Session 5 Operators in PerlRAM N SANGWAN

WWW.RNSANGWAN.COM

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Arithmetic

Perl operators are the same as in C and Java

these are only good for numbers

but beware:$b = "3" + "5";

print $b, "\n"; # prints the number 8

if a string can be interpreted as a number givenarithmetic operators, it will be

what is the value of $b?:$b = "3" + "five" + 6?

Perl semantics can be tricky to completely understand

Operators - Maths

The usual suspects: + - * / %

$total = $subtotal * (1 + $tax / 100.0);

Exponentiation: **

$cube = $value ** 3;

$cuberoot = $value ** (1.0/3);

Bit-level Operations

left-shift: $val = $bits >> 8;

Operators - Assignments

As usual: = += -= *= /= **= =$value *= 5;

$longword

Numeric Operators

Operator Associativity

++ -- none

unary - right

** right

* / % left

binary + - left

++ and have the highest precedence.

Arithmetic in Perl

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$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, that is, 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

Examples

4 % 2 0

5 / 2 2.5 (5 and 2 are coerced from integers toreals).

$total++ * 3

$a ** 2

$b / $ c / 2

Important. The order of evaluation of operands ofoperators is unspecified. This is left for the compiler todecide. Ex: $x++ * $x--

Operators - Boolean

Boolean (against bits in each byte) Usual operators: & |

Exclusive-or: ^

Bitwise Negation: ~

$picture = $backgnd & ~$mask | $image;

Boolean Assignment &= |= ^=

$picture &= $mask;

Operators-Logical (expressions)

&& And operator

| | Or operator

! Not operator

Operators - Short Circuit Operators

expr1 && expr2

expr1 is evaluated.

expr2 is only evaluated if expr1 was true.

expr1 || expr2

expr1 is evaluated.

expr2 is only evaluated if expr1 was false.

Examples

open () || die couldnt open file;

$debug && print users name is $name\n;

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Equality Operators for Strings

Equality/ Inequality : eq and ne

$language = Perl;

if ($language == Perl) ... # Wrong!

if ($language eq Perl) ... #Correct

Use eq / ne rather than == / != for strings

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Relational Operators for Strings

Greater than Numeric : > String : gt

Greater than or equal to Numeric : >= String : ge

Less than Numeric : < String : lt

Less than or equal to Numeric :

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String Functions

Convert to upper case $name = uc($name);

Convert only the first char to upper case $name = ucfirst($name);

Convert to lower case $name = lc($name);

Convert only the first char to lower case $name = lcfirst($name);

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A String Example Program

Convert to upper case $name = uc($name);

Convert only the first char to upper case $name = ucfirst($name);

Convert to lower case $name = lc($name);

Convert only the first char to lower case $name = lcfirst($name);

#!/usr/bin/perl$var1 = larry;$var2 = moe;$var3 = shemp;Output: Larry, MOE, sHEMP

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A String Example Program

#!/usr/local/bin/perl

$var1 = larry;

$var2 = moe;

$var3 = shemp;

print ucfirst($var1); # Prints 'Larry'

print uc($var2); # Prints 'MOE'

print lcfirst(uc($var3)); # Prints 'sHEMP'

String Operators

String Catenation (.) Append two strings together.Happy . Birthday Happy Birthday.

$str . Holidays Happy Holidays.

The operands are not effected by (.)

Repetition operator (x)Beat OU! x 3 Beat OU! Beat OU! Beat OU!

What about?Happy . Birthday! x 2

Happy Birthday! Birthday!

Chop and Chomp

Chop removes the last character in a string.chop(apples) apple

If $a, $b, and $c are a, an, and ant, then chop($a, $b, $c) a an

Chomp removes the ending input record separator(e.g. newline) in a string. If string does not end with an input record separator, then

chomp does nothing to the string and returns 0.

index and rindex

index searches for the starting position of asubstring.

rindex same as index except search is donefrom right to left.

Examples: index(apples, pp) returns 1

rindex(apples, pp) returns 1

index(apples, p) returns 1

rindex(apples, p) returns 2

index(apples, q) returns -1

substr

substr extracts a substring

The way to call it is: substr(string, position, length)

Examples: substr(fruit juice, 0, 3) returns fru

substr(fruit juice, 3, 5) returns it ju

substr(fruit juice, -3, 3) returns ice

join

Like (.) but appends several strings separated by adeliminator.

The way to call it is:

join Expression, List

Example: $month = 09, $day = 01, $year = 05join /, $month, $day, $year 09/01/05.

join /, $month, $day, 2005 ??

Assignments

Simple assignment operators (=)$x = 2;

$average = $sum / $total;

$x = $y = $b = 2;

$result = 17 * ($sum = $x + $y);

chomp($str = $str1. $str1);

Compound assignment operators (=)$sum += $new_value;

$str .= ing;

$result **= 4;

numeric vs. string comparisons

#!/usr/bin/perl

$a = "123";

$b = "1234";

$c = "124";

if ($b > $c) {

print "$b > $c\n";

} else {

print "$b

Quoting special characters

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\| # Vertical bar

\[ # An open square bracket

\) # A closing parenthesis

\* # An asterisk

\^ # A carat symbol

\/ # A slash

\\ # A backslash

Alternatives and parentheses

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jelly|cream # Either jelly or cream

(eg|le)gs # Either eggs or legs

(da)+ # Either da or dada or dadada or...

Another Example

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#!/usr/bin/perl

my @lines = ("Boston is cold.",

"I like the Boston Red Sox.",

"Boston drivers make me see red!" );

foreach my $line (@lines)

{

if ($line =~ /Boston.*red/i )

{

print "$line\n";

}

}

Thankyou

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