gsub + backslashes

On Mon, 24 Apr 2006, Torsten Hothorn wrote:

Dear developeRs,

I thought that backslashes can be escaped in the usual way (and I think I
did this before) but I can't see why

R> gsub("\\", "x", "\alpha")
Error in gsub(pattern, replacement, x, ignore.case, extended, fixed,
useBytes) :
        invalid regular expression '\'

gives an error. Or am I just blind?

Escape for R and escape for regexp:

gsub("\\\\", "x", "\\alpha")

[1] "xalpha"

Also, unless fixed==TRUE, you need to double the backslash
in the replacement string (because \\<digit|U|L> has a special
meaning when fixed!=TRUE):

   > cat(gsub("/", "\\\\", "C:/Program Files/R"),"\n")
   C:\Program Files\R
   > cat(gsub("/", "\\", "C:/Program Files/R", fixed=T), "\n")
   C:\Program Files\R

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