Merge Multiple spaces to single space; remove trailing/leading spaces

Or simply try the squish function from stringr

library(stringr)
string <- "  Hi buddy   what's up   Bro "
str_squish(string)
# [1] "Hi buddy what's up Bro"

You do not need to import external libraries to perform such a task:

string <- " Hi        buddy        what's up    Bro "
string <- gsub("\\s+", " ", string)
string <- trimws(string)
string
[1] "Hi buddy what's up Bro"

Or, in one line:

string <- trimws(gsub("\\s+", " ", string))

Much cleaner.

Another approach using a single regex:

gsub("(?<=[\\s])\\s*|^\\s+|\\s+$", "", string, perl=TRUE)

Explanation (from)

NODE                     EXPLANATION
--------------------------------------------------------------------------------
  (?<=                     look behind to see if there is:
--------------------------------------------------------------------------------
    [\s]                     any character of: whitespace (\n, \r,
                             \t, \f, and " ")
--------------------------------------------------------------------------------
  )                        end of look-behind
--------------------------------------------------------------------------------
  \s*                      whitespace (\n, \r, \t, \f, and " ") (0 or
                           more times (matching the most amount
                           possible))
--------------------------------------------------------------------------------
 |                        OR
--------------------------------------------------------------------------------
  ^                        the beginning of the string
--------------------------------------------------------------------------------
  \s+                      whitespace (\n, \r, \t, \f, and " ") (1 or
                           more times (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  $                        before an optional \n, and the end of the
                           string

This seems to meet your needs.

string <- "  Hi buddy   what's up   Bro "
library(stringr)
str_replace(gsub("\\s+", " ", str_trim(string)), "B", "b")
# [1] "Hi buddy what's up bro"