Replacing white space with one single backslash

Question

I want to replace a white space with ONE backslash and a whitespace like this:

\"foo bar\" --> \"foo\\ bar\"

I found how to replace wit

Answer 1

To replace a space with one backslash and a space, you do not even need to use regular expression, use your gsub(" ", "\\ ", x) first attempt with fixed=TRUE:

> x <- "foo bar" 
> res <- gsub(" ", "\\ ", x, fixed=TRUE)
> cat(res, "\n")
foo\ bar 

See an online R demo

The cat function displays the "real", literal backslashes.

Answer 2

Your problem is a confusion between the content of a string and its representation. When you print out a string in the ordinary way in R you will never see a single backslash (unless it's denoting a special character, e.g. print("y\n"). If you use cat() instead, you'll see only a single backslash.

x <- "foo bar"
y <- gsub(" ", "\\\\ ", x)
print(y)
## [1] "foo\\ bar"
cat(y,"\n")  ## string followed by a newline
## foo\ bar

There are 8 characters in the string; 6 letters, one space, and the backslash.

nchar(y)  ## 8

For comparison, consider \n (newline character).

z <- gsub(" ", "\n ", x)
print(z)
## [1] "foo\n bar"
cat(z,"\n")
## foo
##  bar 
nchar(z)  ## 8

If you're constructing file paths, it might be easier to use forward slashes instead - forward slashes work as file separators in R on all operating systems (even Windows). Or check out file.path(). (Without knowing exactly what you're trying to do, I can't say more.)