library                 package:base                 R Documentation

_L_o_a_d_i_n_g _a_n_d _L_i_s_t_i_n_g _o_f _P_a_c_k_a_g_e_s

_D_e_s_c_r_i_p_t_i_o_n:

     `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.

_U_s_a_g_e:

     library(package, help = NULL, lib.loc = .lib.loc,
             character.only = FALSE, logical.return = FALSE,
             warn.conflicts = TRUE)
     require(package, quietly = FALSE, warn.conflicts = TRUE)
     provide(package)

     .First.lib(libname, pkgname)

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

_A_r_g_u_m_e_n_t_s:

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'.

 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.

all.available: logical; if `TRUE' return `character' vector of all
          available packages in `lib.loc'.

_D_e_t_a_i_l_s:

     `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.  `require' also
     checks the list `.Provided'.

     `provide' allows code to register services that it provides.  The
     argument is stored in the list `.Provided'.  `provide' returns
     `FALSE' if the package was already present in `.Provided' or among
     the packages in `search()'.  The main use for `provide' is when
     multiple packages share code.  This is most likely when the code
     implements features present in S(-PLUS) but not in R.

     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 tree
     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.

     `.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 semicolon-separated
     list of directories at which R library trees are rooted) followed
     by `.Library'.

_V_a_l_u_e:

     `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.

_A_u_t_h_o_r(_s):

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

_S_e_e _A_l_s_o:

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

_E_x_a_m_p_l_e_s:

     .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
     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)
     }

