char <- "a"
is_upper <- grepl("[[:upper:]]", char)
is_lower <- grepl("[[:lower:]]", char)
# is_upper = FALSE
# is_lower = TRUE
# Works beyond ASCII
cyrillic <- "Ж"
cyrillic_upper <- grepl("[[:upper:]]", cyrillic)
# cyrillic_upper = TRUE
# No case: both are FALSE
digit <- "1"
is_upper_digit <- grepl("[[:upper:]]", digit)
is_lower_digit <- grepl("[[:lower:]]", digit)
# is_upper_digit = FALSE
# is_lower_digit = FALSE
cat("is_upper =", is_upper, "\n")
cat("is_lower =", is_lower, "\n")
cat("cyrillic_upper =", cyrillic_upper, "\n")
cat("is_upper_digit =", is_upper_digit, "\n")
cat("is_lower_digit =", is_lower_digit, "\n")