source                 package:base                 R Documentation

Read R Code from a File or a Connection

Description:

     'source' causes R to accept its input from the named file or URL
     (the name must be quoted) or connection.  Input is read and
     'parse'd by from that file until the end of the file is reached,
     then the parsed expressions are evaluated sequentially in the
     chosen environment.

Usage:

     source(file, local = FALSE, echo = verbose, print.eval = echo,
            verbose = getOption("verbose"),
            prompt.echo = getOption("prompt"),
            max.deparse.length = 150, chdir = FALSE,
            encoding = getOption("encoding"),
            continue.echo = getOption("continue"),
            skip.echo = 0, keep.source = getOption("keep.source"))

Arguments:

    file: a connection or a character string giving the pathname of the
          file or URL to read from.  '""' indicates the connection
          'stdin()'.

   local: if 'local' is 'FALSE', the statements scanned are evaluated
          in the user's workspace (the global environment), otherwise
          in the environment calling 'source'.

    echo: logical; if 'TRUE', each expression is printed after parsing,
          before evaluation.

print.eval: logical; if 'TRUE', the result of 'eval(i)' is printed for
          each expression 'i'; defaults to the value of 'echo'.

 verbose: if 'TRUE', more diagnostics (than just 'echo = TRUE') are
          printed during parsing and evaluation of input, including
          extra info for *each* expression.

prompt.echo: character; gives the prompt to be used if 'echo = TRUE'.

max.deparse.length: integer; is used only if 'echo' is 'TRUE' and gives
          the maximal number of characters output for the deparse of a
          single expression.

   chdir: logical; if 'TRUE' and 'file' is a pathname, the R working
          directory is temporarily changed to the directory containing
          'file' for evaluating.

encoding: character vector.  The encoding(s) to be assumed when 'file'
          is a character string: see 'file'.  A possible value is
          '"unknown"' when the encoding is guesses: see the 'Details'.

continue.echo: character; gives the prompt to use on continuation lines
          if 'echo = TRUE'.

skip.echo: integer; how many comment lines at the start of the file to
          skip if 'echo = TRUE'.

keep.source: logical: should the source formatting be retained when
          echo expressions, if possible?

Details:

     Note that running code via 'source' differs in a few respects from
     entering it at the R command line.  Since expressions are not
     executed at the top level, auto-printing is not done.  So you will
     need to include explicit 'print' calls for things you want to be
     printed (and remember that this includes plotting by 'lattice',
     FAQ Q7.22).  Since the complete file is parsed before any of it is
     run, syntax errors result in none of the code being run. If an
     error occurs in running a syntactically correct script, anything
     assigned into the workspace by code that has been run will be kept
     (just as from the command line), but diagnostic information such
     as 'traceback()' will contain additional calls to 'eval.with.vis',
     an undocumented internal function.

     All versions of R accept input from a connection with end of line
     marked by LF (as used on Unix), CRLF (as used on DOS/Windows) or
     CR (as used on classic MacOS).  The final line can be incomplete,
     that is missing the final end-of-line marker.

     If 'options'("keep.source") is true (the default in interactive
     use), the source of functions is kept so they can be listed
     exactly as input. This imposes a limit of 128K bytes on the
     function size and a nesting limit of 265.  Use 'keep.source =
     FALSE' when these limits might take effect: if exceeded they
     generate an error.

     This paragraph applies if 'file' is a filename (rather than a
     connection).  If 'encoding = "unknown"', an attempt is made to
     guess the encoding.  The result of 'localeToCharset()' is used as
     a guide.  If 'encoding' has two or more elements, they are tried
     in turn until the file/URL can be read without error in the trial
     encoding.

     If 'file' is a connection (including one specified by '""', it is
     not possible to re-encode the input inside 'source', and so the
     'encoding' argument is just used to mark character strings in the
     parsed input: see 'parse'.

     Unlike input from a console, lines in the file or on a connection
     can contain an unlimited number of characters.

     When 'skip.echo > 0', that many comment lines at the start of the
     file will not be echoed.  This does not affect the execution of
     the code at all.  If there are executable lines within the first
     'skip.echo' lines, echoing will start with the first of them.

     If 'echo' is true and a deparsed expression exceeds
     'max.deparse.length', that many characters are output followed by
     ' .... [TRUNCATED] '.

References:

     Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) _The New S
     Language_. Wadsworth & Brooks/Cole.

See Also:

     'demo' which uses 'source'; 'eval', 'parse' and 'scan';
     'options("keep.source")'.

     'sys.source' which is a streamlined version to source a file into
     an environment.

Examples:

     ## If you want to source() a bunch of files, something like
     ## the following may be useful:
      sourceDir <- function(path, trace = TRUE, ...) {
         for (nm in list.files(path, pattern = "\\.[RrSsQq]$")) {
            if(trace) cat(nm,":")           
            source(file.path(path, nm), ...)
            if(trace) cat("\n")
         }
      }

