Sys.getenv
Get Environment Variables
Description
Returns the values of environment variables.
Usage
Sys.getenv(x = NULL, unset = "", names = NA)
Arguments
x |
a vector of character strings giving the names of the environment
variables whose values are sought.
In UNIX, by convention, environment variable names are specified using
upper-case letters. In Windows, environment variable names are
case-insensitive. If x is missing, the entire environment
is returned.
|
unset |
a character string. Displayed when the request contains an environment
name that is not set. By default, "".
|
names |
a logical value or NA.
- If TRUE, the names attribute is included in the return value.
- If FALSE, the names attribute is excluded from the return value.
- If NA (the default), the names attribute is included in the return value when
x is missing, or if there is more than one element in x.
Otherwise, the names attribute is excluded from the return value.
|
Value
returns a vector of character strings giving the values of the
environment variables named in x, or the values of all
environment variables if x is omitted. If an element
of x is not the name of an environment variable, the
corresponding element of the returned vector is the
null string ("") by default.
Depending on the value of the names argument, the returned vector either has or does not
have a names attribute that holds the variable names.
Background
the engine uses several environment variables, such as those in the
example section.
This function can be used to retrieve the value of any environment variable,
not just those set by the engine.
The Sys.getenv function replaces getenv, which was used
in S-PLUS and R.
Examples
Sys.getenv("HOME")
Sys.getenv("S_PRINT_ORIENTATION") # might return "landscape" (on Unix)
shome <- "SHOME"
# returns character string of the home directory
Sys.getenv(shome)
all.env <- Sys.getenv() # whole environment
leading.S <- grep("^S", names(all.env))
# index into all.env for those names starting with 'S'
all.env[leading.S]
# values of these variables; names are preserved
Sys.getenv(c("SHOME", "S_FIRST"))
Sys.getenv()[c("SHOME", "S_FIRST")]
Sys.getenv("a", unset = "not set")
#
# "not set"
Sys.getenv(names = FALSE) # list all environment variables without names.
Sys.getenv("HOME") # no names attribute
Sys.getenv(c("HOME", "FOO")) # with names attribute