Perl Tutorial

Fundamentals

Input and Output

Control Flow

Arrays and Lists

Hash

Scalars

Strings

Object Oriented Programming in Perl

Subroutines

Regular Expressions

File Handling

Context Sensitivity

CGI Programming

Misc

String Operators in Perl

Strings are a fundamental part of Perl, and the language provides several operators to facilitate their manipulation. This tutorial will cover the primary string operators available in Perl.

1. Concatenation Operator: `.`

The . operator concatenates two strings.

my $str1 = "Hello";
my $str2 = "World";
my $combined = $str1 . " " . $str2;  # "Hello World"

2. Repetition Operator: `x`

The x operator repeats a string a specified number of times.

my $repeated = "ha" x 3;  # "hahaha"

3. String Comparison Operators

Perl provides separate operators for numeric and string comparison. For strings:

Equality: eq
Inequality: ne
Less than: lt
Greater than: gt
Less than or equal: le
Greater than or equal: ge

if ($str1 eq $str2) {
    print "Both strings are equal!";
}

4. Quote Operators: `q` and `qq`

q: It's equivalent to single quotes in Perl. It doesn't interpolate variables.
qq: It's equivalent to double quotes. It interpolates variables.

my $name = "Alice";
print q(Hello, $name!);   # Outputs: Hello, $name!
print qq(Hello, $name!);  # Outputs: Hello, Alice!

5. Here Documents: `<<`

Used to define multi-line strings.

my $long_string = <<END;
This is a long string.
It spans multiple lines.
END

END can be any delimiter. The string starts after the <<END and continues until the delimiter (END in this case) is found at the beginning of a line.

6. Backticks:

Backticks execute a command and capture its output as a string.

my $output = `ls -l`;
print $output;

7. String Interpolation

Variables are automatically expanded inside double-quoted strings.

my $fruit = "apple";
print "I have an $fruit.\n";  # I have an apple.

Escape sequences like \n (newline), \t (tab), etc., are also interpolated inside double-quoted strings.

8. Escape Sequences

Used within double-quoted strings and some other delimiters.

\n: newline
\t: tab
\\: backslash
\": double quote

print "Hello\tWorld\n";  # Hello	World (with a tab between Hello and World)

9. Length Operator: `length`

Though technically a function, length is crucial when dealing with strings as it returns the length of a string.

my $length = length("Hello");  # 5

10. String Increment

The ++ operator can also work on strings, incrementing to the next logical string.

my $str = "a";
$str++;  # "b"

my $str2 = "z";
$str2++;  # "aa"

11. Summary

Perl's string operators make it a formidable language for text processing and string manipulations. Understanding how to utilize these operators can help you efficiently tackle text-based tasks in your Perl scripts.

Concatenation operator (.) in Perl:
- Description: Concatenating two strings using the dot (.) operator.
- Code Example:
```
my $greeting = "Hello, ";
my $name = "Perl";

my $message = $greeting . $name;
```
Repetition operator (x) in Perl strings:
- Description: Repeating a string using the repetition operator (x).
- Code Example:
```
my $stars = "*" x 5;  # Repeats '*' five times
```
String interpolation operator in Perl:
- Description: Interpolating variables into double-quoted strings.
- Code Example:
```
my $language = "Perl";

my $message = "I love $language!";
```

Comparison operators for strings in Perl:

Description: Comparing strings using eq, ne, lt, le, gt, ge.

Code Example:

my $str1 = "Perl";
my $str2 = "Python";

if ($str1 eq $str2) {
    print "Strings are equal.\n";
} else {
    print "Strings are not equal.\n";
}

Perl string operators and variables:
- Description: Using string operators with variables.
- Code Example:
```
my $prefix = "Hello";
my $suffix = "Perl";

my $result = $prefix . ", " . $suffix;
```
Logical operators with strings in Perl:
- Description: Combining string comparisons using logical operators (&&, ||).
- Code Example:
```
my $str1 = "Perl";
my $str2 = "Python";

if ($str1 eq "Perl" && $str2 ne "Perl") {
    print "Condition is true.\n";
}
```
String concatenation vs. interpolation in Perl:
- Description: Understanding the difference between concatenation and interpolation.
- Code Example:
```
my $name = "Perl";

# Concatenation
my $message_concat = "Hello, " . $name;

# Interpolation
my $message_interp = "Hello, $name";
```

Overloading string operators in Perl:

Description: Overloading string operators for custom objects (not common).

Code Example (conceptual):

package MyClass;

use overload
  '.'    => \&concatenate,
  'eq'   => \&equals;

sub new {
  my ($class, $value) = @_;
  return bless { value => $value }, $class;
}

sub concatenate {
  my ($self, $other, $swap) = @_;
  return MyClass->new($self->{value} . $other->{value});
}

sub equals {
  my ($self, $other, $swap) = @_;
  return $self->{value} eq $other->{value};
}