grep with $ in string

Question

In R How do I grep something which has a $ in string. In This below example I need to grep string "NB6106$MU-MU.rma"

x<-c("NB6106$MU-MU.rma", "NB610634$MU-MU.rma")

x[grep(pattern="*6106$*.rma", x = x)] #does not work

Answer 1

You may use

x<-c("NB6106$MU-MU.rma", "NB610634$MU-MU.rma")
x[grep(pattern="6106\\$.*\\.rma", x = x)]

See the R demo

Details

• 6106\\\\$ - 6106$ substring
• .* - any 0+ chars
• \\\\.rma - a .rma substring

If you plan to make sure you do not grep 11116106$...rma , you may use

"(^|\\D)6106\\$.*\\.rma$"

where (^|\\\\D) matches start of string ( ^ ) or ( | ) a non-digit char ( \\D ), and $ at the end ensure the end of string appears right after .rma .

Answer 2

You need to escape it. $ by itself in a regular expression indicates the end of the string, so you need to tell R that here you mean it literally as a $, which is done by escaping. The escape character is \\ . So, in theory, you'll type in \\$ . BUT, since you're writing the pattern as a literal string (within quotes), you ALSO need to escape the escape character, so that R knows to transfer it literally to the regex interpretor. Hence: \\\\$ .

Other issues with your code: * doesn't mean "any characters". It means "repeat the previous character zero or more times". . means any character, and .* means any number of any character, which is what you're looking for. And of course, if you want a literal period, you need to escape that too: \\\\.