1. CIT 383: Administrative Scripting
Files
CIT 383: Administrative Scripting

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

3. 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

4. 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

5. 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

6. 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

7. 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

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

9. 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

10. 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

11. 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

12. 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

13. CIT 383: Administrative Scripting
References
Michael Fitzgerald, Learning Ruby, O’Reilly,
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,
Dave Thomas with Chad Fowler and Andy Hunt, Programming Ruby, 2nd edition, Pragmatic Programmers, 2005.
CIT 383: Administrative Scripting