PERL Ronald L. Ramos Proglan

What is PERL? Perl stands for Practical Extraction and Reporting Language. (or Pathologically Eclectic Rubbish Lister). Perl is a general-purpose, high level, interpreted and dynamic computer programming language with a vast number of uses. PERL is a language for doing what you want to do

PERL Strengths Perl runs on all platforms and is far more portable than C. Perl and a huge collection of Perl Modules are free software (either GNU General Public License or Artistic License). Perl is very much efficient in TEXT and STRING manipulation i.e. REG_EXP. It is a language that combines the best features from many other languages and is very easy to learn if you approach it properly. Dynamic memory allocation is very easy in PERL, at any point of time we can increase or decrease the size of the array.

PERL Weaknesses 1) You cannot easily create a binary image ("exe") from a Perl file. It's not a serious problem on Unix, but it might be a problem on Windows. 2) Moreover, if you write a script which uses modules from CPAN, and want to run it on another computer, you need to install all the modules on that other computer, which can be a drag. 3) Perl is an interpretative language, so its comparatively slower to other compiling language like C. So, it s not feasible to use in Real time environment like in flight simulation system.

Hello World print "Hello World!\n";

VARIABLES

Scalar Variables Scalar data is the one of the most basic and simplest data in Perl. Scalar data can be number or string. In Perl, string and number can be used nearly interchangeably. Scalar variables are used to hold scalar data. Scalar variables start with dollar sign ($) followed by Perl identifier. Perl identifiers can contain alphanumeric characters and underscores. You cannot start with a digit.

Numbers #floating-point values $x = 3.14; $y = -2.78; #integer values $a = 1000; $b = -2000; Perl also accepts string literal as a number for example: $s = "2000"; # similar to $s = 2000;

String $str = "this is a string in Perl“; $str2 = 'this is also as string too‘;

Operations on Scalars $x = 5 + 9; # Add 5 and 9, and then store the result in $x $x = ;# Subtract 4 from 30 # and then store the result in $x $x = 3 * 7; # Multiply 3 and 7 and then store the result in $x $x = 6 / 2; # Divide 6 by 2 $x = 2 ** 8;# two to the power of 8 $x = 3 % 2; # Remainder of 3 divided by 2 $y = ++$x; # Increase $x by 1 and store $x in $y $y = $x++; # Store $x in $y then increase $x by 1 $y = --$x; # Decrease $x by 1 and then store $x in $y $y = $x--; # Store $x in $y then decrease $x by 1 $x = $y; # Assign $y to $x $x += $y; # Add $y to $x $x -= $y; # Subtract $y from $x $x.= $y; # Append $y onto $x

String Operations $x = 3; $c = "he "; $s = $c x $x; $b = "bye"; # $c repeated $x times print $s. "\n"; #print s and start a new line # similar to print "$s\n"; $a = $s. $b; # Concatenate $s and $b print $a;

Scalar Interpolation $x = 10; $s = "you get $x"; print $s;

CONTROL STRUCTURES

Code blocks A block is surrounded by a pair of curly braces and can be nested within a block: { #statements here { # nested block # statements here }

If If control structure is used to execute a block of code based on a condition. The syntax of If control structure is as follows: if(condition){ statements; } If the condition is true the statements inside the block will be executed, for example: $x = 10; $y = 10; if($x == $y){ print "$x is equal to $y"; }

If Else If you need an alternative choice, Perl provides if-else control structure as follows: if(condition){ if-statements; } else{ else-statements; }

If Else If the condition is false the else-statements will be executed. Here is the code example: $x = 5; $y = 10; if($x == $y){ print "x is equal to y"; } else{ print "x is not equal to y"; }

If Else If Perl also provides if-else-if control structure to make multiple choices based on conditions. if(condition1){ } else if(condition2){ } else if(condition3){ }... else{ }

If Else If Here is the source code example: $x = 5; $y = 10; if($x > $y){ print "x is greater than y"; } else if ($x < $y){ print "x is less than y"; } else{ print "x is equal to y"; }

For In order to run a block of code iteratively, you use Perl for statement. The Perl for statement is used to execute a piece of code over and over again. The Perl for statement is useful for running a piece of code in a specific number of times. The following illustrates Perl for statement syntax: for(initialization; test; increment){ statements; }

For Here is a code snippet to print a message 10 times. for($counter = 1; $counter <= 10; $counter++){ print "for loop #$counter\n"; } Perl allows you to omit the initialization and increment part of for statement. You can initialize outside the loop and increase control variable inside the block as follows: $counter = 1 for(; $counter < 10;){ print "for loop #$counter\n"; $counter++; }

While Perl While statement is a Perl control structure that allows to execute a block of code repeatedly. The Perl while statement is used when you want to check a boolean condition before making a loop. The following illustrates the Perl while statement syntax: while(condition){ #statements; }

While $x = 0; while($x < 5){ print "$x\n"; $x++; }

Do While Beside while loop, Perl also provides do while loop statement. do while loop statement is similar to while loop but it checks the loop condition after executing the block therefore block executes at least one time. Here is a code snippet to demonstrate do while statement: $x = 0; do{ print "$x\n"; $x++; }while($x < 5);

