PERL INTRODUCTION
Perl is a general-purpose programming language originally developed for text manipulation and now used for a wide range of tasks including system administration, web development, network programming, GUI development, and more. What is Perl? Perl is a stable, cross platform programming language. Though Perl is not officially an acronym but few people used it as Practical Extraction and Report Language. It is used for mission critical projects in the public and private sectors. Perl is an Open Source software, licensed under its Artistic License, or the GNU General Public License (GPL). Perl was created by Larry Wall. Perl 1.0 was released to usenet's alt.comp.sources in 1987 At the time of writing thi tutorial, latest version of perl is 5.16.2 Perl is listed in the Oxford English Dictionary. PC Magazine named Perl a finalist for its 1998 Technical Excellence Award in the Development Tool category. Perl Features Perl takes the best features from other languages, such as C, awk, sed, sh, and BASIC, among others. Perls database integration interface DBI supports third-party databases including Oracle, Sybase, Postgres, MySQL and others. Perl works with HTML, XML, and other mark-up languages. Perl supports Unicode. Perl is Y2K compliant. Perl supports both procedural and object-oriented programming. Perl interfaces with external C/C++ libraries through XS or SWIG. Perl is extensible. There are over 20,000 third party modules available from the Comprehensive Perl Archive Network (CPAN). The Perl interpreter can be embedded into other systems. Perl and the Web Perl used to be the most popular web programming language due to its text manipulation capabilities and rapid development cycle. Perl is widely known as " the duct-tape of the Internet". Perl can handle encrypted Web data, including e-commerce transactions. Perl can be embedded into web servers to speed up processing by as much as 2000%.
Perl's mod_perl allows the Apache web server to embed a Perl interpreter. Perl's DBI package makes web-database integration easy. Perl is Interpreted Perl is an interpreted, which means that your code can be run as is, without a compilation stage that creates a non portable executable program. Traditional compilers convert programs into machine language. When you run a Perl program, it's first compiled into a byte code, which is then converted ( as the program runs) into machine instructions. So it is not quite the same as shells, or Tcl, which are strictly interpreted without an intermediate representation. Neither it is like most versions of C or C++, which are compiled directly into a machine dependent format. It is somewhere in between, along with Python and awk and Emacs .elc files. PERL - ENVIRONMENT SETUP PERL - ENVIRONMENT SETUP Before we start writing our Perl programs, let's understand how to setup our Perl environment. Perl is available on a wide variety of platforms: Unix (Solaris, Linux, FreeBSD, AIX, HP/UX, SunOS, IRIX etc.) Win 9x/NT/2000/ WinCE Macintosh (PPC, 68K) Solaris (x86, SPARC) OpenVMS Alpha (7.2 and later) Symbian Debian GNU/kFreeBSD MirOS BSD And many more... This is more likely that your system will have perl installed on it. Just try giving following command at the $ prompt:
$perl -v
If you have perl installed on your machine then you will get a message something as follows:
This is perl 5, version 16, subversion 2 (v5.16.2) built for i686-linux
Copyright 1987-2012, Larry Wall
Perl may be copied only under the terms of either the Artistic License or the GNU General Public License, which may be found in the Perl 5 source kit.
Complete documentation for Perl, including FAQ lists, should be found on this system using "man perl" or "perldoc perl". If you have access to the Internet, point your browser at http://www.perl.org/, the Perl Home Page.
If you do not have perl already installed then proceed to the next section. Getting Perl Installation
The most up-to-date and current source code, binaries, documentation, news, etc. is available at the official website of Perl: Perl Official Website : http://www.perl.org/ You can download Perl documentation from the following site. Perl Documentation Website : http://perldoc.perl.org Install Perl: Perl distribution is available for a wide variety of platforms. You need to download only the binary code applicable for your platform and install Perl. If the binary code for your platform is not available, you need a C compiler to compile the source code manually. Compiling the source code offers more flexibility in terms of choice of features that you require in your installation. Here is a quick overview of installing Perl on various platforms: Unix & Linux Installation Here are the simple steps to install Perl on Unix/Linux machine. Open a Web browser and go to http://www.perl.org/get.html Follow the link to download zipped source code available for Unix/Linux. Download perl-5.x.y.tar.gz file and issue the following commands at $ prompt.
