file.access: 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’.

Value

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

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.

unix Permission will be computed for real user ID and real group ID (rather than the effective IDs). windows 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 and Sys.which make the same assumption.)

UTF-8-encoded file names not valid in the current locale can be used.

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.

Examples

Run this code

fa <- file.access(dir("."))
table(fa) # count successes & failures
 windows
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, 4) == 0] # hopefully all are readable
d[file.access(df, 2) == 0] # they may or may not be writable

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