Ascertain File Accessibility

Description

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

Usage

file.access(names, mode = 0)

Arguments

Details

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.

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

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, and in recent Windows versions the underlying function in msvcrt.dll sometimes returns inaccurate values. It is better to wrap file open attempts in try instead.

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, try

Examples

fa <- file.access(dir("."))
table(fa) # count successes & failures