Why my commands do not work for gnuplot?

Question

I have input file test.dat that contains

I wrote the script for gnuplot:

gnuplot <<EOF
set term png size 1000,1000;
set output "out.png";
set arrow from graph 0,1 to graph 0,1.1 filled
set arrow from graph 1,0 to graph 1.1,0 filled
set tmargin 5
set rmargin 20
set border 3
set tics nomirror
set grid
set xtics font "Verdana,14"
set ytics font "Verdana,14"  
set nokey
set style line 1 lt 1 lw 3 pt 3 linecolor rgb "black"
set ylabel "Efficiency, %" offset 2,0,0 font "Verdana,14"
set xlabel "Cores, N" offset 0,0,0 font "Verdana,14"
func1(x) = x / 2
func2(x) = x * 2
plot "test.dat" u (func1($1)):(func2($2)) ls 1 smooth csplines;
EOF

But the error occurs when you try to start it:

gnuplot> plot "test.dat" u (func1()):(func2()) ls 1 smooth csplines;
         line 0: invalid expression

Christoph · Accepted Answer · 2016-07-13 05:08:51Z

3

The dollar signs are interpreted as starting a shell variable. Use column instead:

gnuplot <<EOF
set term png size 1000,1000;
set output "out.png";
func1(x) = x / 2
func2(x) = x * 2
plot "test.dat" u (func1(column(1))):(func2(column(2))) ls 1 smooth csplines;
EOF

answered Jul 13, 2016 at 5:08

Christoph

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2 Comments

Joce Over a year ago

Alternatively, escape the $ signs with a `\`.

Christoph Over a year ago

@Joce Yes, but I prefer using column whenever the script is created automatically, because that always works regardless of how you invoke gnuplot or prepare the script.

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