Perl

Perl There is more than one way to do it (TIMTOWDI)

Perl(Practical Extraction and Reporting Language)is a scripting language, designed by Larry Wall. Perl is a language optimized for scanning arbitrary text files, extracting information from those text files,and printing reports based on that information. (From version 5 Pearl uses both compiler and interpreter)

What is a scripting language? 

Operating systems can do many things − − −

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copy, move, create, delete, compare files execute programs, including compilers schedule activities, monitor processes, etc.

A command-line interface gives you access to these functions, but only one at a time A scripting language is a “wrapper” language that integrates OS functions

Major scripting languages   

UNIX has sh, Perl Macintosh has AppleScript, Frontier Windows has no major scripting languages −

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probably due to the weaknesses of DOS

Generic scripting languages include: − − −

Perl (most popular) Tcl (easiest for beginners) Python (new, Java-like, best for large programs)

Running Perl 

#!/usr/local/bin/perl (tells the file to run

through perl [ only on *nix platform] ) 

Use .pl extension

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Perl programName (to run the program)

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Perl -d programName (to run using debugger)

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Perl -w programName (enable many useful warnings (RECOMMENDED) )

“Hello, World Of Perl” #!/usr/local/bin/perl #Program to do the obvious print 'Hello world.'; #Print a message

Perl is a free form language  Perl statements end with semicolons  Perl is case-sensitive  Perl is compiled and run in a single operation  Comments are # to end of line 

−

But the first line, #!/usr/local/bin/perl, tells where to find the Perl compiler on your system

Input 

Most heavily used input operator is th angle operator. <STDIN> is used to read line from standard input.

e.g. chomp($name=<STDIN>); The <> operator may also be used as it implicitly uses STDIN.

Output The print and printf functions are built-in functions used to display output.  The print function arguments consist of a comma-separated list of strings and/or numbers.  The printf function is similar to the C printf() function and is used for formatting output.  print value, value, value; printf ( string format [, mixed args [, mixed ...]] ); eg. print "Hello, world\n"; printf("Meet %s:Age %d:Salary \$%10.2f\n",  "John", 40, 55000);

Literals All computer programs have to handle data. In every program there are certain kinds of data that do not change with time. They are called Literals. Mainly two types of literals exist in Perl. Numeric Literal

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String Literal

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Named Constants can also be define in perl e.g.use constant BUFFER_SIZE => 4096;

Numeric Literal In Perl numbers can be expressed in decimal , hexadecimal or octal notation.  Octal numbers are preceded by a 0 eg. 023 is equivalent to 1910 hexadecimal numbers are preceded by 0x eg. 0xfe is equivalent to 25410 

Underscore( _ ) can be used to make large numbers more readable. eg. 4_976_297_305 is same as 4976297305 

String Literal A string is a sequence of characters enclosed by either double quotes (") or single quotes (').They differ in variable substitution and in the way escape characters are handled. Example"Hell is filled with ameture musicians." 'Give me $500'

Quoting format Different quoting mechanisms can be used to make different kinds of values. Double quotes do 

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Variable interpolation (replacement of variable name by its value) Backslash interpretation (escape characters)

While single quotes(') don't do all these.

Escape characters Code

Meaning

\n Newline \r Carriage return \t Horizontal Tab \f form feed \b backspace \a Alert(bell) \e ESC character \033 ESC in octal \x7f DEL om hexadecimal \cC Control-C \x{263a} Unicode(smiley) \N{Name} Named Character

Escape characters cont. \N{Name} is mainly used in denoting UNICODE characters by as they cant be typed using standard keyboards we use. \u - Force next character to uppercse  \l - Force next character to lowercase  \U - Force all following characters to uppercase  \L - Force all following characters to lowercase  \Q - backslash all following nonalphanumeric characters  \E - end \U,\L and \Q 

Single and double quotes   

$a = 'apples'; $b = 'bananas'; print $a . ' and ' . $b; −

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print '$a and $b \n'; −

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prints: apples and bananas prints: $a and $b \n

print "$a and $b \n"; −

prints: apples and bananas followed by a newline

Single Quotes

Backquotes (`) will execute an external program and return the output of the program,so that it can be captured as a single string containing all the lines of output. Example$cwd =`pwd`; #string output from a command

Variables naming Naming convention Unlike C or Java, Perl variables don't have to be declared before being used. Variables are created when it's 1st used. They are identified by the "funny characters" that precede them. 

