>> but the file does exist under the directory, why would it complain
>> file not existing
>>
>> Another confusing observation is the error concerning nonexistence of
>> DOSCAR comes before the print statement in the script. Why is that?
>
> It is a symptom of the back-quote evaluation occuring during an
> earlier stage of processing than the loop execution.
>
> 	Ethan
>
>
>>
>> Thanks,
>>
>> Sincerely,
>> Jon
>
>
>
>