library {base} | R Documentation

## Loading and Listing of Packages

### Description

`library` and `require` load add-on packages; `provide` allows code to register services that packages provide. `.First.lib` is called when a package is loaded; `.packages` returns information about package availability. `.path.package` returns information about where a package was loaded from.

### Usage

    library(package, help = NULL, lib.loc = .lib.loc,
            character.only = FALSE, logical.return = FALSE,
            warn.conflicts = TRUE, keep.source = getOption("keep.source.pkgs"))
    require(package, quietly = FALSE, warn.conflicts = TRUE,
            keep.source = getOption("keep.source.pkgs"))

    .First.lib(libname, pkgname)
    .Last.lib(libpath)

    .packages(all.available = FALSE, lib.loc = .lib.loc)
    .path.package(package = .packages())
    .lib.loc
    .Library
    .Autoloaded

### Arguments

`package, help` | `name` or character string giving the name of a package.
`lib.loc` | a character vector describing the location of R library trees to search through.
`character.only` | a logical indicating whether `package` or `help` can be assumed to be character strings.
`logical.return` | logical. If it is `TRUE`, `FALSE` or `TRUE` is returned to indicate success.
`warn.conflicts` | logical. If `TRUE`, warnings are printed about `conflicts` from attaching the new package, unless that package contains an object `.conflicts.OK`.
`keep.source` | logical. If `TRUE`, functions ``keep their source'' including comments, see `options(keep.source = *)`.
`quietly` | a logical. If `TRUE`, a warning will not be printed if the package cannot be found.
`libname` | a character string giving the library directory where the package was found.
`pkgname` | a character string giving the name of the package.
`libpath` | a character string giving the complete path to the package.
`all.available` | logical; if `TRUE` return `character` vector of all available packages in `lib.loc`.

### Details

`library(package)` and `require(package)` both load the package with name `package`. `require` is designed for use inside other functions; it returns `FALSE` and optionally gives a warning, rather than giving an error, if the package does not exist. Both functions check and update the list of currently loaded packages and do not reload code that is already loaded.

For large packages, setting `keep.source = FALSE` may save quite a bit of memory.

If `library` is called with no `package` or `help` argument, it gives a list of all available packages in `lib.loc` and invisibly returns their names (same as `.packages(all = TRUE)`).

`library(help = somename)` prints information on the package `somename`, typically by listing the most important user level objects it contains.

`.First.lib` is called when a package is loaded by `library`. It is called with two arguments, the name of the library directory where the package was found (i.e., the corresponding element of `lib.loc`), and the name of the package (in that order). It is a good place to put calls to `library.dynam()` which are needed when loading a package into this function (don't call `library.dynam()` directly, as this will not work if the package is not installed in a ``standard'' location). `.First.lib` is invoked after `search()` has been updated, so `pos.to.env(match("package:name"), search())` will return the environment in which the package is stored. If calling `.First.lib` gives an error the loading of the package is abandoned, and the package will be unavailable. Similarly, if the option `".First.lib"` has a list element with the package's name, this element is called in the same manner as `.First.lib` when the package is loaded. This mechanism allows the user to set package ``load hooks'' in addition to startup code as provided by the package maintainers.

`.Last.lib` is called when a package is detached. Beware that it might be called if `.First.lib` has failed, so it should be written defensively. (It is called within `try`, so errors will not stop the package being detached.)

`.packages()` returns the ``base names'' of the currently attached packages invisibly whereas `.packages(all.available = TRUE)` gives (visibly) all packages available in the library location path `lib.loc`.

`.path.package` returns the paths from which the named packages were loaded, or if none were named, for all currently loaded packages. It will warn if the packages named are not loaded.

`.Autoloaded` contains the ``base names'' of the packages for which autoloading has been promised.

`.Library` is a character string giving the location of the default library, the ``library'' subdirectory of `R_HOME`. `.lib.loc` is a character vector with the locations of all library trees that R should use. It is initialized at startup from the environment variable `R_LIBS` (`RLIBS` as used by older versions of R is no longer accepted) (which should be a colon-separated list of directories at which R library trees are rooted) followed by `.Library`.

### Value

`library` returns the list of loaded (or available) packages (or `TRUE` if `logical.return` is `TRUE`). `require` returns a logical indicating whether the required package is available.

### Author(s)

R core; Guido Masarotto for the `all.available=TRUE` part of `.packages`.

### See Also

`attach`, `detach`, `search`, `objects`, `autoload`, `library.dynam`, `data`, `install.packages`. `INSTALL`, `REMOVE`

### Examples

    (.packages())               # maybe just "base"
    .packages(all = TRUE)       # return all available as char.vector
    library()                   # list all available packages
    library(lib = .Library)     # list all packages in the default library
    library(help = eda)         # documentation on package "eda"
    library(eda)                # load package "eda"
    require(eda)                # the same
    (.packages())               # "eda", too
    .path.package()
    .Autoloaded     # maybe "ctest"

    .lib.loc
    .Library == .lib.loc[length(.lib.loc)]  # `by definition'

    require(nonexistent)        # FALSE
    ## Suppose a package needs to call a shared library named "foo.EXT",
    ## where "EXT" is the system-specific extension.  Then you should use
    .First.lib <- function(lib, pkg) {
      library.dynam("foo", pkg, lib)
    }

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