points data frame
  x y
1 1 1
2 2 3
3 3 2
4 4 4

Call:
lm(formula = y ~ x, data = points)

Residuals:
   1    2    3    4 
-0.3  0.9 -0.9  0.3 

Coefficients:
            Estimate Std. Error t value Pr(>|t|)
(Intercept)   0.5000     1.1619   0.430    0.709
x             0.8000     0.4243   1.886    0.200

Residual standard error: 0.9487 on 2 degrees of freedom
Multiple R-squared:  0.64,      Adjusted R-squared:  0.46 
F-statistic: 3.556 on 1 and 2 DF,  p-value: 0.2 

newpoints data frame
  x y
1 1 1
2 2 3
3 3 2
4 4 4
Predicted values and prediction interval.
  fit       lwr      upr
1 0.9 -4.944327 6.744327
2 2.5 -2.063652 7.063652
3 3.9 -1.670648 9.470648