我对正则表达式很陌生，我正在尝试捕获两个字符串之间的文本。但如果字符串不存在，我想捕获所有文本。
这是一个例子：
报告 #1：观察结果：一只猫在伸展。结论：这只猫很灵活。
我可以使用以下代码来捕获“观察”和“结论”之间的文本：
(?:(?i)observations)(.*)(?:(?i)conclusions)
但如果另一个文字写着：
报告 #1：观察结果：一只猫在伸展。这只猫很灵活。
我想在“Observations”之后捕获所有内容。
或者如果起始字符串“Observations”不存在：
报告 #1：一只猫在伸展。结论：这只猫很灵活。
我想从头到尾捕获字符串“结论”。
我猜条件正则表达式可能会有所帮助？
谢谢！
【问题讨论】：
单行：
ex <- c(
"Report #1: Observations: A cat is stretching. Conclusions: This cat is flexible.",
"Report #1: Observations: A cat is stretching. This cat is flexible.",
"Report #1: A cat is stretching. Conclusions: This cat is flexible."
)
gsub("(^.*observations|conclusions.*$)", "", ex, ignore.case = TRUE)
# [1] ": A cat is stretching. "
# [2] ": A cat is stretching. This cat is flexible."
# [3] "Report #1: A cat is stretching. "
您可能需要边界或 G5W 建议的单词之前/之后的空格。单词边界看起来像这样，给定示例文本的输出相同：
gsub("(^.*\\bobservations\\b|\\bconclusions\\b.*$)", "", ex, ignore.case = TRUE)
【讨论】：
一种方法是使用两个正则表达式：
reports = c(
"Report #1: Observations: A cat is stretching. Conclusions: This cat is flexible.",
"Report #1: Observations: A cat is stretching. This cat is flexible.")
reports = sub(".*Observations:\\s*", "", reports)
reports = sub("\\s*Conclusions:.*", "", reports)
reports
[1] "A cat is stretching."
[2] "A cat is stretching. This cat is flexible."
【讨论】：
\\b。