Perl Examples

Example 1:

This program is stored in file perl-1

#!/usr/bin/perl

# Comments are written by having # as the first character of the line

# Note the name of this program is perl-1

# To execute this program type: perl perl-1

# Note perl statements end with semi colon(;).

#As is the case with C and C++ \n means empty the buffer

print "How are you\n";

Execution of the program:

perl perl-1

How are you

Example 2:

The program is stored in file perl-2

#!/usr/bin/perl

print "Enter hexadecimal number: ";

# Following statement assigns whatever typed from the keyboard i.e. the

# standard input device <STDIN> to the scalar variable answer. Notice that

# a scalar variable is a variable contains a single value. In other words

# a variable which is not an array. A scalar variable(such as $answer in

# the next statement) is made of $ sign followed by a name. A scalar

# variable can have a string or a numeric value.

$answer=<STDIN>;

# The hex in the following statement is a built-in function converts

# the hexa-decimal number to decimal number

print hex($answer),"\n";

Execution of the program:

perl perl-2

Enter hexadecimal number: 3B

Example 3:

The program is stored in file perl-3

#!/usr/local/bin/perl -w

# Notice the option -w after perl provides the ability to execute the

# program by writing its name only. Therefore to execute this program all

# all you have to do is to type perl-3 . If option -w does not follow perl you have

# to type perl perl-3 to execute perl-3 program

# perl like other shell programs recognizes all four different types

# of quotes namely back quotes, double quotes, single quotes and back

# slash quote

# The following statement executes date command and assigns its value

# to the scalar variable tday.

$tday = `date`;

# double quotes allow variable substitution

print " Welcome today date is $tday ";

# Do the following loop forever Until a control c is typed to interrupt the program

for (;;)

{

# Get the information from the user.

# Notice my in the following statement tells perl that scalar variable

# $name is a local variable.

my $name = ""; # assign null as the value for scalar variable $name

# Following while loop forces the user to enter a non null name

while ($name eq "" ) {

print "Enter a non blank employee name: ";

$name = <STDIN>;

chomp $name; # this commands removes the end line character

} end of while loop

my $hours = 0;

# repeat the loop until value greater than 0 is typed

while ($hours <= 0) {

print "Enter number of hours greater than 0: ";

$hours = <STDIN>; chomp $hours; # Notice 2 statements written on this line

}

my $rate = 0;

while ($rate <= 0) {

print "Enter rate per an hour greater than 0: ";

$rate = <STDIN>; chomp $hours;

}

# Find pay.

my $pay = $hours * $rate;

print " $name worked $hours hours at rate $rate\n";

# Notice the back slash quote in-front of $pay makes the dollar sign

# to be printed in-front of value of $pay

print "The pay for $name is \$$pay \n";

}

Execution of the program:

perl-3

Welcome today date is Sun Mar 5 23:52:48 EST 2000

Enter a non null employee name: Linda Brown

Enter number of hours greater than 0: 38

Enter rate per an hour greater than 0: 10.50

Linda Brown worked 38 hours at rate 10.50

The pay for Linda Brown is $399

Enter a non null employee name: Jim Smith

Enter number of hours greater than 0: 20

Enter rate per an hour greater than 0: 10

Jim Smith worked 20 hours at rate 10

The pay for Jim Smith is $200

Enter a non null employee name:

% cat perl-4-list

#!/usr/local/bin/perl -w

# Declare an array months. Notice the character @ before months. This

# tells perl that months is an array.

# my tells perl that this is a local variable. Perl 4 had "local"

# Instead of "my" to declare local variables. Perl 5 accepts both

# my and local to declare local variables. It is recommended to use my.

# "qw" (stands for quote word) makes perl to consider the entries

# between parentheses to be quoted.

# Without qw the above statement should be written as:

# my @months = ("JUNK" "Jan" "Feb" "March" "April" "May" "June" # "July" "Aug" "Sept" "Oct "Nov" "Dec");

# The index of the array and list starts at 0. As you see the following

# Statement declares an array of size 13 and initializes its elements. The

# value of the first element $months[0] is Junk and the value of

# $months[12] is Dec.

my @months = qw (JUNK Jan Feb March April May June July Aug Sept Oct Nov Dec);

# Declare and initialize the value of scalar variable (that is non array

# variable) x to 0.

my $x = 0;

# Use the for loop to print out the contents of the array.

#Notice the # after $ sign in-front of the array name month in the for

#statement below. The $#months is the index of the last element of the array

for ($x=0; $x <= $#months; $x++)