$tar -xzf perl-5.x.y.tar.gz $cd perl-5.x.y $./Configure -de $make $make test $make install
NOTE: Here $ is Unix prompt where you type your command, so make sure you are not typing $ while typing above mentioned commands. This will install Perl in a standard location /usr/local/bin and its libraries are installed in /usr/local/lib/perlXX where XX is the version of Perl that you are using. It will take a while to compile the source code after issuing make command. Once installation is done, you can issue perl -v command at $ prompt to check perl installation. If everything is fine then it will display message like I have shown above. Windows Installation: Here are the steps to install Perl on Windows machine. Follow the link for the Strawberry Perl installation on Windows http://strawberryperl.com Download either 32bit or 64bit version of installation. Run the downloaded file by double-clicking it in Windows Explorer. This brings up the Perl install wizard, which is really easy to use. Just accept the default settings, wait until the install is finished, and you're ready to roll! Macintosh Installation In order to build your own version of Perl you will need 'make' this is part of the Apples developer tools usually supplied with Mac OS install DVDs. You do not need the latest version of Xcode (which is now charged for) in order to install make. Here are the simple steps to install Perl on Mac OS X machine.
Open a Web browser and go to http://www.perl.org/get.html Follow the link to download zipped source code available for Mac OS X. Download perl-5.x.y.tar.gz file and issue the following commands at $ prompt.
$tar -xzf perl-5.x.y.tar.gz $cd perl-5.x.y $./Configure -de $make $make test $make install
This will install Perl in a standard location /usr/local/bin and its libraries are installed in /usr/local/lib/perlXX where XX is the version of Perl that you are using. Running Perl There are following different ways to start Perl: (1) Interactive Interpreter: You can enter perl and start coding right away in the interactive interpreter by starting it from the command line. You can do this from Unix, DOS, or any other system which provides you a command-line interpreter or shell window.
$perl -e <perl code> # Unix/Linux
or
C:>perl -e <perl code> # Windows/DOS
Here is the list of all the available command line options:
Option Description -d[:debugger] Run program under debugger -Idirectory Specify @INC/#include directory -T Enable tainting checks -t Enable tainting warnings -U Allow unsafe operations -w Enable many useful warnings -W Enable all warnings -X Disable all warnings -e program run Perl script sent in as program file run Perl script from a given file
(2) Script from the Command-line: A Perl script is a text file which keeps perl code in it and it can be executed at command line by invoking the interpreter on your application, as in the following:
$perl script.pl # Unix/Linux
or
C:>perl script.pl # Windows/DOS (3) Integrated Development Environment You can run Perl from a graphical user interface (GUI) environment as well. All you need is a GUI application on your system that supports Perl. You can download Padre, the Perl IDE. You can also use Eclipse Plugin EPIC - Perl Editor and IDE for Eclipse if you are familiar with Eclipse. Before proceeding to next chapter, make sure your environment is properly setup and working perfectly fine. If you are not able to setup the environment properly then you can take help from your system admininstrator. Al the examples given in subsequent chapters have been executed with v5.16.2 version available on CentOS flavor of Linux. PERL - SYNTAX OVERVIEW PERL - SYNTAX OVERVIEW Perl borrows syntax and concepts from many languages: awk, sed, C, Bourne Shell, Smalltalk, Lisp and even English. However, there are some definite differences between the languages. This chapter is designed to quickly get you up to speed on the syntax that is expected in Perl. A Perl program consists of a sequence of declarations and statements which run from the top to the bottom. Loops, subroutines, and other control structures allow you to jump around within the code. Every simple statement must end with a semicolon (;). Perl is a free-form language: you can format and indent it however you like. Whitespace serves mostly to separate tokens, unlike languages like Python where it is an important part of the syntax, or Fortran where it is immaterial. First Perl Program Interactive Mode Programming: You can use Perl interpreter with -e option at command line which lets you execute Perl statements from the command line. Let's try something at $ prompt as follows:
$perl -e 'print "Hello World\n"'
This execution will produce following result:
Hello, world Script Mode Programming Assuming you are already on $ prompt. So let's open a text file hello.pl using vi or vim editor and put the following lines inside your file.
