1. Perl Basics A Perl Tutorial NLP Course - 2003

2. What is Perl?  Practical Extraction and Report Language  Interpreted Language Optimized for String Manipulation and File I/O Full support for Regular Expressions

3. Running Perl Scripts  Windows Download ActivePerl from ActiveState Just run the script from a 'Command Prompt' window  UNIX – Cygwin Put the following in the first line of your script #!/usr/local/bin/perl Make the script executable % chmod +x script_name Run the script %./script_name

4. Basic Syntax  Statements end with semicolon  Comments start with ‘#’ Only single line comments  Variables You don’t have to declare a variable before you access it You don't have to declare a variable's type

5. Scalars and Identifiers  Identifiers A variable name Case sensitive  Scalar A single value (string or numerical) Accessed by prefixing an identifier with '$' Assignment with '=' $scalar = expression

6. Strings  Quoting Strings With ' (apostrophe)  Everything is interpreted literally With " (double quotes)  Variables get expanded With ` (backtick)  The text is executed as a separate process, and the output of the command is returned as the value of the string Check 01_printDate.pl

7. StringOperationArithmetic lt less than < gt greater than > eq equal to == le less than or equal to <= ge greater than or equal to >= ne not equal to != cmp compare, return 1, 0, -1 Comparison Operators

8. OperatorOperation ||, or logical or &&, and logical and !, not logical not xor logical xor Logical Operators

9. OperatorOperation. string concatenation x string repetition.= concatenation and assignment $string1 = "potato"; $string2 = "head"; $newstring = $string1. $string2; #"potatohead" $newerstring = $string1 x 2; #"potatopotato" $string1.= $string2; #"potatohead" String Operators Check concat_input.pl

10. Perl Functions  Perl functions are identified by their unique names ( print, chop, close, etc)  Function arguments are supplied as a comma separated list in parenthesis. The commas are necessary The parentheses are often not Be careful! You can write some nasty and unreadable code this way! Check 02_unreadable.pl

11. Lists  Ordered collection of scalars Zero indexed (first item in position '0') Elements addressed by their positions  List Operators () : list constructor, : element separator [] : take slices (single or multiple element chunks)

12. List Operations  sort(LIST) a new list, the sorted version of LIST  reverse(LIST) a new list, the reverse of LIST  join(EXPR, LIST) a string version of LIST, delimited by EXPR  split(PATTERN, EXPR) create a list from each of the portions of EXPR that match PATTERN Check 03_listOps.pl

13. Arrays  A named list Dynamically allocated, can be saved Zero-indexed Shares list operations, and adds to them  Array Operators @ : reference to the array (or a portion of it, with []) $ : reference to an element (used with [])

14. Array Operations  push(@ARRAY, LIST) add the LIST to the end of the @ARRAY  pop(@ARRAY) remove and return the last element of @ARRAY  unshift(@ARRAY, LIST) add the LIST to the front of @ARRAY  shift(@ARRAY) remove and return the first element of @ARRAY  scalar(@ARRAY) return the number of elements in the @ARRAY Check 04_arrayOps.pl

15. Associative Arrays - Hashes  Arrays indexed on arbitrary string values Key-Value pairs Use the "Key" to find the element that has the "Value"  Hash Operators % : refers to the hash {}: denotes the key $ : the value of the element indexed by the key (used with {})

16. Hash Operations  keys(%ARRAY) return a list of all the keys in the %ARRAY  values(%ARRAY) return a list of all the values in the %ARRAY  each(%ARRAY) iterates through the key-value pairs of the %ARRAY  delete($ARRAY{KEY}) removes the key-value pair associated with {KEY} from the ARRAY

17. Pattern Matching  A pattern is a sequence of characters to be searched for in a character string /pattern/  Match operators =~: tests whether a pattern is matched !~: tests whether patterns is not matched

18. PatternMatchesPatternMatches /def/ "define" /d.f/ dif /\bdef\b/ a def word /d.+f/ dabcf /^def/ def word /d.*f/ df, daffff /^def$/ def /de{1,3}f/ deef, deeef /de?f/ df, def /de{3}f/ deeef /d[eE]f/ def, dEf /de{3,}f/ deeeeef /d[^eE]f/ daf, dzf /de{0,3}f/ up to deeef Patterns

19. Character Ranges Escape Sequence PatternDescription \d[0-9] Any digit \D[^0-9] Anything but a digit \w[_0-9A-Za-z] Any word character \W[^_0-9A-Za-z] Anything but a word char \s[ \r\t\n\f] White-space \S[^\r\t\n\f] Anything but white-space

20. Backreferences  Memory of matched portion of input /[a-z]+(.)[a-z]+\1[a-z]+/ asd-eeed-sdsa, sd-sss-ws NOT as.eee-dfg  They can even be accessed immediately after the pattern is matched (.) in the previous pattern is $1

21. Pattern Matching Options Escape Sequence Description g Match all possible patterns i Ignore case m Treat string as multiple lines o Only evaluate once s Treat string as single line x Ignore white-space in pattern

22. Substitutions  Substitution operator s/pattern/substitution/options  If $string = "abc123def"; $string =~ s/123/456/ Result: "abc456def" $string =~ s/123// Result: "abcdef" $string =~ s/(\d+)/[$1]/ Result: "abc[123]def"