{

# Notice the $ in-front of months, That tells retrieve the value of months

print "Index[$x] = $months[$x]\n";

}

Following is the execution of perl-4-lits

Execution of the program:

perl-4-list

Index[0] = JUNK

Index[1] = Jan

Index[2] = Feb

Index[3] = March

Index[4] = April

Index[5] = May

Index[6] = June

Index[7] = July

Index[8] = Aug

Index[9] = Sept

Index[10] = Oct

Index[11] = Nov

Index[12] = Dec

cat perl-4-v2

#!/usr/local/bin/perl -w

# Following statement declars an array ar. Numbers between 20 to 25 are

# assigned to its elements

my @ar = (20..25);

print "the elements of the array area:\n";

#The next statement prints all elements of the array. Notice no subscript

# after @ar

print "@ar\n";

# Assign the size of the array to scalar variable $n. In this case the

# value of $n will be 6.

$n=@ar;

print "\narray size is $n";

# Assign the index of the last element $#ar (in this case is 5) to the

# scalar variable $n2

$n2=$#ar;

print "\nthe index of the last elemn is $n2";

# Because the index of the first elemnt is 0, the size of the array equal

# to the index of the last elemnt + 1

$array_size=$n2 +1;

print "\narray size also is $array_size\n";

Execution of the program:

% cat perl-5

#!/usr/local/bin/perl -w

# File_input contain 5 numbers each on a line.

$Infile="File_input"; # This statement assigns file handler Infile to File_input

open (Infile);

# Next statement declares Inarray as an array and assigns the records of Infile to the array-elements

@Inarray =<Infile>;

close (Infile);

# Next statement assigns the size of the array to scalar variable $arsize

my $arsize = @Inarray; # Note array name without subscript means the size of the array.

print "number of elements in the array is: $arsize \n";

print "number of elements in the array is: ", $#Inarray + 1, "\n";

foreach $i (@Inarray) {

print "$i";

}

Execution of the program:

% cat perl-5-v2

#!/usr/local/bin/perl -w

#define array @array and scalar variable index

my (@array, $index);

# Push the elements on the 'stack'

push (@array, "Hello");

push (@array, "World!");

# Print out the contents of the array using foreach loop.

foreach (@array)

{

# Notice $_ is a special variable for default input. perl has 50 special

# variables. Also there are English name for them. For example $$ is the

# processor id. But if you use the English module (by having use English;

# as a statement in your program you can use English names.

print "Foreach loop: $_\n";

}

# Print out the contents of the array via pop.

while ( $index = pop(@array) )

{

print "Popping off stack: $index\n";

}

Execution of the program:

cat perl-6-stack

#!/usr/local/bin/perl -w

# Define variables.

my ($index, @mylist);

# Push the elements onto the stack.

push (@myList, "you?");

push (@myList, "are");

push (@myList, "how");

push (@myList, "world!");

push (@myList, "Hello");

while ($index = pop(@myList))

{

print "Popping off stack: $index\n";

}

Execution of the program:

perl-6-stack

Popping off stack: Hello

Popping off stack: world!

Popping off stack: how

Popping off stack: are

Popping off stack: you?

cat perl-7-each

#!/usr/local/bin/perl -w

# Create an Associative array call it mySchools. Notice character "%"

# before the name makes the name to be an Associative array.

# Associative arrays (also known as hash arrays) do not have beginning

# and end. Keys reference the individual values of the array elements.

# Notice the ke and its associated value either separated by => or a comma ,

# Notice the key Kurdistan _ High School and its associated value Erbile are separated by a comma

my %mySchools = ("Kurdistan_Elm" => Rawanduz, "Kurdistan _ High School",

Erbile, "Iraq" => "Baghdad University", "US - ST. Louis" => "Washington University");

# The following statement displays the value of the array

# element referenced by key Kurdistan_Elm. Notice that the key is in braces

# Notice curly parenthesis around key

print "The school identified by key Kurdistan_Elm is: $mySchools{Kurdistan_Elm}\n";

my ($key, $value);

# Print out the contents of the hash.
while (($key, $value) = each %mySchools)

{

print "Key: $key Value: $value \n ";

}

Execution of the program:

