CIT 383: Administrative Scripting

1. CIT 383: Administrative Scripting Commands CIT 383: Administrative Scripting

2. Topics Commands • System • Exec • Command Quotes • Popen • Expect Time • UNIX Time • Time Zones • Calendars • Ruby DateTime classes

3. CIT 383: Administrative Scripting System Executes command string in a subshell system(“tar cjf ruby.tar.bz2 *.rb”) system(“cut –d: -f1 /etc/passwd | sort”) All shell features are available Globbing (*/*.c) Tilde expansion (~jsmith) I/O redirection Pipes

4. CIT 383: Administrative Scripting System with Multiple Arguments Multiple arguments have different behavior First argument is name of command. Later arguments are command line arguments. None are interpreted by shell. Examples system(“echo *”) prints all files in directory system(“echo”, “*”) prints a * system(“tar”, “c”, “f”, “ruby.tar”, “rubyfiles/”)

5. CIT 383: Administrative Scripting System Security Archiving user specified files files = gets system(“tar cf ruby.tar #{files}”) What if the user enters “*; rm –rf/”? tar cjf ruby.tar.bz2 * rm –rf / Use multiple argument form to avoid this bug. files = gets system(“tar”, “c”, “f”, “ruby.tar”, files)

6. CIT 383: Administrative Scripting Exec Replaces current process by running command. exec(“ls –l”) # program never reaches this point Single argument form invokes shell exec(“echo *”) Multiple argument form does not exec(“echo”, “*”)

7. CIT 383: Administrative Scripting Command Quotes Ruby will run commands in backquotes os = `uname` os = %x|uname| Return value is output of command as String. Command quotes invoke a subshell: files = `echo *` sortedfiles = `echo * | sort`

8. CIT 383: Administrative Scripting Popen Pipe Open IO.popen(command_string, mode) Opens command like a file r: read from command’s STDOUT. w: write to command’s STDIN. Similar to command quotes in read mode: uname_fh = IO.popen(‘uname –a’, ‘r’) unixname = uname_fh.readlines

9. CIT 383: Administrative Scripting Popen Popen offers more control than command quotes. Use less memory (read a line at a time.) Obtain partial output immediately. Examples vmfh = popen(“vmstat 5 5”) # Throw away header lines then print vmfh.gets vmfh.gets vmfh.each do |vmline| puts vmline end

10. CIT 383: Administrative Scripting Expect Automation tool for interactive processes. fsck ftp minicom passwd telnet Methods spawn: start an external command expect: wait for command to output pattern send: send string to command as input

11. CIT 383: Administrative Scripting Expect PTY.spawn(‘telnet zork.nku.edu’) do |r_f,w_f,pid| r_f.expect(/^Username.*: /) do w_f.print ‘jsmith’ end r_f.expect('Password:') do w_f.print password end r_f.expect(‘$ ‘) do w_f.print “passwd #{password} spameggs“ end end

12. CIT 383: Administrative Scripting UNIX Time UNIX time is seconds since the midnight, Jan 1, 1970. Most OS represent time as 32-bit signed int. Lowest time: 1901-12-13 Highest time: 2038-01-18 OS need to upgrade to 64 bits to avoid Y2038 problem.

13. CIT 383: Administrative Scripting Time Zones

14. CIT 383: Administrative Scripting UTC: Coordinated Universal Time Local time at royal observatory at Greenwich • GMT established at 1884 conference. • Prime meridian (0 degrees longitude.) International Atomic Time (TAI) • Based on atomic clock, established in 1958. • Includes leap seconds to account for lengthening of day as the Earth’s rotation slows. Time zones defined by offset from UTC.

15. CIT 383: Administrative Scripting Calendars Julian Calendar • Introduced by Julius Caesar in 46BC. • Reform of older Roman calendar system, which had leap months. • 365 days, 12 months, leap day every 4 years. • Month Quintilius became July. Gregorian Calendar • Proposed by Aloysius Lilius. • Decreed by Pope Gregory XIII in 1582 (adopted by English 1752) • Dropped 10 days from Julian calendar. • Changed leap day rules • Leap day every 4 years except • if year is divisible by 100 except • years divisible by 400 are still leap years.

16. CIT 383: Administrative Scripting Ruby DateTime classes Date Mutable date objects. Time Mutable time objects that also include date. DateTime Immutable objects with date and time.

17. CIT 383: Administrative Scripting Creating a Date object Date.today • Create Date object for current day. Date.new(year, month, day) • Create Date object based on year, month, and day. Date.parse(string) • Create Date object from date stored in string.

18. CIT 383: Administrative Scripting Creating a Time object Time.gm(year <,month,day,hour,min,sec>) • Create time based on specified values. • Interpreted as GMT (UTC). Time.local(year <,month,day,hour,min,sec>) • Create time based on specified values. • Interpreted as local set time zone. Time.new • Create Time object initialized to current time. Time.now • Same as Time.new.

19. CIT 383: Administrative Scripting Creating a DateTime object DateTime.new • Create Time object initialized to current time. DateTime.now • Same as Time.new. DateTime.parse(string) • Create DateTime from date stored in string

20. CIT 383: Administrative Scripting Date and Time Arithmetic Addition and substraction of constants • Increment by day (Date) or second (Time) • Decrement by day (Date) or second (Time) Subtraction of dates • Determine days between two Dates. • Determine seconds between two Times.

21. CIT 383: Administrative Scripting Ranges Sequence of values 1..10 ?a..?z Methods min max include?(num) Ranges as Intervals (1..10) === 4 # true (1..10) === 99 # false (1..10) === 2.718 # true

22. CIT 383: Administrative Scripting Ranges and Arrays Ranges provide iterator methods • Including the each method. Ranges can be converted to Arrays • Use the to_a method. Ranges are stored efficiently • Only initial and final values are stored. • Do not convert 1..2**32 to an Array.

23. CIT 383: Administrative Scripting Date Ranges today = Date.today nextweek = today + 7 weekdates = today..nextweek weekdates.each do |date| puts date end

24. CIT 383: Administrative Scripting Waiting sleep(num) • Waits for num seconds. • Does not use any CPU during sleep. Applications • Wait before retrying an action that failed. • Periodic processes (check file every minute.)

25. 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. • Dave Thomas with Chad Fowler and Andy Hunt, Programming Ruby, 2nd edition, Pragmatic Programmers, 2005.