Q:

R, check if special character in string

How to use R to check if a string contains at least one of the following characters, /\:*?"<>|. Also, I hope the string can contain any other characters, e.g. -.
Actually these characters are the ones not allowed for windows directory (folder) name.

A:

Define the pattern(s) you want to find in the string, then use grepl to find them
pattern <- "/|:|\\?|<|>|\\|\\\\|\\*"

myStrings <- c("this/isastring", "this*isanotherstring", "athirdstring")

grepl(pattern, myStrings)
# [1] TRUE TRUE FALSE

A break down of pattern:
if it were
pattern <- "/"

This would just search for "/"
The vertical bar/pipe is used as an 'OR' condition on the pattern, so 
pattern <- "/|:"

is searching for either "/" OR "|"
To search for the "|" character itself, you need to escape it using "\"
pattern <- "/|:|\\|"

And to search for the "\" character, you need to escape that too (and similarly for other special characters, ?, *, ...
pattern <- "/|:|\\?|<|>|\\|\\\\"

Reference: 
Dealing with special characters in R