Bellow is the execution of the program

perl-7-each

The school identified by key Kurdistan_Elm is: Rawanduz

Key: Kurdistan_Elm Value: Rawanduz

Key: Kurdistan _ High School Value: Erbile

Key: Iraq Value: Baghdad University

Key: US - ST. Louis Value: Washington Universi

cat perl-8-key-2

#!/usr/local/bin/perl -w

# Create an Associative array call it mySchools. Notice character "%" before the name.

my %mySchools = ("Kurdistan -Elm" => Rawanduz, "Kurdistan _ High School",

Erbile, "Iraq" => "Baghdad University", "US - ST. Louis" => "Washington University");

# declare key as a scalar variable. Notice both word keys and values are reserved

# words in perl, but key and value are not.

my $key;

# Print out the contents of the hash. Notice the sort keys.

for $key (sort keys %mySchools)

{

print "Key: $key Value: $mySchools{$key} \n";

}

Execution of the program:

Bellow is the execution of the program

perl-8-key-2

Key: Iraq Value: Baghdad University

Key: Kurdistan -Elm Value: Rawanduz

Key: Kurdistan _ High School Value: Erbile

Key: US - ST. Louis Value: Washington University

cat perl-9-value

#!/usr/local/bin/perl -w

# Create an Associative array call it mySchools. Notice character "%" before the name.

my %mySchools = ("Kurdistan -Elm" => Rawanduz, "Kurdistan _ High School",

Erbile, "Iraq" => "Baghdad University", "US - ST. Louis" => "Washington University");

my $value;

# Print out the contents of the hash. Notice the sort in-front of values

for $value (sort values %mySchools)

{

print "Value: $value \n";

}

Execution of the program:

Bellow is the execution of the program

perl-9-value

Value: Baghdad University

Value: Erbile

Value: Rawanduz

Value: Washington University

cat perl-10

#!/usr/local/bin/perl -w

# To end the execution of this program type control c

# Do this forever

for (;;)

{

# Get the information from the user.

print "Enter a number: ";

my $num1 = <STDIN>; chomp $num1;

print "Enter another number: ";

my $num2 = <STDIN>; chomp $num2;

# Perform some basic operations.

my $sum = $num1 + $num2;

my $diff = $num1 - $num2;

print "The sum of $num1 and $num2 is $sum\n";

print "The difference of $num1 and $num2 is $diff\n";

if ($num1 = = $num2)

{ print "Both numbers are equal.\n"; }

if ($num1 < $num2)

{ print "<$num1> is numerically less than <$num2>\n"; }

if ($num1 > $num2)

{ print "<$num1> is numerically greater than <$num2>\n"; }

}

Execution of the program:

Bellow is the execution of the program

perl-10

Enter a number: 30

Enter another number: 60

The sum of 30 and 60 is 90

The difference of 30 and 60 is -30

<30> is numerically less than <60>

Enter a number:

Cat perl-10-v2

#!/usr/local/bin/perl -w

# To end the execution of this program type control c

# Do this forever

# The following statement is a label, which includes an infinite for loop

FOREVER_LOOP:

for (;;)

{

# Get the information from the user.

print "To stop the program type 99999\n";

print "Enter a number: ";

my $num1 = <STDIN>; chomp $num1;

# Exit from FOREVER_LOOP if 99999 is type

last FOREVER_LOOP if $num1 == 99999;

print "Enter another number: ";

my $num2 = <STDIN>; chomp $num2;

# Perform some basic operations.

my $sum = $num1 + $num2;

my $diff = $num1 - $num2;

print "The sum of $num1 and $num2 is $sum\n";

print "The difference of $num1 and $num2 is $diff\n";

if ($num1 = = $num2)

{

print "Both numbers are equal.\n";

}

if ($num1 < $num2)

{

print "<$num1> is numerically less than <$num2>\n";

}

if ($num1 > $num2)

{

print "<$num1> is numerically greater than <$num2>\n";

}

}

Execution of the program:

Bellow is the execution of the program

perl-10-v2

To stop the program type 99999

Enter a number: 40

Enter another number: 40

The sum of 40 and 40 is 80

The difference of 40 and 40 is 0

Both numbers are equal.

