capture part of value of filename that caused error using basename

Question

I'm on a windows box, and I'm using basename to extract file names from some directories. Apparently, there is a limit to the size that a file name can be, otherwise basename throws an error (earlier I was on a linux and there I don't remember a [roblem, and from a quick glance at the source code it looks like basename is different for different systems - so this is quite likely not a reproducible example on linux or osx).

Anyway, I am wrapping basename in a tryCatch and would like to just capture the last chunk of the filename when there is an error. How can I do this?

Example to follow:

filename <- paste0("c:/some directory/", paste(rep("abc ", 100), collapse=""), ".txt")
basename(filename)
# Error in basename(filename) : path too long

So, I do a tryCatch,

value <- tryCatch(basename(filename), error=function(e) e)
str(value)
# $ message: chr "path too long"
# $ call   : language basename(filename)
# - attr(*, "class")= chr [1:3] "simpleError" "error" "condition"

But, how could I get, say just the last 30 characters of the filename, instead of just an error message?

Answer 1

Better math here than in the comment. I don't get an error like you said, so I will make one

filename <- paste0("c:/some directory/", paste(rep("abc ", 100), collapse=""), ".txt")
basename(filename)


value <- tryCatch(simpleError(), error=function(e)
  substring(filename, nchar(filename) - 29, nchar(filename)))
str(value)

# chr "c abc abc abc abc abc abc .txt"

or

value <- tryCatch(simpleError(), error=function(e)
  gsub('(.{30}$)|.', '\\1', filename))
str(value)

# chr "c abc abc abc abc abc abc .txt"