Question

I am trying to learn ruby(1.8.7). I have programmed in php for some time and I consider myself proficient in that language. I have a book which I reference, and I have looked at many introductory ruby tutorials, but I cannot figure this out.

myFiles = ['/Users/', '/bin/bash', 'Phantom.file']
myFiles.each do |cFile|
  puts "File Name: #{cFile}"
  if File.exists?(cFile)
    puts "#{cFile} is a file"
    cFileStats = File.stat(cFile)
    puts cFileStats.inspect
    cFileMode = cFileStats.mode.to_s()
    puts "cFileMode Class: " + cFileMode.class.to_s()
    puts "length of string: " + cFileMode.length.to_s()
    printf("Mode: %o\n",  cFileMode)
    puts "User: " + cFileMode[3,1]
    puts "Group: " + cFileMode[4,1]
    puts "World: " + cFileMode[5,1]
  else
    puts "Could not find file: #{cFile}"    
  end
  puts
  puts
end

produces the following output:

File Name: /Users/
/Users/ is a file
#<File::Stat dev=0xe000004, ino=48876, mode=040755, nlink=6, uid=0, gid=80, rdev=0x0, size=204, blksize=4096, blocks=0, atime=Sun Sep 04 12:20:09 -0400 2011, mtime=Thu Sep 01 21:29:08 -0400 2011, ctime=Thu Sep 01 21:29:08 -0400 2011>
cFileMode Class: String
length of string: 5
Mode: 40755
User: 7
Group: 7
World: 


File Name: /bin/bash
/bin/bash is a file
#<File::Stat dev=0xe000004, ino=8672, mode=0100555, nlink=1, uid=0, gid=0, rdev=0x0, size=1371648, blksize=4096, blocks=1272, atime=Sun Sep 04 16:24:09 -0400 2011, mtime=Mon Jul 11 14:05:45 -0400 2011, ctime=Mon Jul 11 14:05:45 -0400 2011>
cFileMode Class: String
length of string: 5
Mode: 100555
User: 3
Group: 3
World: 


File Name: Phantom.file
Could not find file: Phantom.file

Wh is the string length different than expected? (Should be 5 for users, 6 for /bin/bash)? Why are the substrings not puling the correct characters. I understand World not being populated when referencing a 5 character string, but the offsets seem off, and in the case of /bin/bash 3 does not even appear in the string.

Thanks

Scott

Answer 1

This is a nice one.

When a number is preceeded by a 0, it is represented as octal. What you are actually getting for bin/bash:

0100755 to decimal = 33261
"33261".length = 5

And for /Users:

040755 to decimal = 16877
"16877".length = 5

Add the following line:

puts cFileMode

And you will see the error.

to_s takes an argument which is the base. If you call to_s(8) then it should work.

cFileMode = cFileStats.mode.to_s(8)

EDIT

files = ['/home/', '/bin/bash', 'filetest.rb']
files.each do |file|
  puts "File Name: #{file}"
  if File.exists?(file)
    puts "#{file} is a file"
    file_stats = File.stat(file)
    puts file_stats.inspect
    file_mode = file_stats.mode.to_s(8)
    puts "cFileMode Class: #{file_mode.class}"
    p file_mode
    puts "length of string: #{file_mode.length}"
    printf("Mode: #{file_mode}")
    puts "User: #{file_mode[-3,1]}"
    puts "Group: #{file_mode[-2,1]}"
    puts "World: #{file_mode[-1,1]}"
  else
    puts "Could not find file: #{file}"    
  end
  puts
  puts
end