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. `.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, 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(), quiet = FALSE)
     .lib.loc
     .Library
     .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'.

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 a character vector of all
          available packages in `lib.loc'.

   quiet: logical.  Should `.path.package' not give warnings or an
          error if the package(s) are not loaded?

_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.

     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. Unless `quiet = TRUE' it will warn if some of the
     packages named are not loaded, and given an error if none are.

     `.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'.

_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'. `INSTALL', `REMOVE'

_E_x_a_m_p_l_e_s:

     (.packages())               # maybe just "base"
     .packages(all = TRUE)       # return all available as character 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)
     }

