Replacing entire string when a single word is in the string R -

I was thinking that someone has come to the R while cleaning the data to solve this problem. For example, list of strings:

  strings = c ("Hello World", "Goodbye all", "Help is appreciated", "Hello Sam")  < / Pre> 
 Then we can go through the list of strings and whenever a certain word is found, the whole string will be changed. 
 
 So if we are searching for the word "hello" then it will be "mathematics" 
 
 then I will see that it will be produced: 
 
  "          P> 
 
 Just use  grepl : 
 
  wire = c ("hello world "," Goodbye all "," Help is appreciated "," Hello Sam ") Wire [gripple ("hello", strings)] & lt; - "Mathematics" & gt; String [1] "Mathematics" "Goodbye All" "Help is appreciated" "Mathematics"