R 如何获取当前控制台输出的内容或长度？

我正在寻找下面的函数get_output_content或至少get_output_length，这将告诉我控制台中打印了多少字符

test <- function(){
   cat("ab")
   cat("\b")
   cat("cd")
   c <- get_output_content() # "acd" (I'd be happy with "ab\bcd" as well)
   l <- get_output_length()  # 3
   return(list(c,l))
}
test()

test类似这样的（？）

test
nchar（capture.output（cat）（“ab\bcd”））
？或者
sink（）
在这里可能更方便。我想我可以把它沉到某个地方，计算我需要计算的数量，然后在控制台上取消墨水并重新打印，在每次迭代中都会这样做，但这会带来很大的开销！
library(pbapply)
my_files <- paste0(1000:1,".pdf")
work_on_pdf <- function(pdf_file){
  Sys.sleep(0.001)
}
report <- pbsapply(my_files,work_on_pdf) # the simple version, but I want to add the pdf name next to the bar to have more info about my progress
# so I tried this but it's not satisfying because it "eats" some of the current output of pbapply
report <- pbsapply(my_files,function(x){
    buffer_length <- 25
    work_on_pdf(x)
    catmsg <- paste0(c( # my additional message, which is in 3 parts: 
      rep("\b",buffer_length),          # (1) eat 25 characters
      x,                                # (2) print filename
      rep(" ",buffer_length-nchar(x))), # (3) print spaces to cover up what may have been printed before
      collapse="")
    cat(catmsg)
  })

library(pbapply)
my_files <- paste0(1000:1,".pdf")
work_on_pdf <- function(pdf_file){
  Sys.sleep(0.01)
}
pbsapply2 <- function(X,FUN,FUN2){
  # FUN2 will give the additional message  
  pbsapply(X,function(x){
    msg <- FUN2(x)
    cat(msg)
    output <- FUN(x)
    eraser <- paste0(c(  
      rep("\b",nchar(msg)),  # go back to position before additional message
      rep(" ",nchar(msg)),   # cover with blank spaces         
      rep("\b",nchar(msg))), # go back again to initial position
      collapse="")
    cat(eraser)
    return(output)
  })    
}
report <- pbsapply2(my_files,work_on_pdf,function(x) paste("filename:",x))

test <- function(){
  c <- paste0(capture.output(cat("ab")),
              capture.output(cat("\b")),
              capture.output(cat("cd")))
  n <- nchar(c)
  l <- length(c)
  return(list(c,n,l))
}
test()