R: Read Text Lines from a Connection

readLines {base} | R Documentation

## Read Text Lines from a Connection

### Description

Read some or all text lines from a connection.

### Usage

    readLines(con = stdin(), n = -1L, ok = TRUE, warn = TRUE,
              encoding = "unknown", skipNul = FALSE)

### Arguments

`con` | a connection object or a character string.
`n` | integer. The (maximal) number of lines to read. Negative values indicate that one should read up to the end of input on the connection.
`ok` | logical. Is it OK to reach the end of the connection before `n > 0` lines are read? If not, an error will be generated.
`warn` | logical. Warn if a text file is missing a final EOL or if there are embedded nuls in the file.
`encoding` | encoding to be assumed for input strings. It is used to mark character strings as known to be in Latin-1 or UTF-8: it is not used to re-encode the input. To do the latter, specify the encoding as part of the connection `con` or via `options(encoding=)`: see the examples.
`skipNul` | logical: should nuls be skipped?

### Details

If the `con` is a character string, the function calls `file` to obtain a file connection which is opened for the duration of the function call. This can be a compressed file.

If the connection is open it is read from its current position. If it is not open, it is opened in `"rt"` mode for the duration of the call and then closed again.

If the final line is incomplete (no final EOL marker) the behaviour depends on whether the connection is blocking or not. For a non-blocking text-mode connection the incomplete line is pushed back, silently. For all other connections the line will be accepted, with a warning.

Whatever mode the connection is opened in, any of LF, CRLF or CR will be accepted as the EOL marker for a line.

Embedded nuls in the input stream will terminate the line currently being read, with a warning (unless `skipNul = TRUE` or `warn = FALSE)`).

If `con` is a not-already-open connection with a non-default `encoding` argument, the text is converted to UTF-8 and declared as such (and the `encoding` argument to `readLines` is ignored). See the examples.

### Value

A character vector of length the number of lines read.

The elements of the result have a declared encoding if `encoding` is `"latin1"` or `"UTF-8"`,

### Note

The default connection, `stdin`, may be different from `con = "stdin"`: see `file`.

### See Also

`connections`, `writeLines`, `readBin`, `scan`

### Examples

    cat("TITLE extra line", "2 3 5 7", "", "11 13 17", file = "ex.data",
        sep = "\n")
    readLines("ex.data", n = -1)
    unlink("ex.data") # tidy up

    ## difference in blocking
    cat("123\nabc", file = "test1")
    readLines("test1") # line with a warning

    con <- file("test1", "r", blocking = FALSE)
    readLines(con) # empty
    cat(" def\n", file = "test1", append = TRUE)
    readLines(con) # gets both
    close(con)

    unlink("test1") # tidy up

    ## Not run:
    # read a 'Windows Unicode' file
    A <- readLines(con <- file("Unicode.txt", encoding = "UCS-2LE"))
    close(con)
    unique(Encoding(A)) # will most likely be UTF-8

    ## End(Not run)

[Package base version 3.1.2 Index]