空行的正則表達式是什么？

Question

http://www.endmemo.com/program/R/grep.php

我已經在圖表中查看了與空白行相對應的正則表達式，但似乎找不到它。 我已經嘗試過\\\\n但這意味着要換行，而不一定是空白。

例如 ：

string = c("Precedence: bulk", 
  "List-Unsubscribe: <mailto:zzzzteana-unsubscribe@yahoogroups.com>", 
  "Content-Transfer-Encoding: 7bit", 
  "", 
  "Martin A posted:", 
  "Tassos Papadopoulos, the Greek sculptor behind the plan, judged that the", 
  " Mount Athos monastic community, was ideal for the patriotic sculpture. ", 
  " ", 
  " As well as Alexander's granite features, 240 ft high and 170 ft wide, a",
  "planned", 
  "---------------------", 
  "So is this mountain limestone or granite?")

因此，第4行和第8行為空，我希望grep返回這些索引。

Answer 1

在R中，您需要轉義反斜杠，所以它應該是^\\\\s*$ 。 您也可以使用^[[:space:]]*$ 。

grepl("^[[:space:]]*$", c("", "  ", "\t"))
# [1] TRUE TRUE TRUE
grep("^[[:space:]]*$", string)
# [1] 4 8