Since reserved words and filehandles are not preceded by a 'funny character', variable names will not conflict with reserved words or filehandles. 

A variable name starts with a letter, it may consist of any number of letters (an underscore counts as a letter) and/or digits. 

Types Perl has mainly these three data types -

$cents @large %interest

-

Type

Symbol

Scalar Array Hash

$ @ %

An individual value (number or string) A list of values, keyed by number A group of values, keyed by string

Scalars

Scalar variables can be assigned any form of scalar value: integers,floating-point numbers, strings, and even eferences to other variables, or to objects.

Example:-

$answer = 42; $pi = 3.14159265; $avocados = 6.02e23;  $pet = "Camel"; $fido = new Camel "Fido";

 # an integer  # a "real" number # scientific notation  # string  # an object

Array An array is an ordered list of scalars, accessed by the scalar's position in the list.  The list may contain numbers, or strings,or a mixture of both.  As in C the array indexes start from 0.  Array subscripts are enclosed in square brackets. 

Example@array = ("couch", 16, 35.68, "32");

Assignments can also be written as$array[0] = "couch"; $array[1] = 16; $array[2] = 35.68; $array[3] = "32";

Operation on Array Some commonly used built-in functions:  push ­adds new elements to the end of array  pop - removes last element  shift - removes first element  unshift - adds new elements to the beginning of the array  splice - removes or adds elements from some position in the array  sort - sorts the elements of an array  reverse – returns reversed elements from a given array

Operations on array cont. 

push (@food, "eggs", "bread"); −

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push returns the new length of the list

$sandwich = pop(@food); $ret  = shift @food;

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unshift(@food,"sandwich","cake");

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@discarded=splice(@food,2,2);

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@sorted = sort(@food);

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@reversed=reverse(@food);

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$len = @food;  #$len gets length of @food $#food  #returns index of last element

split 

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split breaks a string into parts $info = "Caine:Michael:Actor:14, Leafy  Drive"; @personal = split(/:/, $info); @personal =     ("Caine", "Michael", "Actor", "14,  Leafy Drive");

Lists and arrays

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Double dot(..) operator for generating numbers

@x = (1..6); # same as (1, 2, 3, 4, 5, 6) @z =(2..5,8,11..13);#same as (2,3,4,5,8,11,12,13) qw() "quote word" function qw(Jan Piet Marie) is a shorter notation for ("Jan","Piet","Marie").

Hash

A hash is an unordered set of scalars, accessed by some string value that is associated with each scalar. For this reason hashes are often called "associative arrays". Example %longday = (     "Sun" => "Sunday",     "Mon" => "Monday",     "Tue" => "Tuesday",     "Wed" => "Wednesday",     "Thu" => "Thursday",     "Fri" => "Friday",     "Sat" => "Saturday", );

Operations on Hash 

To get the value with key Wed we use $longday{"Wed"}

Some operations on hash    

keys - retrieves all the keys in a hash values - retrieves all the values in a hash each - retrieves a key/value pair from a hash delete - removes a key/value pair

Operations on Hash cont.  @keys=keys(%longday); return array of keys in random order.

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@values=values(%longday); return array of values in random order.

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($key,$value)=each(%weekday); returns, in random order, a two-element array whose elements are the key and the corresponding value of a hash. 

 $del=delete $weekday{"Fri"}; delete a value from %weekday and return it if successful

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Scope

In Perl scripts, the variable is visible to the entire script and can be changed anywhere within the script. Using our, local, and my functions in packages, it is possible to change the scope and namespace of a variable.

Operators Associ Operators Description ativity left terms and list operators These include variables, quote and quotelike operators, any expression in parentheses, and any function whose arguments are parenthesized left -> Infix dereference operator. ++ Auto-increment. -Auto-decrement. right ** Exponentiation. right \ Reference to an object (unary). right

!

