1. LING/C SC/PSYC 438/538 Lecture 5 Sandiway Fong

2. Today’s Topics File input/output – open, <> References Perl modules Homework 2: due next Monday by midnight – email: sandiway@email.arizona.edusandiway@email.arizona.edu – one PDF file – subject: 438/538 homework 2

3. File I/O Files: must be opened for reading “ ” (overwrite or append mode “>>”) Shell syntax: I/O redirection “ ” Opening a file creates a file handle (Perl variable) – not to be confused with filename Supply the file handle for read/write Step 1: call open()

4. File I/O Step 2: use the <> operator: $in is the file handle instantiated by the open() call

5. File I/O Line by line: open($txtfile, $ARGV[0]) or die "$ARGV[0] not found!\n"; while ($line = ) { print "$line"; } close($txtfile) the command $line = inside the condition reads in a line from the file referenced by the file handle $txtfile and places that line into the variable $line (including the newline at the end of the line) At the end of the file, $line is just an empty string (equivalent to false). the filename is the first parameter to the perl program (arguments go in @ARGV).

6. More complex data structures Arrays and hashes may only contain scalars Question: How to accomplish nesting, i.e. put non-scalars inside? Answer: use references (pointers), which happen to be scalars http://perldoc.perl.org/p erlreftut.html http://perldoc.perl.org/p erlreftut.html (actually a reference is just an unsigned number: computer address)

7. References Two ways to make a reference: Remember bracketing when initializing: ( ) List – can be used for both arrays and hashes [] Reference to an array {} Reference to a hash Remember bracketing when initializing: ( ) List – can be used for both arrays and hashes [] Reference to an array {} Reference to a hash

8. References Example: array of arrays Note: uses Make Rule 2 Let’s figure out what the following mean: de-reference

9. References Looping (using for/foreach) with array/hash references: Be careful! $aref->[3] and $aref[3] are different

10. References Code: $a = [1, 2, 3, 4, 5]; print $a+1 What happens here?

11. References Looping (using for/foreach) with array/hash references: Be careful! $href->{‘red’} vs. $href{‘red’} are different.

12. Experiment Unicode encoding (utf-8)

13. Experiment Note: open pragma most general solution

14. Perl Modules CPAN: Comprehensive Perl Archive Network sudo cpanm Unicode::CaseFold terminal command

15. cpanm Ubuntu: Ubuntu: sudo apt-get cpanminus

16. cpanm OSX: assume command line tools have been installed – xcode-select --install uses program curl (cURL) – a command line tool for getting or sending files using URL syntax bash-3.2$ which cpanm bash-3.curl -L http://cpanmin.us | perl - --sudo App::cpanminus % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 100 303 0 303 0 0 56 0 --:--:-- 0:00:05 --:--:-- 1553 100 262k 100 262k 0 0 22916 0 0:00:11 0:00:11 --:--:-- 64374 --> Working on App::cpanminus Fetching http://www.cpan.org/authors/id/M/MI/MIYAGAWA/App-cpanminus-1.7000.tar.gz... OK Configuring App-cpanminus-1.7000... OK Building and testing App-cpanminus-1.7000... Password: OK Successfully installed App-cpanminus-1.7000 1 distribution installed bash-3.2$ which cpanm /usr/local/bin/cpanm

17. Example of module use

18. Homework 2 Question 1 (10pts) Create a file data.txt (example): 1.Love for the the Bronx Bombers bubbled up in the absence of some local franchise. 2.On on on the table, we have some eggs. 3.I have home sharing turned on, on both my computer and my apple tv. Write a Perl program that detects repeated words (many spell check/grammar programs can do this) Your program should read in data.txt and print a message stating the line number, the repeated word and its position if one exists. Example output: – perl repeated.perl data.txt – Line 1: word 3, “the” repeated 2 times – Line 2: word 1, “on” repeated 3 times Submit your program and examples of its output Note: case

19. Homework 2 Useful functions: chomp vs. chop split a string into words Note: multiple spaces ok with “ “ version

20. Homework 2 Question 2: describe how a repeated word program could stop flagging legitimate examples of repeated words in a sentence – Examples: I wish that that question had an answer Because he had had too many beers already, he skipped the Friday office happy hour

21. Homework 2 Microsoft Word: