R: Read R Code from a File or a Connection

source {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")
        }
     }

[Package base version 2.8.1 Index]