scripting language first unit b.tech it and cse

1. PERL NAMES,VALUES AND
VARIABLES
BY
SANA MATEEN
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2. NAMES IN PERL
 Perl manipulates variables which have a name.
 A value is assigned to/stored in variable by assignment statement of the
form
name=value
 Perl distinguishes between singular name and plural name.
A singular name –holds single item of data– scalar value
A plural name for variable – hold collection of data items —
an array or hash
 Starting special character of variable denotes the kind of thing that
name stands for
 $ ---- Scalar data
 @ ----- Array
 % ----- Hash
 & ----- Sub routine
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3. NAMES IN PERL...
 Valid characters are letters,digits,underscores.
 First character after special character can be a letter or underscore.
 Names may also have non-alphanumeric character after special character.
$$,$? (system reserved names in Perl )
 Each kind of data has separate namespace.
 Special character determine the context in which the name is being used.
 In C language a new variable is declared as
int i=1;
float data[9];
 Scope of variable depends on the part of program in which the variable is visible and
available for use.
 Global scope and local scope.
 Variable declaration in perl –
$a=5;
my $a=10;
 A variable comes into existence when declared or first used with special value denoted by
undef
undef $x;
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4. NAMES IN PERL...
 use strict ‘var’; (or) use strict;
 It tells perl to insist on declaration by placing the line.
 At the start of script variables are declared using
 my $x,$y;
#!/usr/bin/perl
@ages = (25, 30, 40);
@names = ("John Paul", "Lisa", "Kumar");
print "$ages[0] = $ages[0]n"; print "$ages[1] = $ages[1]n";
print "$ages[2] = $ages[2]n"; print "$names[0] = $names[0]n";
print "$names[1] = $names[1]n"; print "$names[2] = $names[2]n";
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5. A scalar is a single unit of data. Perl recognizes two kinds of scalar data , a String
and Numbers . There’s no difference between integers and real numbers both are
same.
Here is a simple example of using scalar variables −
#!/usr/bin/perl
$age = 25; # An integer assignment
$name = "John Paul"; # A string
$salary = 1445.50; # A floating point
print "Age = $agen";
print "Name = $namen";
print "Salary = $salaryn";
This will produce the following result −
Age = 25 Name = John Paul Salary = 1445.5
Strings are stored as sequence of bytes of unlimited length . Perl is dynamically typed
language (System keeps track of whether a variable contains a numeric value or string
value).Depending on the context strings are converted to int.
Eg:
If int/num occurs in String context, operand for string operator , perl will convert it to
string
Numeric Scalars
A scalar is most often either a number or a string. Following example demonstrates the
usage of various types of numeric scalars −
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6. #!/usr/bin/perl
$integer = 200;
$negative = -300;
$floating = 200.340;
$bigfloat = -1.2E-23;
# 377 octal, same as 255 decimal
$octal = 0377;
# FF hex, also 255 decimal
$hexa = 0xff;
print "integer = $integern";
print "negative = $negativen";
print "floating = $floatingn";
print "bigfloat = $bigfloatn";
print "octal = $octaln";
print "hexa = $hexan";
This will produce the following result −
integer = 200 negative = -300 floating = 200.34 bigfloat = -1.2e-23 octal = 255 hexa =
String Scalars
Following example demonstrates the usage of various types of string scalars.
Notice the difference between single quoted strings and double quoted strings −
#!/usr/bin/perl
$var = "This is string scalar!";
$quote = 'I m inside single quote - $var';
$double = "This is inside single quote - $var";
$escape = "This example of escape -tHello, World!";
print "var = $varn";
print "quote = $quoten";
print "double = $doublen";
print "escape = $escapen";
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7. STRING CONSTANTS/LITERALS
 String constant and literals can be enclosed in single or double quotes.
 The string is terminated by first next occurrence of quote which started it , so single
quoted strings can include double quotes and vice versa.
 Single quoted strings are treated as it is-
‘Fridayn’
 ‘Friday’--- String
 ‘Fridayn’---String with seven characters including last character which is a new
line.
 n-newline,t-tab,U-uppercase
 There is more than one way to choose your own quote
 1.quote — q
 2.double quote– qq
 q /any string/
 or q(any string) and qq(any string), qq /any string/
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8. VARIABLES AND ASSIGNMENT
 Perl uses – ‘=‘ as the assignment operator. It returns a value. This permits
statement like
 $b=4+($a=3);
 $a=“Burger”;
 $b=“Sandwich $a” //$b would give “Sandwich Burger”
 $c=“turkey $a”;
 Scalar variable names start with--$
 $a=“java”;
 $b=“${a} script”;//value is javascript
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9. <STDIN>
 <STDIN>is used for acquiring input from keyboard.If no input is queued
perl will wait until a line is typed and the return key pressed.
 End-of-file
ctrl - D  Unix
ctrl - Z  DOS
 They cause the return to be undefined, it evaluates to “ “ .
 The empty string is treated as false in boolean context.
while(<STDIN>){
.....
}
To process all statements until the end of file is reached.
While(defined <STDIN>){
...
}
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