#!/usr/bin/perl
# This will print "Hello, World" print "Hello, world\n";
Here /usr/bin/perl is actual perl interpreter binary. Before you execute your script be sure to change the mode of the script file and give execution priviledge, generally a setting of 0755 works perfectly and finally and finally you execute above script as follows:
$chmod 0755 hello.pl $./hello.pl
This execution will produce following result:
Hello, world
You can use parentheses for functions arguments or omit them according to your personal taste. They are only required occasionally to clarify issues of precedence. Following two statements produce same result.
print("Hello, world\n"); print "Hello, world\n"; Perl File Extension A Perl script can be created inside of any normal simple-text editor program. There are several programs available for every type of platform. There are many programs designed for programmers available for download on the web. As a Perl convention, a Perl file must be saved with a .pl or .PL file extension in order to be recognized as a functioning Perl script. File names can contain numbers, symbols, and letters but must not contain a space. Use an underscore (_) in places of spaces. Comments in Perl Comments in any programming language are friends of developers. Comments can be used to make program user friendly and they are simply skipped by the interpreter without impacting code functionality. For example, in the above program a line starting with hash # is a comment. Simply saying comments in Perl start with a hash symbol and run to the end of the line:
# This is a comment in perl
Lines starting with = are interpreted as the start of a section of embedded documentation (pod), and all subsequent lines until the next =cut are ignored by the compiler. Following is the example:
#!/usr/bin/perl
# This is a single line comment print "Hello, world\n";
=begin comment This is all part of multiline comment. You can use as many lines as you like These comments will be ignored by the compiler until the next =cut is encountered. =cut
This will produce following result:
Hello, world Whitespaces in Perl A Perl program does not care about whitespaces. Following program works perfectly fine:
#!/usr/bin/perl
print "Hello, world\n";
But if spaces are inside the quoted strings then they would be printed as is. For example:
#!/usr/bin/perl
# This would print with a line break in the middle print "Hello world\n";
This will produce following result:
Hello world
All types of whitespace like spaces, tabs, newlines, etc. are equivalent for the interpreter when they are used outside of the quotes. A line containing only whitespace, possibly with a comment, is known as a blank line, and Perl totally ignores it. Single & Double Quotes in Perl You can use double quotes or single quotes around literal strings as follows:
#!/usr/bin/perl
print "Hello, world\n"; print 'Hello, world\n';
This will produce following result:
Hello, world Hello, world\n$
There is important different in single and double quotes. Only double quotes interpolate variables and special characters such as newlines \n where as single quote does not interpolate any variable or special character. Check below example where we are using $a as a variable to store a value and later printing that value:
#!/usr/bin/perl
$a = 10; print "Value of a = $a\n"; print 'Value of a = $a\n';
This will produce following result:
Value of a = 10 Value of a = $a\n$ "Here" Documents You can store or print multiline text with a great comfort. Even you can make use of variables inside "here" document. Below is a simple syntax, check carefully there must be no space between the << and the identifier. An identifier may be either a bare word or some quoted text like we used EOF below. If identifier is quoted, the type of quote you use determines the treatment of the text inside the here docoment, just as in regular quoting. An unquoted identifier works like double quotes.
#!/usr/bin/perl
$a = 10; $var = <<"EOF"; This is the syntax for here document and it will continue until it encounters a EOF in the first line. This is case of double quote so variable value will be interpolated. For example value of a = $a EOF print "$var\n";
$var = <<'EOF'; This is case of single quote so variable value will not be interpolated. For example value of a = $a
EOF print "$var\n";
This will produce following result:
This is the syntax for here document and it will continue until it encounters a EOF in the first line. This is case of double quote so variable value will be interpolated. For example value of a = 10
This is case of single quote so variable value will be interpolated. For example value of a = $a Escaping Characters Perl uses the backslash (\) character to escape any type of character that might interfere with our code. Let's take one example where we want to print double quote and $ sign:
#!/usr/bin/perl
$result = "This is \"number\""; print "$result\n"; print "\$result\n";
This will produce following result:
This is "number" $result Perl Identifiers: A Perl identifier is a name used to identify a variable, function, class, module, or other object. A Perl variable name starts with either $, @ or % followed by zero or more letters, underscores, and digits (0 to 9). Perl does not allow punctuation characters such as @, $, and % within identifiers. Perl is a case sensitive programming language. Thus $Manpower and $manpower are two different identifiers in Perl. PERL - DATA TYPES PERL - DATA TYPES Perl is loosely typed language and there is no need to specify a type for your data while using in your program. The Perl interpreter will choose the type based on the context of the data itself. Perl has three basic data types: scalars, arrays of scalars, and hashes of scalars, also known as associative arrays. Here is little detail about these data types.
