使用 OS 特定的换行符（CRLF、LF、CR）构建字符串以将其写入数据库 table 列

Question

我想将包含 R (\n) 的常用换行符的字符串写入数据库的列 table。

如何将新行转换为操作系统特定的表示形式（Windows = CR/LF、Linux = LF、Mac = CR...）？

我了解到 R 不提供操作系统特定的表示，所以我必须找到一个解决方法：

Printing newlines with print() in R

对 print/cat 字符串的任何尝试都失败了：

msg <- "I want to have \n a new line"
cat(msg)
# I want to have 
#  a new line

out <- capture.output(cat(msg))
out
# a vector with two elements (one for each row but no new line characters anymore)
# [1] "I want to have " " a new line"

paste(out, collapse = "\n")   # how could I inject the correct new line characters here?
# [1] "I want to have \n a new line"

# welcome endless-loop :-)

有没有办法让 R 从字符串中的 \n 创建正确的换行符？

PS：我正在使用内置的 tcltk 包和 puts 但我总是以 R "reconverting" 换行符结尾 \n... 另一个 "cheat" 可能是用引号将 \n 括起来，以便将其视为一行。到目前为止我不知道这是怎么回事...

Answer 1

在R中正确设置新行代码的一种方法是查询操作系统。由于 OS X 和 Linux 的行为方式相同，因此这是一个判断操作系统是否为 Windows 的问题。一种方法是查询 OS 环境变量，如下所示。

if(substr(Sys.getenv("OS"),1,7) == "Windows") {
    # set Windows newline
  newLine <- "\r\n"
}
else {
    # set non-Windows newline
    newLine <- "\n"
}

接下来使用 paste() 和 newLine 对象来为操作系统的新行生成正确的字符。

paste("my text string on a line",newline,sep="")

问候，

莱恩

Answer 2

在这里您可以找到我的最终实现，作为已接受答案的可能替代方案：

# Returns the operating system specific new line character(s):
# CR LF on Windows, else only LF...
# Simlar to Microsofts .Net "Environment.NewLine"
platform.NewLine <- function() {

  is.windows <- grepl(tolower(.Platform$OS.type), "windows", fixed = TRUE)

  if (is.windows) {
    newline <- "\r\n"
  } else {
    newline <- "\n"
  }

  sys.name <- Sys.info()["sysname"]
  is.windows.2nd.opinion <- grepl(tolower(sys.name), "windows", fixed = TRUE)

  if (is.windows != is.windows.2nd.opinion)
    warning("R seems to run on Windows OS but this could not be recognized for sure")

  return(newline)
}

# Usage (examples) ------------------------------------------------------------------------------------------------

newline <- platform.NewLine()

# "print" shows the "symbolic" names (escape codes)
print(paste("Line1", "Line2", sep = newline))
# [1] "Line1\r\nLine2"
# uses "\n" or "\r\n" depending on your OS

# "cat" applies the newline escape codes to the output
cat(paste("Line1", "Line2", sep = newline))
# Line1
# Line2

使用 OS 特定的换行符（CRLF、LF、CR）构建字符串以将其写入数据库 table 列

Build string with OS-specific newline characters (CRLF, LF, CR) to write it into a database table column

newline

r

lf