Quote Strings for Use in OS Shells
Quote a string to be passed to an operating system shell.
shQuote(string, type = c("sh", "csh", "cmd"))
- a character vector, usually of length one.
- character: the type of shell. Partial matching is
"cmd"refers to the Windows NT shell, and is the default under Windows.
The default type of quoting supported under Unix-alikes is that for
the Bourne shell
sh. If the string does not contain single
quotes, we can just surround it with single quotes. Otherwise, the
string is surrounded in double quotes, which suppresses all special
meanings of metacharacters except dollar, backquote and backslash, so
these (and of course double quote) are preceded by backslash. This
type of quoting is also appropriate for
The other type of quoting is for the C-shell (
tcsh). Once again, if the string does not contain single
quotes, we can just surround it with single quotes. If it does
contain single quotes, we can use double quotes provided it does not
contain dollar or backquote (and we need to escape backslash,
exclamation mark and double quote). As a last resort, we need to
split the string into pieces not containing single quotes and surround
each with single quotes, and the single quotes with double quotes.
The Windows shell supports only double quoting. All this
implementation does is to surround the string by double quotes and
escape internal double quotes by a backslash. As Windows path names
cannot contain double quotes, this makes
shQuote safe for use
with file paths in
system, and with
if the default shell is used.
It will usually be safe to use
shQuote to quote arguments of a
command, but because
system does not use a shell,
interpretation of quoted arguments is done by the run-time code of the
executable. This may depend on the compiler used: Microsoft's rules
for the C run-time are given at
Loukides, M. et al (2002) Unix Power Tools Third Edition. O'Reilly. Section 27.12.
Quotes for quoting R code.
sQuote for quoting English text.
test <- "abc$def`gh`i\\j" cat(shQuote(test), "\n") ## Not run: system(paste("echo", shQuote(test))) test <- "don't do it!" cat(shQuote(test), "\n") tryit <- paste("use the", sQuote("-c"), "switch\nlike this") cat(shQuote(tryit), "\n") ## Not run: system(paste("echo", shQuote(tryit))) cat(shQuote(tryit, type = "csh"), "\n") ## Windows-only example. perlcmd <- 'print "Hello World\n";' ## Not run: shell(paste("perl -e", shQuote(perlcmd, type = "cmd")))