R: Read Text Lines from a Connection

readLines {base} | R Documentation

## Read Text Lines from a Connection

### Description

Read text lines from a connection.

### Usage

    readLines(con = stdin(), n = -1, ok = TRUE)

### 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 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.

### Details

If the `con` is a character string, the functions call `file` to obtain an file connection which is opened for the duration of the function call.

If the connection is open it is read from its current position. If it is not open, it is opened 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 blocking text-mode connection (or a non-text-mode connection) the line will be accepted, with a warning. For a non-blocking text-mode connection the incomplete line is pushed back, silently.

### Value

A character vector of length the number of lines read.

### See Also

`connections`, `writeLines`, `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

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