Replacing white space with one single backslash

问题:

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

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

I found how to replace with multiple backslashes but wasn't able to adapt it to a single backslash.

I tried this so far:

x <- "foo bar" 
gsub(" ", "\\ ", x)
# [1] "foo bar"

gsub(" ", "\\\ ", x)
# [1] "foo bar"

gsub(" ", "\\\\ ", x)
# [1] "foo\\ bar"

However, all the outcomes do not satisfy my needs. I need the replacement to dynamically create file paths which contain folders with names like

/some/path/foo bar/foobar.txt.

To use them for shell commands in system() white spaces have to be exited with a \ to

/some/path/foo\ bar/foobar.txt.

Do you know how to solve this one?

回答1:

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.)

回答2:

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.