To stop the program type 99999

Enter a number: 99999

cat perl-10-annonymous-array

#!/usr/local/bin/perl -w

# Create the anonymous array reference.

# Notice anonymous arrays are created by enclosing a set of values

# between [ and ] without having any name to the arrays.

my $arrayRef = [[1,2,3,4], 'a', 'b', 'c', 'd', 'e', 'f'];

# Print out some of the array

# Remember the dot . is for concatination

print $arrayRef->[0][0] . "\n";

print $arrayRef->[0][2] . "\n";

print $arrayRef->[0][1] . "\n";

print $arrayRef->[0][3] . "\n";

print "reference to the first element :";

# The following statement prints the reference to the first element,

# because the first element itself is an array.

print $arrayRef->[0] . "\n";

# print all elements of the first array

for ($i=0; $i<4; $i++)

{

print $arrayRef->[0][$i] ." " ;

}

#print all elements of the anonymous array arrayRef

print "\narrayRef elements are:\n";

for ($i=0; $i<8; $i++)

{

print $arrayRef->[$i] . " " ;

}

print "\n";

Execution of the program:

Bellow is the execution of the program

perl-10-annonymous-array

reference to the first element :ARRAY(0x140002080)

1 2 3 4

arrayRef elements are:

ARRAY(0x140002080) a b c d e f

Example -11

cat grade-perl

#!/usr/local/bin/perl -w

# open a file called grades and assign GRADES as the file handle for it

# if the file does not exist the program calls function die that

# prints the message and terminate the program. Note or is a short circuit

# logical operator. That is if first operand is executed successfully the

# rest of the command is skipped.

# The value of $! will contains the error message if it can not open the file

# Notice < in grades indicates to open grades as an input file

open(GRADES, "<grades") or die "can not open grades: $!\n";

# <GRADES> returns a string value, or it fails when there are no

# more lines in the file. On the failure, $line is undefined. the

# "defined()" function returns true if $line has a good value,

# and returns false if $line is undefined. While statement requires

# true or false value, defined stands for true and undefined is for false

while ( defined($line = <GRADES>) ) {

# Fields of $line are separated by spaces

($student, $grade) = split (" ", $line);

# Notice the period before = and after $grade means concatenation.

# The following statement makes grades to be an associate array (%grades),

# The key will be $student, because $Student follows $grades and

# is enclosed in curly braces

$grades{$student} .= $grade . " ";

} # End of while loop

foreach $student (sort keys %grades) {

# number of grades of a student will be assigned to scalar variable

# $scores and $total will contains sum of grades of a student

$scores = 0;

$total = 0;

# The next statement creates an ordinary array grades (@grades). Thus

# thus we have associate array %grades and ordinary array @array'

@grades = split (" ", $grades{$student});

# Following foreach loop finds number of grades and sum of grades for

# a student

foreach $grade (@grades) {

$total += $grade;

$scores++;

} # End foreach loop

# Find the average grade for a students

$average = $total / $scores ;

print "$student: $grades{$student}\tAverage: $average\n";

}

Execution of the program:

Following is the content of grades file

cat grades

Noel 25

Ben 76

Clem 49

Norm 66

Chris 92

Doug 42

Carol 25

Ben 24

Clem 51

Norm 66

Clem 92

Noel 75

Noel 80

Clem 38

Bellow is the execution of the program

grade-perl

Ben: 76 24 Average: 50

Carol: 25 Average: 25

Chris: 92 Average: 92

Clem: 49 51 92 38 Average: 57.5

Doug: 42 Average: 42

Noel: 25 75 80 Average: 60

Norm: 66 66 Average: 66

Example -11-V2

In this version unless is used with die function and $#grades +1 to find number of elements in an array. The rest of the program is identical to the previous version.

cat grade-perl-v2

#!/usr/local/bin/perl -w

# This version of grades use die and unless statements

# The following statement display message can not open grades unless

# grades file is exist.

die "can not open grades: $!\n"

unless (open(GRADES, "<grades"));

while ( defined($line = <GRADES>) ) {

($student, $grade) = split (" ", $line);

$grades{$student} .= $grade . " ";

}

foreach $student (sort keys %grades) {

$total = 0;

@grades = split (" ", $grades{$student});

foreach $grade (@grades) {

$total += $grade;

}

#Notice $#grades is the index of the last element of the array

$average = $total / ($#grades + 1) ;

print "$student: $grades{$student}\tAverage: $average\n";

}

cat perl-12

#!/usr/local/bin/perl -w

# Do this forever

for (;;)

{

# Get the information from the user.

print "Enter a word: ";

my $word1 = <STDIN>; chomp $word1;

print "Enter another word: ";

my $word2 = <STDIN>; chomp $word2;

# Perform some basic operations.

if ($word1 eq $word2)

{

print "The two phrases are equivalent.\n";

}

if ($word1 lt $word2)

{

print "<$word1> is alphabetically less than <$word2>\n";

}

if ($word1 gt $word2)

{

print "<$word1> is alphabetically greater than <$word2>\n";

