| shQuote {base} | R Documentation |
Quote a string to be passed to an operating system shell.
shQuote(string, type = c("sh", "csh", "cmd", "cmd2"))
string |
a character vector, usually of length one. |
type |
character: the type of shell quoting. Partial matching is
supported. |
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 bash, ksh and
zsh.
The other type of quoting is for the C-shell (csh and
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.
In Windows, command line interpretation is done by the application
as well as the shell. It may depend on the compiler used:
Microsoft's rules for the C run-time are given at
https://msdn.microsoft.com/library/ms880421. It may depend on
the whim of the programmer of the application: check its
documentation. The type = "cmd" quoting surrounds the string
by double quotes and escapes internal double quotes by a backslash.
As Windows path names cannot contain double quotes, this makes
shQuote safe for use with many applications when used with
system or system2. The Windows
cmd.exe shell (used by default with shell)
uses type = "cmd2" quoting: special characters are prefixed
with "^". In some cases, two types of quoting should be
used: first for the application, and then type = "cmd2"
for cmd.exe. See the examples below.
Loukides, M. et al (2002) Unix Power Tools Third Edition. O'Reilly. Section 27.12.
Discussion in PR#16636.
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, assuming cmd.exe:
perlcmd <- 'print "Hello World\\n";'
## Not run:
shell(shQuote(paste("perl -e",
shQuote(perlcmd, type = "cmd")),
type = "cmd2"))
## End(Not run)