CIT 383: Administrative Scripting Files and Directories CIT 383: Administrative Scripting

CIT 383: Administrative Scripting Topics Creating File Objects Reading Files Writing Files Directories Inodes File Management Command Line Arguments CIT 383: Administrative Scripting

CIT 383: Administrative Scripting Files File class constructor arguments Pathname Access type a: append a+: read-write (starts at end of file if file exists) r: read r+: read-write w: write (truncate file to zero length) w+: read-write (truncate file to zero length) Examples pwfile = File.new(‘/etc/passwd’, ‘r’) usrfile = File.new(‘userlist’, ‘w’) logfile = File.new(‘/var/log/mylog’, ‘a’) CIT 383: Administrative Scripting

CIT 383: Administrative Scripting Reading Files getc: reads a single character at current pos gets: reads a single line at current pos seek: changes position in file tell: returns position in file read: reads entire file as a string readlines: reads file as an array of lines CIT 383: Administrative Scripting

Reading a file line by line File class each_line iterator fh.each_line do |line| # do stuff with line here end While loop while line = fh.gets CIT 383: Administrative Scripting

CIT 383: Administrative Scripting Writing Files putc: writes a single character at current pos print: writes a single line at current pos puts: writes line at current pos with newline seek: changes position in file tell: returns position in file write: writes to file, returns bytes written CIT 383: Administrative Scripting

CIT 383: Administrative Scripting Line Endings Getting rid of line end characters line_without_ending = line.chomp OR line.chomp! Outputting line ending characters puts inserts a line ending print does not add a line ending CIT 383: Administrative Scripting

CIT 383: Administrative Scripting Global File Objects $stdin Default object for getc and gets $stdout Default object for puts $stderr CIT 383: Administrative Scripting

CIT 383: Administrative Scripting Closing Files After reading/writing to a file, close it. file.close What if an error kills program before close? Use open instead of new to auto close File.open(pathname,’r’) do |fh| fh.gets end CIT 383: Administrative Scripting

CIT 383: Administrative Scripting Data Munging Data munging: to convert data from one format to another format, possibly sorting, summarizing, or otherwise modifying it in the process. CIT 383: Administrative Scripting

CIT 383: Administrative Scripting Skipping lines Skipping blank lines file.each_line do |line| next if line == "\n" puts line end Skipping lines beginning with a character next if line[0] == ?# CIT 383: Administrative Scripting

CIT 383: Administrative Scripting Delimited Data pwfields = [:username, :password, :uid, :gid, :gcos, :homedir, :shell] pwline = ‘root:x:0:0:root:/root:/bin/sh’ pwitems = pwline.split(‘:’) pwhash = Hash.new i = 0 while i < pwitems.size pwhash[pwfields[i]] = pwitems[i] i = i + 1 end CIT 383: Administrative Scripting

CIT 383: Administrative Scripting Directories Directory: table of name to inode mappings $ ls –i / 2272929 bin 65409 boot 49057 cdrom 2260 dev 850305 etc 2 home 2371041 initrd 49075 initrd.img 49058 initrd.img.old 948417 lib CIT 383: Administrative Scripting

Accessing Directories thisdir = Dir.new(pathname) absolutedir = Dir.new(‘/home/smi/dir1’) relativedir = Dir.new(‘smi/dir1’) currentdir = Dir.new(‘.’) uponedir = Dir.new(‘..’) Methods entries: returns array of filenames each: iterates over each file in directory CIT 383: Administrative Scripting

CIT 383: Administrative Scripting Inodes An inode is a disk structure that contains Size of the file in bytes. Device ID that identifies device where file is located. UID of the file’s owner. GID of the file’s group. File mode (permissions.) Timestamps ctime: inode change time mtime: time file content was last modified atime: time file content was last accessed Reference count that identifies how many directory entries point to inode. Pointers to disk blocks containing file data. CIT 383: Administrative Scripting

Hard and Symbolic Links A hard link is A directory entry that points to an inode. Deleting a file with rm just removes the directory entry. File data is not removed until all links removed. A symbolic link is A file that contains a pathname. Deleting the link does not affect the file. Deleting a file with rm invalidates the symbolic link but does not remove it from filesystem. CIT 383: Administrative Scripting

Basic File Permissions Three sets of permissions: owner, group, world Each set represented by an octal digit. Each permission (r,w,x) one bit in octal digit. Special permissions: setuid, setgid, sticky. ex: chmod 0644 file u: rw, g: r, o: r ex: chmod 0711 bin u: rwx, g: x, o: x 4 read setuid 2 write setgid 1 execute sticky CIT 383: Administrative Scripting

CIT 383: Administrative Scripting File::Stat The File::Stat class allows access to inodes stat = File::Stat.new(pathname) OR file = File.new(pathname) stat = file.stat Methods size: size of file in bytes uid: UID of file owner gid: GID of file owner mode: file permissions in octal mtime,ctime,atime: file timestamps CIT 383: Administrative Scripting

Querying File Attributes directory? – Is file a directory? symlink? – Is file a symbolic link? file? – Is file an ordinary file (not a directory, device, or symlink)? readable? – Is file readable by me? writable? – Is file writable by me? executable? – Is file executable by me? setuid? – Is file setuid? setgid? – Is file setgid? sticky? – Is the sticky bit set? CIT 383: Administrative Scripting

CIT 383: Administrative Scripting File Management The FileUtils class provides methods that emulate the functionality of UNIX commands: chmod chown cp ln mkdir mv rm rmdir CIT 383: Administrative Scripting

Command Line Arguments Using command line arguments ./test.rb arg1 arg2 arg3 Accessing command line arguments Ruby provides them via the ARGV array: ARGV.each do |arg| puts arg end CIT 383: Administrative Scripting

CIT 383: Administrative Scripting References Michael Fitzgerald, Learning Ruby, O’Reilly, 2008. David Flanagan and Yukihiro Matsumoto, The Ruby Programming Language, O’Reilly, 2008. Hal Fulton, The Ruby Way, 2nd edition, Addison- Wesley, 2007. Robert C. Martin, Clean Code, Prentice Hall, 2008. Dave Thomas with Chad Fowler and Andy Hunt, Programming Ruby, 2nd edition, Pragmatic Programmers, 2005. CIT 383: Administrative Scripting