S.N. Types and Description 1 Scalar: Scalars are simple variables. They are preceded by a dollar sign ($). A scalar is either a number, a string, or a reference. A reference is actually an address of a variable which we will see in upcoming chapters.
2 Arrays: Arrays are ordered lists of scalars that you access with a numeric index which starts with 0. They are preceded by an "at" sign (@).
3 Hashes:
Hashes are unordered sets of key/value pairs that you access using the keys as subscripts. They are preceded by a percent sign (%).
Numeric Literals Perl stores all the numbers internally as either signed integers or double-precision floating-point values. Numeric literals are specified in any of the following floating-point or integer formats:
Type Value Integer 1234 Negative integer -100 Floating point 2000 Scientific notation 16.12E14 Hexadecimal 0xffff Octal 0577
String Literals Strings are sequences of characters. They are usually alphanumeric values delimited by either single (') or double (") quotes. They work much like UNIX shell quotes where you can use single quoted strings and double quoted strings. Double-quoted string literals allows variable interpolation, and single-quoted strings are not. There are certain characters when they are proceeded by a back slash they will have special meaning and they are used to represent like newline (\n) or tab (\t). You can embed newlines or any of the following Escape sequences directly in your double quoted strings:
Escape sequence Meaning \\ Backslash \' Single quote \" Double quote \a Alert or bell \b Backspace \f Form feed \n Newline \r Carriage return \t Horizontal tab \v Vertical tab \0nn Creates Octal formatted numbers \xnn Creates Hexideciamal formatted numbers
\cX Control characters, x may be any character \u Force next character to uppercase \l Force next character to lowercase \U Force all following characters to uppercase \L Force all following characters to lowercase \Q Backslash all following non-alphanumeric characters \E End \U, \L, or \Q
Example Let's see again how strings behaves with single quotation and double quotation. Here we will use string escapes mentioned in the above table and will make use of scalar variable to assign string values.
#!/usr/bin/perl
# This is case of interpolation. $str = "Welcome to \ntutorialspoint.com!"; print "$str\n";
# This is case of non-interpolation. $str = 'Welcome to \ntutorialspoint.com!'; print "$str\n";
# Only W will become upper case. $str = "\uwelcome to tutorialspoint.com!"; print "$str\n";
# Whole line will become capital. $str = "\UWelcome to tutorialspoint.com!"; print "$str\n";
# A portion of line will become capital. $str = "Welcome to \Ututorialspoint\E.com!"; print "$str\n";
# Backsalash non alpha-numeric including spaces. $str = "\QWelcome to tutorialspoint's family"; print "$str\n";
This will produce following result:
Welcome to tutorialspoint.com! Welcome to \ntutorialspoint.com! Welcome to tutorialspoint.com! WELCOME TO TUTORIALSPOINT.COM! Welcome to TUTORIALSPOINT.com! Welcome\ to\ tutorialspoint\'s\ family PERL - VARIABLES PERL - VARIABLES Variables are nothing but reserved memory locations to store values. This means that when you create a variable you reserve some space in memory. Based on the data type of a variable, the interpreter allocates memory and decides what can be stored in the reserved memory. Therefore, by assigning different data types to variables, you can store integers, decimals, or strings in these variables.
We have learnt that Perl has following three basic data types: Scalars Arrays Hashes Accordingly we are going to use three types of variables in Perl. A scalar variable will precede by a dollar sign ($) and it can store either a number, a string, or a reference. A array variable will precede by sign @ and it will store ordered lists of scalars. Finaly Hash variable will precede by sign % and will be used to store sets of key/value pairs. Perl maintains every variable type in a separate namespace. So you can, without fear of conflict, use the same name for a scalar variable, an array, or a hash. This means that $foo and @foo are two different variables. Creating Variables Perl variables do not have to be explicitly declared to reserve memory space. The declaration happens automatically when you assign a value to a variable. The equal sign (=) is used to assign values to variables.
Keep a note that this is mandatory to declare a varibale before we use it if we use use strict statement in our program.
