sub function in R Language is used to replace the first match of a pattern in a string. If there is a vector of string elements, then it will replace the first match of the pattern from all elements.

Syntax: sub(pattern, replacement, string, ignore.case=TRUE/FALSE)

Parameters:
pattern: string to be matched
replacement: string for replacement
string: String or String vector
ignore.case: Boolean value for case-sensitive replacement

Example 1:

# R program to illustrate
# the use of sub() function

# Create a string
x <- "Geeksforgeeks"

# Calling sub() function
sub("eek", "ood", x)

# Calling sub() with case-sensitivity
sub("gee", "Boo", x, ignore.case = FALSE)

# Calling sub() with case-insensitivity
sub("gee", "Boo", x, ignore.case = TRUE)

Output:

[1] "Goodsforgeeks"
[1] "GeeksforBooks"
[1] "Booksforgeeks"

Example 2:

# R program to illustrate
# the use of sub() function

# Create a string
x <- c("Geekforgeek", "Geeksforgeeks", "geeksforGeeks")

# Calling sub() function
sub("Gee", "boo", x)

# Calling sub() with case-insensitivity
sub("Gee", "boo", x, ignore.case = TRUE)

Output:

[1] "bookforgeek"   "booksforgeeks" "geeksforbooks"
[1] "bookforgeek"   "booksforgeeks" "booksforGeeks"