~

Unary negation, bitwise complement.

right

+

-

left

=~

left

!~

Unary plus, minus. Binds a scalar expression to a pattern match. Same, but negates the result.

Operators cont. Associa Operators tivity left * / % x left + - . left >> << named unary operators < > <= >= lt gt le ge == != <=> eq ne cmp left left left left

& | ^ && ||

Description Multiplication, division, modulo, repetition. Addition, subtraction, concatenation. Bitwise shift right, bitwise shift left. E.g. sleep, sqrt, -r, -e. Numerical relational operators. String relational operators. Numerical equal, not equal, compare. Stringwise equal, not equal, compare.

Compare operators return -1 (less), 0 (equal) or 1 (greater).

Bitwise AND. Bitwise OR, exclusive OR. Logical AND. Logical OR.

Operators cont. Associa tivity

Operators

left

..

right

?:

right

= += -= *= etc.

Description In scalar context, range operator. In array context, enumeration. Conditional (if ? then : else) operator.

right

Assignment operators. Comma operator, also list element , separator. Same as comma, but enforces the left => operand to be a string. The right side of a list operator governs list operators(rightward) all the list operator's arguments not Low precedence logical NOT.

left

and

left

or xor

left left

Low precedence logical AND. Low precedence logical OR, exclusive OR.

Arithmetic in Perl $a = 1 + 2;   # Add 1 and 2 and store in $a $a = 3 ­ 4;   # Subtract 4 from 3 and store in $a $a = 5 * 6;   # Multiply 5 and 6 $a = 7 / 8;   # Divide 7 by 8 to give 0.875 $a = 9 ** 10; # Nine to the power of 10,ie., 910 $a = 5 % 2;   # Remainder of 5 divided by 2 ++$a;         # Increment $a and then return it $a++;         # Return $a and then increment it ­­$a;         # Decrement $a and then return it $a­­;         # Return $a and then decrement it

String and assignment operators $a = $b . $c;   # Concatenate $b and $c $a = $b x $c;   # $b repeated $c times $a = $b;        # Assign $b to $a $a += $b;       # Add $b to $a $a ­= $b;       # Subtract $b from $a $a .= $b;       # Append $b onto $a

Conditional checks Perl provides mainly two kinds of conditional checks if condition and a its variant if..elsif condition. Perl has no boolean data type. Anything that evaluates to the null string,undefined variable ,the number zero or the string "0" is considered false, everything else is true (including strings like "00"!).

if statement

Syntax:if (Expression) {Block} if (Expression) {Block} else {Block}

if statements if ($a) { print "The string is not empty\n"; } else { print "The string is empty\n"; }

if-elsif

Syntax: if (Expression) {Block} elsif (Expression) {Block}... else {Block}

if - elsif statements if (!$a)    { print "The string is empty\n"; } elsif (length($a) == 1)   { print "The string has one  character\n"; } elsif (length($a) == 2)   { print "The string has two  characters\n"; } else    { print "The string has many  characters\n"; }

Loop Structures while(Expression){Block} until (Expression) {Block} do {Block} while (Expression); do {Block} until (Expression); for (Expression1;Expression2;Expression3) {Block} foreach VARIABLE (ARRAY) {BLOCK}

Break / continue

Stop a loop, or force continuation: last; # C break next; # C continue

while loops #!/usr/local/bin/perl print "Password? "; $a = <STDIN>; chop $a;     # Remove the newline at end while ($a ne "fred") {     print "sorry. Again? ";          $a = <STDIN>;     chop $a; }

Until

The until statement executes the block as long as the control expression after the until is false, or zero. When the expression evaluates to true (nonzero), the loop exits.