The operand to the left of the = operator is the name of the variable, and the operand to the right of the = operator is the value stored in the variable. For example:
$age = 25; # An integer assignment $name = "John Paul"; # A string $salary = 1445.50; # A floating point
Here 25, "John Paul" and 1445.50 are the values assigned to $age, $name and $salary variables, respectively. Shortly we will see how we can assign values to arrays and hashes. Scalar Variables A scalar is a single unit of data. That data might be a integer number, floating point, a character, a string, a paragraph, or an entire web page. Simply saying it could be anything, but only a single thing. 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 = $age\n"; print "Name = $name\n"; print "Salary = $salary\n";
This will produce following result:
Age = 25 Name = John Paul Salary = 1445.5 Array Variables An array is a variable that stores an ordered list of scalar values. Array variables are preceded by
an "at" (@) sign. To refer to a single element of an array, you will use the dollar sign ($) with the variable name followed by the index of the element in square brackets.
Perl's mod_perl allows the Apache web server to embed a Perl interpreter. Perl's DBI package makes web-database integration easy. Perl is Interpreted Perl is an interpreted, which means that your code can be run as is, without a compilation stage that creates a non portable executable program. Traditional compilers convert programs into machine language. When you run a Perl program, it's first compiled into a byte code, which is then converted ( as the program runs) into machine instructions. So it is not quite the same as shells, or Tcl, which are strictly interpreted without an intermediate representation. Neither it is like most versions of C or C++, which are compiled directly into a machine dependent format. It is somewhere in between, along with Python and awk and Emacs .elc files. PERL - ENVIRONMENT SETUP PERL - ENVIRONMENT SETUP Before we start writing our Perl programs, let's understand how to setup our Perl environment. Perl is available on a wide variety of platforms: Unix (Solaris, Linux, FreeBSD, AIX, HP/UX, SunOS, IRIX etc.) Win 9x/NT/2000/ WinCE Macintosh (PPC, 68K) Solaris (x86, SPARC) OpenVMS Alpha (7.2 and later) Symbian Debian GNU/kFreeBSD MirOS BSD And many more... This is more likely that your system will have perl installed on it. Just try giving following command at the $ prompt:
$perl -v
If you have perl installed on your machine then you will get a message something as follows:
This is perl 5, version 16, subversion 2 (v5.16.2) built for i686-linux
Copyright 1987-2012, Larry Wall
Perl may be copied only under the terms of either the Artistic License or the GNU General Public License, which may be found in the Perl 5 source kit.
Complete documentation for Perl, including FAQ lists, should be found on this system using "man perl" or "perldoc perl". If you have access to the Internet, point your browser at http://www.perl.org/, the Perl Home Page.
If you do not have perl already installed then proceed to the next section. Getting Perl Installation
The most up-to-date and current source code, binaries, documentation, news, etc. is available at the official website of Perl: Perl Official Website : http://www.perl.org/ You can download Perl documentation from the following site. Perl Documentation Website : http://perldoc.perl.org Install Perl: Perl distribution is available for a wide variety of platforms. You need to download only the binary code applicable for your platform and install Perl. If the binary code for your platform is not available, you need a C compiler to compile the source code manually. Compiling the source code offers more flexibility in terms of choice of features that you require in your installation. Here is a quick overview of installing Perl on various platforms: Unix & Linux Installation Here are the simple steps to install Perl on Unix/Linux machine. Open a Web browser and go to http://www.perl.org/get.html Follow the link to download zipped source code available for Unix/Linux. Download perl-5.x.y.tar.gz file and issue the following commands at $ prompt.
$tar -xzf perl-5.x.y.tar.gz $cd perl-5.x.y $./Configure -de $make $make test $make install
NOTE: Here $ is Unix prompt where you type your command, so make sure you are not typing $ while typing above mentioned commands. This will install Perl in a standard location /usr/local/bin and its libraries are installed in /usr/local/lib/perlXX where XX is the version of Perl that you are using. It will take a while to compile the source code after issuing make command. Once installation is done, you can issue perl -v command at $ prompt to check perl installation. If everything is fine then it will display message like I have shown above. Windows Installation: Here are the steps to install Perl on Windows machine. Follow the link for the Strawberry Perl installation on Windows http://strawberryperl.com Download either 32bit or 64bit version of installation. Run the downloaded file by double-clicking it in Windows Explorer. This brings up the Perl install wizard, which is really easy to use. Just accept the default settings, wait until the install is finished, and you're ready to roll! Macintosh Installation In order to build your own version of Perl you will need 'make' this is part of the Apples developer tools usually supplied with Mac OS install DVDs. You do not need the latest version of Xcode (which is now charged for) in order to install make. Here are the simple steps to install Perl on Mac OS X machine.
