CIT 383: Administrative Scripting Files CIT 383: Administrative Scripting

CIT 383: Administrative Scripting Topics Creating File Objects Reading Files Writing Files 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 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