regex - Complete word matching using grepl in R

Question

Consider the following example:

> testLines <- c("I don't want to match this","This is what I want to match")
> grepl('is',testLines)
> [1] TRUE TRUE

What I want, though, is to only match 'is' when it stands alone as a single word. From reading a bit of perl documentation, it seemed that the way to do this is with , an anchor that can be used to identify what comes before and after the patter, i.e. word matches 'word' but not 'sword'. So I tried the following example, with use of Perl syntax set to 'TRUE':

> grepl('is',testLines,perl=TRUE)
> [1] FALSE FALSE

The output I'm looking for is FALSE TRUE.

Answer 1

"<" is another escape sequence for the beginning of a word, and ">" is the end. In R strings you need to double the backslashes, so:

> grepl("\<is\>", c("this", "who is it?", "is it?", "it is!", "iso"))
[1] FALSE  TRUE  TRUE  TRUE FALSE

Note that this matches "is!" but not "iso".