Simple Statements and Modifiers

Perl Tutorials - Herong's Tutorial Examples

∟Expressions, Operations and Simple Statements

∟Simple Statements and Modifiers

This section describes simple statements - an expression terminated with semicolon. Simple statements can have modifiers: if, unless, while, until, foreach.

In a Perl script, an expression can be used as a simple statement with these rules:

An expression followed by semicolon (;) becomes a simple statement. For example, $i++; is a simple statement.
Assignments are expressions, not statements. For example, $price=9.99; is a simple statement with a scalar value expression of one assignment operation. $title="Book", $price=9.99; is a simple statement with a list value expression of two assignment operations.
Multiple statements can be written in a single line.
A single statement can be written in multiple lines.

A simple statement can have modifiers at the end of the statement:

EXPR if CONDITION; - EXPR will be evaluated only if CONDITION is evaluated to TRUE.
EXPR unless CONDITION; - EXPR will be evaluated only if CONDITION is evaluated to FALSE.
EXPR while CONDITION; - EXPR will be evaluated multiple times until CONDITION is evaluated to FALSE.
EXPR until CONDITION; - EXPR will be evaluated multiple times until CONDITION is evaluated to TRUE.
EXPR foreach LIST; - EXPR will be evaluated multiple times by iterating all elements in the LIST.

Here is a Perl tutorial script on simple statements with expressions and statement modifiers:

#- ExpressionStatement.pl
#- Copyright (c) HerongYang.com. All Rights Reserved.

   9.99;                               # A scalar value

   "Hello "."Herong";                  # A concatenation operation

   $i--;                               # A decrement operation
   print($i, "\n");

   $price=0.99;                        # An assignment operation
   print($price, "\n");

   $item="Shipping", $price=9.99;      # Two assignment operations
   print($item, $price, "\n");

   @list = ($item="Book", $price=99.99);
   print(@list, "\n");                 # Three assignment operations
   print($item, $price, "\n");

   $author = "Herong" unless ($author);
   print($author, "\n");               # unless modifier

   $price = "Free" if ($author eq "Herong");
   print($price, "\n");                # if modifier

   $i = 0;
   $i++ while ($i < 100);              # while modifier
   print($i, "\n");

   $s = ":";
   $s .= $_.":" foreach (split(//,"Herong"));
   print($s, "\n");                    # foreach modifier

Here is the output of the tutorial script:

-1
0.99
Shipping9.99
Book99.99
Book99.99
Herong
Free
100
:H:e:r:o:n:g:

Table of Contents

About This Book

Perl on Linux Systems

ActivePerl on Windows Systems

Data Types: Values and Variables

►Expressions, Operations and Simple Statements

What Is an Expression?

Expression Evaluation Context

►Simple Statements and Modifiers

User Defined Subroutines

Perl Built-in Debugger

Name Spaces and Perl Module Files

Symbolic (or Soft) References

Hard References - Addresses of Memory Objects

Objects (or References) and Classes (or Packages)

Typeglob and Importing Identifiers from Other Packages

String Built-in Functions and Performance

File Handles and Data Input/Output

Open Files in Binary Mode

Open Directories and Read File Names

File System Functions and Operations

Image and Picture Processing

Using DBM Database Files

Using MySQL Database Server

Socket Communication Over the Internet

XML::Simple Module - XML Parser and Generator

XML Communication Model

SOAP::Lite - SOAP Server-Client Communication Module

Perl Programs as IIS Server CGI Scripts

CGI (Common Gateway Interface)

XML-RPC - Remote Procedure Call with XML and HTTP

RPC::XML - Perl Implementation of XML-RPC

Integrating Perl with Apache Web Server

CGI.pm Module for Building Web Pages

LWP::UserAgent and Web Site Testing

Converting Perl Script to Executable Binary

Managing Perl Engine and Modules on macOS

Archived Tutorials

References

Full Version in PDF/EPUB