file.access {base}

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. Tilde-expansion will be done: see path.expand.

mode

integer specifying access mode required: see ‘Details’.

Details

The mode value can be the exclusive or (xor), i.e., a partial sum of the following values, and hence must be in 0:7,

0

test for existence.

1

test for execute permission.

2

test for write permission.

4

test for read permission.

Permission will be computed for real user ID and real group ID (rather than the effective IDs).

Please note that it is not a good idea 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 was written 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