Open a Web browser and go to http://www.perl.org/get.html Follow the link to download zipped source code available for Mac OS X. Download perl-5.x.y.tar.gz file and issue the following commands at $ prompt.
$tar -xzf perl-5.x.y.tar.gz $cd perl-5.x.y $./Configure -de $make $make test $make install
This will install Perl in a standard location /usr/local/bin and its libraries are installed in /usr/local/lib/perlXX where XX is the version of Perl that you are using. Running Perl There are following different ways to start Perl: (1) Interactive Interpreter: You can enter perl and start coding right away in the interactive interpreter by starting it from the command line. You can do this from Unix, DOS, or any other system which provides you a command-line interpreter or shell window.
$perl -e <perl code> # Unix/Linux
or
C:>perl -e <perl code> # Windows/DOS
Here is the list of all the available command line options:
Option Description -d[:debugger] Run program under debugger -Idirectory Specify @INC/#include directory -T Enable tainting checks -t Enable tainting warnings -U Allow unsafe operations -w Enable many useful warnings -W Enable all warnings -X Disable all warnings -e program run Perl script sent in as program file run Perl script from a given file
(2) Script from the Command-line: A Perl script is a text file which keeps perl code in it and it can be executed at command line by invoking the interpreter on your application, as in the following:
$perl script.pl # Unix/Linux
or
C:>perl script.pl # Windows/DOS (3) Integrated Development Environment You can run Perl from a graphical user interface (GUI) environment as well. All you need is a GUI application on your system that supports Perl. You can download Padre, the Perl IDE. You can also use Eclipse Plugin EPIC - Perl Editor and IDE for Eclipse if you are familiar with Eclipse. Before proceeding to next chapter, make sure your environment is properly setup and working perfectly fine. If you are not able to setup the environment properly then you can take help from your system admininstrator. Al the examples given in subsequent chapters have been executed with v5.16.2 version available on CentOS flavor of Linux. PERL - SYNTAX OVERVIEW PERL - SYNTAX OVERVIEW Perl borrows syntax and concepts from many languages: awk, sed, C, Bourne Shell, Smalltalk, Lisp and even English. However, there are some definite differences between the languages. This chapter is designed to quickly get you up to speed on the syntax that is expected in Perl. A Perl program consists of a sequence of declarations and statements which run from the top to the bottom. Loops, subroutines, and other control structures allow you to jump around within the code. Every simple statement must end with a semicolon (;). Perl is a free-form language: you can format and indent it however you like. Whitespace serves mostly to separate tokens, unlike languages like Python where it is an important part of the syntax, or Fortran where it is immaterial. First Perl Program Interactive Mode Programming: You can use Perl interpreter with -e option at command line which lets you execute Perl statements from the command line. Let's try something at $ prompt as follows:
$perl -e 'print "Hello World\n"'
This execution will produce following result:
Hello, world Script Mode Programming Assuming you are already on $ prompt. So let's open a text file hello.pl using vi or vim editor and put the following lines inside your file.
#!/usr/bin/perl
# This will print "Hello, World" print "Hello, world\n";
Here /usr/bin/perl is actual perl interpreter binary. Before you execute your script be sure to change the mode of the script file and give execution priviledge, generally a setting of 0755 works perfectly and finally and finally you execute above script as follows:
$chmod 0755 hello.pl $./hello.pl
This execution will produce following result:
Hello, world
You can use parentheses for functions arguments or omit them according to your personal taste. They are only required occasionally to clarify issues of precedence. Following two statements produce same result.
