A complete but simplest code in Awk doing least squares fitting. I didn’t write the original code, this kind of code can be found in the text books and from the internet search results.
BEGIN{
sumx = 0;
sumy = 0;
sumxx = 0;
sumxy = 0;
}{
x[NR] = $1;
y[NR] = $2;
sumx += x[NR];
sumy += y[NR];
sumxx += x[NR]*x[NR];
sumxy += x[NR]*y[NR];
}END{
det = NR*sumxx - sumx*sumx;
a = (NR*sumxy - sumx*sumy)/det;
b = (-sumx*sumxy+sumxx*sumy)/det;
for(i=1;i<=NR;i++) newdet+=(y[i]-a*x[i]+b)^2;
printf("%.16f %.16f\n",a,newdet);
}