POSIX

system: Run a program like os.system, but without a shell
file: filename of program to run
...: arguments to the program
returns
status: exit code, or nil if fork or wait fails
[reason]: error message, or exit type if wait succeeds

euidaccess: Check permissions like access, but for euid
Based on the glibc function of the same name. Does not always check
for read-only file system, text busy, etc., and does not work with
ACLs &c.
file: file to check
mode: checks to perform (as for access)
returns
ret: 0 if access allowed; -1 otherwise (and errno is set)