Perl basice tutorial ebook

What is Perl? Optimized for String Manipulation and File I/O  Full support for Regular Expressions... String Operation Arithmeticle less than or equal to = cmp compare, return 1, 0, -1

Perl Basics

A Perl Tutorial

NLP Course - 2006

What is Perl?

 Optimized for String Manipulation and File I/O

 Full support for Regular Expressions

Running Perl Scripts

 Download ActivePerl from ActiveState

 Just run the script from a 'Command Prompt'

Basic Syntax

 Only single line comments

Scalars and Identifiers

 A variable name

 Case sensitive

 A single value (string or numerical)

 Accessed by prefixing an identifier with '$'

 Assignment with '='

$scalar = expression

 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

String Operation Arithmetic

le less than or equal to <=

ge greater than or equal to >=

cmp compare, return 1, 0, -1 <=>

Comparison Operators

Operator Operation

||, or logical or

&&, and logical and

!, not logical not

xor logical xor

Logical Operators

$newstring = $string1 $string2; #"potatohead"

$newerstring = $string1 x 2; #"potatopotato"

$string1 = $string2; #"potatohead"

String Operators

Check concat_input.pl

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

 Ordered collection of scalars

 Zero indexed (first item in position '0')

 Elements addressed by their positions

 @: reference to the array (or a portion of it, with [])

 $: reference to an element (used with [])

Associative Arrays - Hashes

 Arrays indexed on arbitrary string values

 Key-Value pairs

 Use the "Key" to find the element that has the

"Value"

 % : refers to the hash

 {}: denotes the key

 $ : the value of the element indexed by the key

(used with {})

Arrays Example

#!/usr/bin/perl

# Simple List operations

# Address an element in the list

# Join elements at positions 0, 1, 2 and 4 into a

white-space delimited string

print("orchestral brass: ",

join(" ",@brass[0,1,2,4]),

"\n");

@unsorted_num = ('3','5','2','1','4');

@sorted_num = sort( @unsorted_num );

# Sort the list

@numbers_10, "\n");

# Remove the last print("Numbers (1-9): ", pop(@numbers_10), "\n");

# Remove the first print("Numbers (2-9): ", shift(@numbers_10), "\n");

# Combine two ops print("Count elements (2-9): ",

$#@numbers_10;

# scalar( @numbers_10 ), "\n");

print("What's left (numbers 2-9): ",

@numbers_10, "\n");

Hashes Example

#!/usr/bin/perl

# Simple List operations

$player{"clarinet"} = "Susan Bartlett";

$player{"basson"} = "Andrew Vandesteeg";

$player{"flute"} = "Heidi Lawson";

$player{"oboe"} = "Jeanine Hassel";

Pattern Matching

searched for in a character string

 /pattern/

 =~: tests whether a pattern is matched

 !~: tests whether patterns is not matched

Pattern Matches Pattern Matches /def/ "define" /d.f/ dif

/\bdef\b/ a def word /d.+f/ dabcf

/^def/ def in start of

line

/d.*f/ df, daffff

/^def$/ def line /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

Character Ranges

Escape

Sequence Pattern Description

\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

Pattern Matching Options

Escape Sequence

Predefined Read-only Variables

EXAMPLE

$_ = "this is a sample string";

/sa.*le/; # matches "sample" within the string

The split and join Functions

The split function takes a regular expression and a string, and looks for all occurrences of the regular expression within that string The parts of the string that don't match the regular expression are returned in sequence as a list of values.

The join function takes a list of values and glues them together with a glue string between each list element.

String - Pattern Examples

String – Pattern Example