Until example

until ($answer eq "yes"){        sleep(1);        print "Are you o.k. yet? ";        chomp($answer=<STDIN>); }

do..while loops #!/usr/local/bin/perl do {        print "Password? ";         $a = <STDIN>;         chop $a; }while ($a ne "fred");

do..until loop

#!/usr/local/bin/perl do { $a=<>; print $a,"\n"; }until($a==1);

for loops 

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for loops are just as in C or Java for ($i = 0; $i < 10; ++$i) {         print "$i\n"; }

foreach #Visit each item in turn and call it  $morsel foreach $morsel (@food) {         print "$morsel\n";           print "Yum yum\n";  }

Pattern Matching The s/// operator modifies sequences of characters Substitute The tr/// operator changes individual characters. Translation The m// operator checks for matching (or in short //) Matching The first part between the first two slashes contain a search pattern  The second part between two final slashes contain the replacement  Behind the final slash are characters to modify the behavior of the commands.(modifiers) 

By default s/// only replaces the first occurrence of the search patten

Pattern Matching cont. s/// and m// accepts the following modifiers-

Modifier Meaning g i m s x o

Replace every occurrence Do case-insensitive pattern matching. Treat string as multiple lines (^ and $ match internal \n). Treat string as single line (^ and $ ignore \n, but . matches \n). Extend your pattern's legibility with whitespace and comments. Compile pattern once only

Quantifier Meaning + ? * {N,M}

Matches the preceding pattern element one or more times. Matches zero or one times. Matches zero or more times. Denotes the minimum N and maximum M match count. {N} means exactly N times; {N,} means at least N times.

Basic pattern matching 

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$sentence =~ /the/ − True if $sentence contains "the" $sentence = "The dog bites."; if ($sentence =~ /the/)  # is false −

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…because Perl is case-sensitive !~ is "does not contain"

RE special characters .

# Any single character except a newline

^

# The beginning of the line or string

$

# The end of the line or string

*

# Zero or more of the last character

+

# One or more of the last character

?

# Zero or one of the last character

RE examples ^.*$

# matches the entire string

hi.*bye # matches from "hi" to "bye" inclusive x +y

# matches x, one or more blanks, and y

^Dear # matches "Dear" only at beginning bags?

# matches "bag" or "bags"

hiss+

# matches "hiss", "hisss", "hissss", etc.

Square brackets [qjk]

# Either q or j or k

[^qjk]

# Neither q nor j nor k

[a-z]

# Anything from a to z inclusive

[^a-z]

# No lower case letters

[a-zA-Z] # Any letter [a-z]+

# Any non-zero sequence of # lower case letters

More examples [aeiou]+

# matches one or more vowels

[^aeiou]+ # matches one or more nonvowels [0-9]+

# matches an unsigned integer

[0-9A-F]

# matches a single hex digit

[a-zA-Z]

# matches any letter

[a-zA-Z0-9_]+ # matches identifiers

More special characters \n \t \w \W \d \D \s \S \b \B

# A newline # A tab # Any alphanumeric; same as [a-zA-Z0-9_] # Any non-word char; same as [^a-zA-Z0-9_] # Any digit. The same as [0-9] # Any non-digit. The same as [^0-9] # Any whitespace character # Any non-whitespace character # A word boundary, outside [] only # No word boundary

Match

m/Good morning/ /Good evening/ /\/usr\/var\/adm/ m#/usr/var/adm# m(Good evening) m'$name'

Substitution s/old/new/; s/old/new/i; s/old/new/g; s+old+new+g; s(old)/new/; s[old]{new}; s/old/expression to be evaluated/e; s/old/new/ige; s/old/new/x;

Transliterate The tr/// operator allows the modification of character tr does character-by-character translation tr returns the number of substitutions made c(replaces the complement of each the search class,anything not in first spec is replaced by second,uses last character of string) s(squeeze sequences of identical replaced character to one character $sentence =~ tr/abc/edf/; − replaces a with e, b with d, c with f  $count = ($sentence =~ tr/*/*/); − counts asterisks  tr/a-z/A-Z/; − converts to all uppercase 

Examples # replace first occurrence of "bug" $text =~ s/bug/feature/; # replace all occurrences of "bug" $text =~ s/bug/feature/g; # convert to lower case $text =~ tr/[A-Z]/[a-z]/; # delete vowels $text =~ tr/AEIOUaeiou//d; # replace nonnumber sequences with a single x $text =~ tr/[0-9]/x/cs; # replace each capital character by CAPS $text =~ s/[A-Z]/CAPS/g;

End 1st part