ARRAYS

Lists Scalar variable allows you to store single element such as number or string. When you want to manage a collection or a list of scalar data you use list. Here are some examples of lists. ("Perl","array","tutorial"); (5,7,9,10); (5,7,9,"Perl","list"); (1..20); ();

Array Variables To store lists of values to use throughout your program you need array variables. Array variable is used to hold a list of data. Different from scalar variables, array variables are prefixed with the at For example we have five array variables to store five lists above as = = = = = ();

Operations on Arrays Here is the code snippet to demonstrate each function =(1,3,5,2); #add 10 print $last = #remove 10 print #add 0 print $start = # add 0 print

Operations on Arrays You can add or remove elements to/from an array. Here is a list of common operations on arrays: add $element to the end of remove the last element of and returns it. add $element to the start of remove the first element from and returns it.

HASH

What is hash? When number of item in an array is bigger, the performance is degraded also. Perl createdhash - before that is it called associative array - to overcome this limitation. Hash is another kind of collective data type. Hash can hold as many as scalar like array but the way you accessing hash element is different. You access hash element in has by using a key.Each has element has two parts: key and value or key-value pair.

Hash The key identifies the value of element associated with it. To define a hash variable, you use percentage sign (%) as follows: %websites = ( "perltutorial.org" => "Perl tutorial", "Perl.org" => "Perl directory" );

Accesing Hash Elements To access a hash element, you use the key of that element to retrieve the value as follows: print $websites{"perltutorial.org"}; #Pe rl tutorial

Filling Hash Elements You can define hash as above example or use a list as follows: %websites = ( "perltutorial.org" => "Perl tutorial", "Perl.org" => "Perl directory" ); Another way to fill the hash element by using key-value pair and assignment operator as follows: $websites{"Perl.com"} = "Perl.com homepage"; print $websites{"Perl.com"}; #Perl.com homepage

Testing a Key To test whether a key exists in a hash, you use exist function provided by Perl. Here is the syntax: if ( exists $hash{key} ){ #retrieve value here } For example, we can test whether key "perltutorial.org" exists in %websites hash by using the above pattern: %websites = ( "Perltutorial.org","Perl tutorial", "Perl.org", "Perl directory" ); if(exists $websites{"Perltutorial.org"}){ #Perl tutorial print $websites{"Perltutorial.org"}; }

Remove a Key from Hash To remove a single key from hash, you use delete function as follows: delete $hash{key}; To remove all keys and values from a hash, you just assign hash to an empty list: %hash = ();

Looping through a hash To loop through a hash you use foreach statement. First you retrieve all keys of the hash by using keys function. Based on this list you can find all elements of the hash. Here is the syntax: foreach $element (keys %hash){ #process hash element here }

Looping through a hash For example, we can loop through %websites hash: %websites = ( "Perltutorial.org","Perl tutorial", "Perl.org", "Perl directory" ); foreach $website (keys %websites){ print "$website is about $websites{$website}\n"; } #output: #Perltutorial.org is about Perl tutorial #Perl.org is about Perl directory

Array and Hash You can assign an hash to an array and vice versa. For example: %websites = ( "Perltutorial.org" =>"Perl tutorial", "Perl.org" => "Perl directory" = %websites;

SUBROUTINES

Define a Subroutine To define subroutine you use the keyword sub followed by subroutine name and its body. Here is the syntax of subroutine definition. sub subroutine_name{ #subroutine body } For example, here is a simple subroutine to print a message. sub print_message{ print "Perl subroutine tutorial"; }

Call a Subroutine To invoke or call subroutine, you use the subroutine name with the ampersand (&) prefixed as follows: &print_message;

Parameters Parameters are passed to a subroutine as a list which is available in a subroutine as - an array variable. For example:array sub print_list{ print } #print: this is Perl subroutine tutorial &print_list("this","is","Perl","subroutine","tut orial"); #print: subroutine tutorial 8&print_list("subroutine","tutorial");

Parameters In the line 2, we printed the list variable which was the input parameters of the subroutine. In line 5 and 7, we called subroutine with different list and we got different output. You can refer to each parameter in a list by using scalar $_[index] for example: sub max{ if($_[0] > $_[1]){ $_[0]; } else{ $_[1]; } $m = max(10,20); $m2 = max(50,30); print "$m\n"; print "$m2\n";

Returning Values Subroutine returns values which is the last expression evaluated. For example : sub cal_sum{ print "sum of two numbers\n"; $_[0] + $_[1]; } $result = &cal_sum(10,20); # result is 30 print $result;

Returning Values If you want to return value immediately from subroutine, you can use returnoperator, for example: sub min{ if($_[0] < $_[1]){ return $_[0]; } else{ return $_[1]; } $m = &min(10,20); # result is 10 print $m;

Returning a List of Values Subroutine returns not only scalar value but also a list of values. Let's take a look at an example below: sub get_list{ return 5..10; = &get_list; print #

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