The columnhead(x) function may only be used as part of a plot, splot,
or stats command. It evaluates to a string containing the content of
column x in the first line of a data file. This is typically used to
extract the column header for use in a plot title.
See plot datafile using (p. ![[*]](crossref.png)
).
Example:
set datafile columnheader
plot for [i=2:4] DATA using 1:i title columnhead(i)
