如果我们有一个长字符串，那么我们可能想提取位于两个字符串之间的一部分字符串。例如，如果我们有一个字符串“ E-learning改变世界上的教育系统”，而我们想勇敢地提取字符串“教育系统”，那么我们必须非常小心地将字符串传递给字符串函数，您将在示例中知道这一点。使用gsub函数提取并不困难，但是我们必须确保使用正确的语法，否则结果将令人讨厌。
x1<-"E-learning changing the education system in the world"
gsub(".*changing (.+) in.*", "\\1",x1)
[1] "the education system"
gsub(".*the (.+) system.*", "\\1",x1)
[1] "education"
x2<-"Nhooo helping programmers around the world"
gsub(".*helping (.+) around.*", "\\1",x2)
[1] "programmers"
gsub(".*Nhooo (.+) programmers.*", "\\1",x2)
[1] "helping"
gsub(".*helping (.+) the.*", "\\1",x2)
[1] "programmers around"
x3<-"kindness is a mark of faith, and whoever has not kindness has not faith"
gsub(".*a (.+) of.*", "\\1",x3)
[1] "mark"
gsub(".*and (.+) has.*", "\\1",x3)
[1] "whoever has not kindness"
gsub(".*has (.+) has.*", "\\1",x3)
[1] "not kindness"
gsub(".*has (.+) faith.*", "\\1",x3)
[1] "not"
gsub(".*and (.+) faith.*", "\\1",x3)
[1] "whoever has not kindness has not"
gsub(".*of (.+) whoever.*", "\\1",x3)
[1] "faith, and"
gsub(".*of (.+) and.*", "\\1",x3)
[1] "faith,"
x4<-"直到他为他的兄弟希望他自己的一切之前，你们中没有人真正相信。"
gsub(".*of (.+) truly.*", "\\1",x4)
[1] "you"
gsub(".*believes (.+) until.*", "\\1",x4)
[1] "直到他为他的兄弟希望他自己的一切之前，你们中没有人真正相信。"
gsub(".*believes (.+) for.*", "\\1",x4)
[1] "until he wishes for his brother what he wishes"
gsub(".*you (.+) until.*", "\\1",x4)
[1] "truly believes"
gsub(".*his (.+) what.*", "\\1",x4)
[1] "brother"
gsub(".*he (.+) for.*", "\\1",x4)
[1] "wishes"
gsub(".*until (.+) for.*", "\\1",x4)
[1] "he wishes for his brother what he wishes"
gsub(".*truly (.+) until.*", "\\1",x4)
[1] "believes"
gsub(".*truly (.+) what.*", "\\1",x4)
[1] "believes until he wishes for his brother"
gsub(".*truly (.+) for.*", "\\1",x4)
[1] "believes until he wishes for his brother what he wishes"
gsub(".*until (.+) what.*", "\\1",x4)
[1] "he wishes for his brother"
x5<-"To overcome evil with good is good, to resist evil by evil is evil."
gsub(".*To (.+) with.*", "\\1",x5)
[1] "overcome evil"
gsub(".*good (.+) good.*", "\\1",x5)
[1] "is"
gsub(".*resist (.+) evil.*", "\\1",x5)
[1] "evil by evil is"
gsub(".*to (.+) evil.*", "\\1",x5)
[1] "resist evil by evil is"
gsub(".*evil (.+) evil.*", "\\1",x5)
[1] "is"
gsub(".*To (.+) evil.*", "\\1",x5)
[1] "overcome evil with good is good, to resist evil by evil is"
gsub(".*good, (.+) resist.*", "\\1",x5)
[1] "to"
gsub(".with (.+) is.*", "\\1",x5)
[1] "To overcome evilgood is good, to resist evil by evil"