shQuote: Quote Strings for Use in OS Shells

Description

Quote a string to be passed to an operating system shell.

Usage

shQuote(string, type = c("sh", "csh", "cmd"))

Arguments

string

a character vector, usually of length one.

type

character: the type of shell. Partial matching is supported. "cmd" refers to the Windows NT shell, and is the default under Windows.

Details

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.

windows 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 shell 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 http://msdn2.microsoft.com/en-us/library/ms880421.aspx.

References

Loukides, M. et al (2002) Unix Power Tools Third Edition. O'Reilly. Section 27.12.

Examples

Run this code

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")))