R: Read R Code from a File, a Connection or Expressions

source {base} | R Documentation

## Read R Code from a File, a Connection or Expressions

### Description

`source` causes R to accept its input from the named file or URL or connection or expressions directly. Input is read and `parse`d from that file until the end of the file is reached, then the parsed expressions are evaluated sequentially in the chosen environment.

`withAutoprint(exprs)` is a wrapper for `source(exprs = exprs, ..)` with different defaults. Its main purpose is to evaluate and auto-print expressions as if in a toplevel context, e.g, as in the R console.

### Usage

    source(file, local = FALSE, echo = verbose, print.eval = echo,
           exprs, spaced = use_file,
           verbose = getOption("verbose"),
           prompt.echo = getOption("prompt"),
           max.deparse.length = 150, width.cutoff = 60L,
           deparseCtrl = "showAttributes",
           chdir = FALSE,
           encoding = getOption("encoding"),
           continue.echo = getOption("continue"),
           skip.echo = 0, keep.source = getOption("keep.source"))

    withAutoprint(exprs, evaluated = FALSE, local = parent.frame(),
                  print. = TRUE, echo = TRUE, max.deparse.length = Inf,
                  width.cutoff = max(20, getOption("width")),
                  deparseCtrl = c("keepInteger", "showAttributes", "keepNA"),
                  ...)

### Arguments

`file` | a connection or a character string giving the pathname of the file or URL to read from. `""` indicates the connection `stdin()`.
`local` | `TRUE`, `FALSE` or an environment, determining where the parsed expressions are evaluated. `FALSE` (the default) corresponds to the user's workspace (the global environment) and `TRUE` to the environment from which `source` is called.
`echo` | logical; if `TRUE`, each expression is printed after parsing, before evaluation.
`print.eval, print.` | logical; if `TRUE`, the result of `eval(i)` is printed for each expression `i`; defaults to the value of `echo`.
`exprs` | for `source()` and `withAutoprint(*, evaluated=TRUE)`: instead of specifying `file`, an `expression`, `call`, or `list` of `call`'s, but not an unevaluated “expression”. for `withAutoprint()` (with default `evaluated=FALSE`): one or more unevaluated “expressions”.
`evaluated` | logical indicating that `exprs` is passed to `source(exprs= *)` and hence must be evaluated, i.e., a formal `expression`, `call` or `list` of calls.
`spaced` | logical indicating if newline (hence empty line) should be printed before each expression (when `echo = TRUE`).
`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.
`width.cutoff` | integer, passed to `deparse()` which is used (only) when there are no source references.
`deparseCtrl` | `character` vector, passed as `control` to `deparse()`, see also `.deparseOpts`. In R version <= 3.3.x, this was hardcoded to `"showAttributes"`, which is the default currently; `deparseCtrl = "all"` may be preferable, when strict back compatibility is not of importance.
`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 guessed: see the ‘Encodings’ section.
`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 echoing expressions, if possible?
`...` | (for `withAutoprint()`:) further (non-file related) arguments to be passed to `source(.)`.

### 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 `withVisible`.

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 Mac OS) and map this to newline. The final line can be incomplete, that is missing the final end-of-line marker.

If `keep.source` is true (the default in interactive use), the source of functions is kept so they can be listed exactly as input.

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]` .

### Encodings

By default the input is read and parsed in the current encoding of the R session. This is usually what it required, but occasionally re-encoding is needed, e.g. if a file from a UTF-8-using system is to be read on Windows (or vice versa).

The rest of this paragraph applies if `file` is an actual filename or URL (and not `""` nor 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 an actual `encoding` is specified (rather than the default or `"unknown"`) in a Latin-1 or UTF-8 locale then character strings in the result will be translated to the current encoding and marked as such (see `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 in Latin-1 and UTF-8 locales: see `parse`.

### 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.

‘The R Language Definition’ for a discussion of source directives.

### Examples

    someCond <- 7 > 6
    ## want an if-clause to behave "as top level" wrt auto-printing :
    ## (all should look "as if on top level", e.g. non-assignments should print:)
    if(someCond) withAutoprint({
       x <- 1:12
       x-1
       (y <- (x-5)^2)
       z <- y
       z - 10
    })

    ## 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")
        }
     }

    suppressWarnings( rm(x,y) ) # remove 'x' or 'y' from global env
    withAutoprint({ x <- 1:2; cat("x=",x,"\n"); y <- x^2 })
    ## x and y now exist:
    stopifnot(identical(x, 1:2), identical(y, x^2))

    withAutoprint({ formals(sourceDir); body(sourceDir) },
                  max.dep = 20, verbose = TRUE)

[Package base version 3.5.1 Index]