using regular expression in list.files of R function

Question

I want to use list.files of R to list files containing this pattern "un[a digit]" such as filename_un1.txt, filename_un2.txt etc... Here is the general code:

list_files <- list.files(path="my_file_path", recursive = TRUE, pattern = "here I need help", full.names = TRUE)

I have tried putting un\\d in the pattern input but does not work.

Answer 1

You should bear in mind that in R, strings allow using escape sequences. However, the regex engine needs a literal \\ to pass shorthand character classes (like \\d for digits) or to escape special chars (like \\\\. to match a literal dot.)

So, you need

pattern = "_un\\d+\\.txt$"

where

• _un - matches a literal substring _un
• \\\\d+ - matches 1 or more digits (as + is a one or more quantifier)
• \\\\. - matches a literal dot
• txt - matches a literal sequence of characters txt
• $ - end of string.

Answer 2

list_files <- list.files(path="my_file_path", recursive = TRUE, pattern = "un[0-9]", full.names = TRUE)