Re: [Gnuplot-info] set xrange from variable

[Thomas S. <t.s...@fz...>]

FlavioB wrote:
> 
> ...
> Can you correct me if I'm wrong? It give 2009-11-01 because it evaluates
> the first piece of code up to "%Y"? And then it takes "-%m" and "-%d" as
> single numerical values?
> 

yes, and takes 2009-11-01 as a request to calculate the result.
and it will give an error message when %d is 07, 08, or 09
(because 0x is interpreted as an octal number).


FlavioB wrote:
> 
>> you need to make clear that you expect a string:
>> FIRST_DAY=system('date -d "-$(($(date +%d)-1)) days" 
>> +%Y-%m-%d')
>> FIRST_DAY="`date -d "-$(($(date +%d)-1)) days" +%Y-%m-%d`"
> 
> Many many thanks, but as I'm curious and willing to learn some more:
> what's the "system" word standing for?
> 

http://www.gnuplot.info/docs/node336.html
http://www.gnuplot.info/docs/node327.html


FlavioB wrote:
> 
> And how do I use double-quotes and/or single-quotes
> (like in your second example)?
> 

that's not so easy...
the outer double quotes are needed to make clear that the
result of the 'date' command is a string:

print `date -d "-$(($(date +%d)-1)) days" +%Y-%m-%d`
1997
print "`date -d "-$(($(date +%d)-1)) days" +%Y-%m-%d`"
2009-11-01

single quotes would not work here, because then the backquotes
would not be interpreted (by gnuplot):

print '`date -d "-$(($(date +%d)-1)) days" +%Y-%m-%d`'
`date -d "-$(($(date +%d)-1)) days" +%Y-%m-%d`

the double quotes inside the backquotes are essential, single
quotes would work here (due to the expansions the shell
does):

print "`date -d '-$(($(date +%d)-1)) days' +%Y-%m-%d`"
date: invalid date `-$(($(date +%d)-1)) days'

obviously, the double quotes inside the backquotes are not
interpreted as string delimiters by gnuplot, otherwise the
string would end in between.


FlavioB wrote:
> 
> Thanks again and kind regards,
> Flavio Boniforti
> 
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