print("Hello, world\n"); print "Hello, world\n"; Perl File Extension A Perl script can be created inside of any normal simple-text editor program. There are several programs available for every type of platform. There are many programs designed for programmers available for download on the web. As a Perl convention, a Perl file must be saved with a .pl or .PL file extension in order to be recognized as a functioning Perl script. File names can contain numbers, symbols, and letters but must not contain a space. Use an underscore (_) in places of spaces. Comments in Perl Comments in any programming language are friends of developers. Comments can be used to make program user friendly and they are simply skipped by the interpreter without impacting code functionality. For example, in the above program a line starting with hash # is a comment. Simply saying comments in Perl start with a hash symbol and run to the end of the line:
# This is a comment in perl
Lines starting with = are interpreted as the start of a section of embedded documentation (pod), and all subsequent lines until the next =cut are ignored by the compiler. Following is the example:
#!/usr/bin/perl
# This is a single line comment print "Hello, world\n";
=begin comment This is all part of multiline comment. You can use as many lines as you like These comments will be ignored by the compiler until the next =cut is encountered. =cut
This will produce following result:
Hello, world Whitespaces in Perl A Perl program does not care about whitespaces. Following program works perfectly fine:
#!/usr/bin/perl
print "Hello, world\n";
But if spaces are inside the quoted strings then they would be printed as is. For example:
#!/usr/bin/perl
# This would print with a line break in the middle print "Hello world\n";
This will produce following result:
Hello world
All types of whitespace like spaces, tabs, newlines, etc. are equivalent for the interpreter when they are used outside of the quotes. A line containing only whitespace, possibly with a comment, is known as a blank line, and Perl totally ignores it. Single & Double Quotes in Perl You can use double quotes or single quotes around literal strings as follows:
#!/usr/bin/perl
print "Hello, world\n"; print 'Hello, world\n';
This will produce following result:
Hello, world Hello, world\n$
There is important different in single and double quotes. Only double quotes interpolate variables and special characters such as newlines \n where as single quote does not interpolate any variable or special character. Check below example where we are using $a as a variable to store a value and later printing that value:
#!/usr/bin/perl
$a = 10; print "Value of a = $a\n"; print 'Value of a = $a\n';
This will produce following result:
Value of a = 10 Value of a = $a\n$ "Here" Documents You can store or print multiline text with a great comfort. Even you can make use of variables inside "here" document. Below is a simple syntax, check carefully there must be no space between the << and the identifier. An identifier may be either a bare word or some quoted text like we used EOF below. If identifier is quoted, the type of quote you use determines the treatment of the text inside the here docoment, just as in regular quoting. An unquoted identifier works like double quotes.
#!/usr/bin/perl
$a = 10; $var = <<"EOF"; This is the syntax for here document and it will continue until it encounters a EOF in the first line. This is case of double quote so variable value will be interpolated. For example value of a = $a EOF print "$var\n";
$var = <<'EOF'; This is case of single quote so variable value will not be interpolated. For example value of a = $a
EOF print "$var\n";
This will produce following result:
This is the syntax for here document and it will continue until it encounters a EOF in the first line. This is case of double quote so variable value will be interpolated. For example value of a = 10
This is case of single quote so variable value will be interpolated. For example value of a = $a Escaping Characters Perl uses the backslash (\) character to escape any type of character that might interfere with our code. Let's take one example where we want to print double quote and $ sign:
#!/usr/bin/perl
$result = "This is \"number\""; print "$result\n"; print "\$result\n";
This will produce following result:
This is "number" $result Perl Identifiers: A Perl identifier is a name used to identify a variable, function, class, module, or other object. A Perl variable name starts with either $, @ or % followed by zero or more letters, underscores, and digits (0 to 9). Perl does not allow punctuation characters such as @, $, and % within identifiers. Perl is a case sensitive programming language. Thus $Manpower and $manpower are two different identifiers in Perl. PERL - DATA TYPES PERL - DATA TYPES Perl is loosely typed language and there is no need to specify a type for your data while using in your program. The Perl interpreter will choose the type based on the context of the data itself. Perl has three basic data types: scalars, arrays of scalars, and hashes of scalars, also known as associative arrays. Here is little detail about these data types.
S.N. Types and Description 1 Scalar: Scalars are simple variables. They are preceded by a dollar sign ($). A scalar is either a number, a string, or a reference. A reference is actually an address of a variable which we will see in upcoming chapters.
2 Arrays: Arrays are ordered lists of scalars that you access with a numeric index which starts with 0. They are preceded by an "at" sign (@).
3 Hashes:
Hashes are unordered sets of key/value pairs that you access using the keys as subscripts. They are preceded by a percent sign (%).
