amin.R

lm_eqn <- function(model){

  mod_frame <- broom::tidy(model)

  eqn_string <- sprintf("The response is equal to %.2f ", mod_frame$estimate[1])

  model_terms <- function(i){
    if(i == 1){return(".")}
    paste(sprintf("+ %.2f %s", mod_frame$estimate[i], mod_frame$term[i]), model_terms(i - 1))
  }
  
  eqn_string <- paste(eqn_string, model_terms(nrow(mod_frame)))

  print(eqn_string)

}

lmod <- lm(mpg ~ cyl + hp + disp, data = mtcars)

lm_eqn(lmod)

Actually, the code below is better since it adds the variables that have (NA) values in their coef.

lm_eqn <- function(model){
  b <- coef(model)
  names(b)[1] <- ""  
  eqn <- paste(format(b, digits=1), names(b), collapse=" + ")
    rsq <- format(summary(model)$r.squared, digits=3)
    cat("The response is equal to", eqn, ", R2 =", rsq, "\n")
    invisible(model)
}

lmod <- lm(uptake ~ Plant + Treatment + conc, data = CO2)
lm_eqn(lmod)