file.access {base}R Documentation

Ascertain File Accessibility

Description

Utility function to access information about files on the user's file systems.

Usage

file.access(names, mode = 0)

Arguments

names character vector containing file names.
mode integer specifying access mode required.

Details

Tilde-expansion is done on names: see path.expand.

The mode value can be the exclusive or of the following values

0
test for existence.
1
test for execute permission.
2
test for write permission.
4
test for read permission.

This function does uses the C function _access in ‘msvcrt.dll’, but was written using Win32 API functions.

Windows does not have the concept of an ‘executable file’, so this function regards directories and files with extension ‘.exe’, ‘.bat’, ‘.cmd’ and ‘.com’ as executable. (system makes the same assumption.)

Please note that it is not good to use this function to test before trying to open a file. On a multi-tasking system, it is possible that the accessibility of a file will change between the time you call file.access() and the time you try to open the file. It is better to wrap file open attempts in try.

Value

An integer vector with values 0 for success and -1 for failure.

Note

This is intended as a replacement for the S-PLUS function access, a wrapper for the C function of the same name, which explains the return value encoding. Note that the return value is false for success.

See Also

file.info for more details on permissions, Sys.chmod to change permissions, and try for a ‘test it and see’ approach.

file_test for shell-style file tests.

Examples

fa <- file.access(dir("."))
table(fa) # count successes & failures
d <- dir(file.path(R.home(), "bin"))
df <- dir(file.path(R.home(), "bin"), full.names = TRUE)
d[file.access(df, 0) == 0] # all exist
d[file.access(df, 1) == 0] # some are executable, some are not
d[file.access(df, 2) == 0] # hopefully all are readable
d[file.access(df, 4) == 0] # they may or may not be writable

[Package base version 2.9.1 Index]