name <- c('john','carl', 'hank')
salary <- c('$23,456.33','$45,677.43','$76,234.88')
emp_data <- data.frame(name,salary)

clean <- function(ttt){
as.numeric(gsub('[^a-zA-z0-9.]','', ttt))
}
sapply(emp_data, clean)

library(dplyr)
library(stringr)

emp_data %>%
  mutate_if(~any(str_detect(., '^\$')),
            ~as.numeric(str_replace_all(., '[$,]', '')))

doll_cols <- sapply(emp_data, function(x) any(startsWith(as.character(x), '$')))
emp_data[doll_cols] <- lapply(emp_data[doll_cols],
                              function(x) as.numeric(gsub('\$|,', '', x)))