GNU plot conditional plotting

($1 <=3  ? $2 : 1/0)

It means “if the current number in the first column ($1) is less than 3, use the second column ($2), otherwise draw nothing”.

plot the first two columns only when the third one equals zero. Then you can try this:

plot '1.dat' using 1:($3==0?$2:1/0)

GNU plot lengend(key) too wide

In GNU plot, some times the legend is too wide, leave a lot unused space herizontally.

set key width -5

or something like that.

Perl my function

In Perl,
my function define a local variable.

my $A = "what ever"

lowcut

Low frequency cut