sysuse auto, clear

foreach var of varlist rep78{
count if !missing(`var')
bys `var': gen frac = _N/r(N)
gsort -frac
levelsof `var' if frac>.20

local wc: word count `r(levels)'
local plabel ""

forvalues i=1/`wc'{
local plabel "`plabel' plabel(`i' name)"
}

graph pie, over(`var') `plabel' sort descending ///
legend(row(1) pos(6) rowgap(*0.3) region(lcolor(none)))

}


请问这个绘制饼图的命令中`var'这是什么意思，var前后的两个符合表示什么？