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Checking Your Access to a File
CodeExpectedActual
File.readable?('/bin/ls')
 true true 
File.readable?('/etc/passwd-')
 false false 
filename = 'test_file'
File.open(filename, 'w') {}
File.writable?(filename)
 true true 
File.writable?('/bin/ls')
 false false 
File.executable?('/bin/ls')
 true true 
File.executable?(filename)
 false false 
File.owned? 'test_file'
 true true 
File.grpowned? 'test_file'
 true true 
File.owned? '/bin/ls'
 false false 
File.lstat('test_file').mode & 0777       # Keep only the permission bits.
 420 420 
def what_can_i_do?
  sys = Process::Sys	
  puts "UID=#{sys.getuid}, GID=#{sys.getgid}"
  puts "Effective UID=#{sys.geteuid}, Effective GID=#{sys.getegid}"
  file = '/bin/ls'
  can_do = [:readable?, :writable?, :executable?].inject([]) do |arr, method|
    arr << method if File.send(method, file); arr
  end
  puts "To you, #{file} is: #{can_do.join(', ')}"
end
what_can_i_do?
 
UID=0, GID=0
Effective UID=0, Effective GID=0
To you, /bin/ls is: readable?, writable?, executable?
 
UID=1000, GID=1000
Effective UID=1000, Effective GID=1000
To you, /bin/ls is: readable?, executable?
 
Process.uid = 1000
what_can_i_do?
 
UID=0, GID=0
Effective UID=1000, Effective GID=0
To you, /bin/ls is: readable?, executable?
 
UID=1000, GID=1000
Effective UID=1000, Effective GID=1000
To you, /bin/ls is: readable?, executable?