Numeric Literals Perl stores all the numbers internally as either signed integers or double-precision floating-point values. Numeric literals are specified in any of the following floating-point or integer formats:
Type Value Integer 1234 Negative integer -100 Floating point 2000 Scientific notation 16.12E14 Hexadecimal 0xffff Octal 0577
String Literals Strings are sequences of characters. They are usually alphanumeric values delimited by either single (') or double (") quotes. They work much like UNIX shell quotes where you can use single quoted strings and double quoted strings. Double-quoted string literals allows variable interpolation, and single-quoted strings are not. There are certain characters when they are proceeded by a back slash they will have special meaning and they are used to represent like newline (\n) or tab (\t). You can embed newlines or any of the following Escape sequences directly in your double quoted strings:
Escape sequence Meaning \\ Backslash \' Single quote \" Double quote \a Alert or bell \b Backspace \f Form feed \n Newline \r Carriage return \t Horizontal tab \v Vertical tab \0nn Creates Octal formatted numbers \xnn Creates Hexideciamal formatted numbers
\cX Control characters, x may be any character \u Force next character to uppercase \l Force next character to lowercase \U Force all following characters to uppercase \L Force all following characters to lowercase \Q Backslash all following non-alphanumeric characters \E End \U, \L, or \Q
Example Let's see again how strings behaves with single quotation and double quotation. Here we will use string escapes mentioned in the above table and will make use of scalar variable to assign string values.
#!/usr/bin/perl
# This is case of interpolation. $str = "Welcome to \ntutorialspoint.com!"; print "$str\n";
# This is case of non-interpolation. $str = 'Welcome to \ntutorialspoint.com!'; print "$str\n";
# Only W will become upper case. $str = "\uwelcome to tutorialspoint.com!"; print "$str\n";
# Whole line will become capital. $str = "\UWelcome to tutorialspoint.com!"; print "$str\n";
# A portion of line will become capital. $str = "Welcome to \Ututorialspoint\E.com!"; print "$str\n";
# Backsalash non alpha-numeric including spaces. $str = "\QWelcome to tutorialspoint's family"; print "$str\n";
This will produce following result:
Welcome to tutorialspoint.com! Welcome to \ntutorialspoint.com! Welcome to tutorialspoint.com! WELCOME TO TUTORIALSPOINT.COM! Welcome to TUTORIALSPOINT.com! Welcome\ to\ tutorialspoint\'s\ family PERL - VARIABLES PERL - VARIABLES Variables are nothing but reserved memory locations to store values. This means that when you create a variable you reserve some space in memory. Based on the data type of a variable, the interpreter allocates memory and decides what can be stored in the reserved memory. Therefore, by assigning different data types to variables, you can store integers, decimals, or strings in these variables.
We have learnt that Perl has following three basic data types: Scalars Arrays Hashes Accordingly we are going to use three types of variables in Perl. A scalar variable will precede by a dollar sign ($) and it can store either a number, a string, or a reference. A array variable will precede by sign @ and it will store ordered lists of scalars. Finaly Hash variable will precede by sign % and will be used to store sets of key/value pairs. Perl maintains every variable type in a separate namespace. So you can, without fear of conflict, use the same name for a scalar variable, an array, or a hash. This means that $foo and @foo are two different variables. Creating Variables Perl variables do not have to be explicitly declared to reserve memory space. The declaration happens automatically when you assign a value to a variable. The equal sign (=) is used to assign values to variables.
Keep a note that this is mandatory to declare a varibale before we use it if we use use strict statement in our program.
The operand to the left of the = operator is the name of the variable, and the operand to the right of the = operator is the value stored in the variable. For example:
$age = 25; # An integer assignment $name = "John Paul"; # A string $salary = 1445.50; # A floating point
Here 25, "John Paul" and 1445.50 are the values assigned to $age, $name and $salary variables, respectively. Shortly we will see how we can assign values to arrays and hashes. Scalar Variables A scalar is a single unit of data. That data might be a integer number, floating point, a character, a string, a paragraph, or an entire web page. Simply saying it could be anything, but only a single thing. 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 = $age\n"; print "Name = $name\n"; print "Salary = $salary\n";
This will produce following result:
Age = 25 Name = John Paul Salary = 1445.5 Array Variables An array is a variable that stores an ordered list of scalar values. Array variables are preceded by
an "at" (@) sign. To refer to a single element of an array, you will use the dollar sign ($) with the variable name followed by the index of the element in square brackets.
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