}

Execution of the program:

Bellow is the execution of the program

perl-12

Enter a word: Jim

Enter another word: Kim

<Jim> is alphabetically less than <Kim>

Enter a word:

perl-13-ref

#!/usr/local/bin/perl -w

# Set up the data types.

my $scalarVar = "How are you doing?";

my @arrayVar = qw (January February March April May);

my %hashVar = ('Pay-type' => 'regular', 'Rate' => 23.5, 'Union' => No);

# Reference variables are created by having \ in-front of the variables

# Create the references

my $scalarRef = \$scalarVar;

my $arrayRef = \@arrayVar;

my $hashRef = \%hashVar;

# Notice reference variables are pointers in languages such as C or C++

# Print out the references.

print "$scalarRef \n";

print "$arrayRef \n";

print "$hashRef \n";

# To create de-reference:

# Put $ in-front of reference variable to a scalar variable.

# Put @ in-front of reference variable to an array.

#Put % in-front of reference variable to a hash array.

# Print the content of variable referenced by scalar variable.

print "scalar value: $$scalarRef \n";

#Print the content of the elements of the array referenced by

# reference variable

my $month;

for $month (@$arrayRef)

{

print "Month: $month \n";

}

#print the content of the elements of the hash array referenced by

# reference variable

my $hashelement;

for $hashelement (%$hashRef)

{

print " $hashelement \n";

}

print "Sorted keys:\n";

for $hashelement (sort keys %$hashRef)

{

print " $hashelement\n";

}

print "Sorted values:\n";

for $hashelement (sort values %$hashRef)

{

print " $hashelement\n";

}

Execution of the program:

Bellow is the execution of the program

perl-13-ref

SCALAR(0x140010160)

ARRAY(0x1400101b0)

HASH(0x140010210)

scalar value: How are you doing?

Month: January

Month: February

Month: March

Month: April

Month: May

Union

Pay-type

regular

Rate

23.5

Sorted keys:

Pay-type

Rate

Union

Sorted values:

23.5

regular

How To Simulate Case-Switch statements in perl

perl does not have case or switch statements. However these statements can be simulated in many ways in perl. Following is an example of simulating a case statement by creating a label. This example is taken from your text book on page 198.

cat perl_case_simulate-2

#!/usr/local/bin/perl -w

# This program to be executed as:

# perl_case_simulate /A/C /HELP /B /Foo/Bar:3

$Args = ""; # assign null to scalar variable $Args

# Notice @ARGV is a reserved array that contains all arguments submitted

# with the program. In this case @ARGV[0]= /A/C , @ARGV[1]= /HELP ,

# @ARGV[2]= /B , and @ARGV[3]= /Foo/Bar:3

# Notice arguments were seprated by spaces

# Notice in the Following while loop @ARGV is size of the

# of the array @ARGV and the while loop is executed as long as

# the size of the array is greater than 0.

while (@ARGV) {

#Usually to search for a pattern the pattern is enclosed

# between / and / . Notice the character m in the expression =~ m%^/%

# tells perl that the next character is (that is %) used for search instead of usual /

# Character ~ tells match the expression on the left of = sign

$ARGV[0] =~ m%^/% || last;

# Notice shift uses @ARGV by defaut

$Args .= shift;

# Following are the values of $Args during the execution of while loop

# At the end of first iteration: value of $Args is /A/C

# At the end of second iteration: value of $Args is /A/C/HELP

# At the end of third iteration: value of $Args is /A/C/HELP/B

# At the end of final iteration: value of $Args is /A/C/HELP/B/Foo/Bar:3

} # end of while loop

# The following statement deletes the first / from $Args

# Notice character s stands for subsitute

$Args =~ s%^/%%;

# now value of $Args is A/C/HELP/B/Foo/Bar:3

foreach $Arg (split("/",$Args)) {#Begun foreach

# the expression \w+ takes all alphanumeric characters until

# a non alphanumeric is found. Thus the string will be A

$Arg =~ /\w+/;

#Notice $& is the string from the last successful pattern match

$_ = $&;

CASE: { #begin case

# case A

/^A$/ && do {

print "Found A\n";

last CASE;

};

# case B

/^B$/ && do {

print "Found B\n";

last CASE;

};

# case C

/^C$/ && do {

print "Found C\n";

last CASE;

};

# case HELP

/^HELP$/ && do {

print "Found HELP\n";

last CASE;

};

# case None of the above

print "Unknown option found: /$Arg\n";

} # End CASE

} # End foreach