Filenames for gnuplot via env-vars

To not have hardcoded filenames in gnuplot script

https://wiki.ubuntuusers.de/Gnuplot/#Stapelverarbeitung-Zugriff-auf-Umgebungsvariablen

euroexange/euroexange.py

@@ -213,7 +213,11 @@ class EuroExangeBot( pywikibot.bot.BaseBot ):
             os.path.join( type(self).gnuplot_script_dir,
                           job.script + ".plt" ) ) )
 
-        subprocess.call( cmd, cwd=self.wdir )
+        plt_env = os.environ.copy()
+        plt_env["INFILE"] = type(self).csv_file
+        plt_env["OUTFILE"] = job.image
+
+        subprocess.call( cmd, cwd=self.wdir, env=plt_env )
 
 
 def main(*args):

gnuplot_scripts/Euro_exchange_rate_to_TRY_-_Turkish_Currency_and_Debt_Crisis_2018.plt

@@ -3,9 +3,11 @@
 # gnuplot script for plotting eurofxref-hist.csv as obtained from
 # http://www.ecb.int/stats/exchange/eurofxref/html/index.en.html
 
+infile=system("echo $INFILE")
+outfile=system("echo $OUTFILE")
 
 # Start und Ende ermitteln (z.Zt. nur für Consolenausagabe)
-  stats 'eurofxref-hist.csv' every ::1   u (strptime("%Y-%m-%d",strcol(1))) nooutput
+  stats infile every ::1   u (strptime("%Y-%m-%d",strcol(1))) nooutput
   print '     -----Stats-(Timestamp)----'
   print '     Start:          ', strftime("%d. %B %Y",STATS_min)
   print '     Ende:           ', strftime("%d. %B %Y",STATS_max)
@@ -68,7 +70,7 @@ do for [i=1:12:2] {
 ## gnuplot for SVG - gnuplot 4.2 / Ubuntu 8.10 
 set term svg size 800,400 font "Arial,16"
 
-set outp 'Euro exchange rate to TRY - Turkish Currency and Debt Crisis 2018.svg'
+set outp outfile
 set style line 1 lt rgb 'blue' lw 1
 
 #available currencies:
@@ -76,7 +78,7 @@ set style line 1 lt rgb 'blue' lw 1
 #USD,JPY,BGN,CYP,CZK,DKK,EEK,GBP,HUF,LTL,LVL,MTL,PLN,ROL,RON,SEK,SIT,SKK,CHF,ISK,NOK,HRK,RUB,TRL,TRY,AUD,BRL,CAD,CNY,HKD,IDR,ILS,INR,KRW,MXN,MYR,NZD,PHP,SGD,THB,ZAR
 
 plot \
-  'eurofxref-hist.csv' \
+  infile \
     usi 1:($26) axis x1y1 tit '1 EUR in TRY' lt rgb 'blue' lw 1,\
-  'eurofxref-hist.csv' \
+  infile \
     usi 1:($26) axis x1y1 notit w  p lc rgb 'black' lt 1 lw 1.5 pt 7 ps 0.1 \