Windows run perl script

1. Есть много способов: можете писать руками путь/к/перлу/perl скрипт.pl (точнее, у вас в качестве пути может быть что-нибудь вроде C:\Program Files\Some Perl\bin), можете добавить путь к перлу в переменную окружения %PATH% и запускать скрипты командой perl скрипт.pl, можете настроить ассоциацию перловых исходников с интерпретатором — вариантов масса. А ещё был когда-то cygwin, где перл конечно же был, а ещё в свежих версиях Windows 10 есть линуксовая подсистема, где тоже перл должен быть.

2. #!/usr/bin/perl — так называемый shebang, особый комментарий, где после решётки с восклицательным знаком пишется путь к интерпретатору (это может быть не только перл) и, если надо, дополнительные параметры (например, #!/usr/bin/perl -F' ' -nla). В юниксоподобных системах это имеет значение — при запуске скрипта без указания команды вызова интерпретатора операционная система как раз в shebang и смотрит, чтобы понять, как же выполнить скрипт — бывают скрипты и без расширений. Под Windows shebang скорее всего роли не играет.

3. Чтобы перл больше ругался, используйте

use warnings;
use strict;

Вместо первой из этих строк можете добавить ключ -w при запуске перлового интерпретатора.

4. IDE с поддержкой перла существуют. Лучшее из того, что попадалось мне под Windows — Komodo IDE. Есть упрощённая бесплатная версия — Komodo Edit: это уже не IDE (нет отладчика, юнит-тестов и ещё кучи всякой всячины), а просто навороченный редактор с поддержкой перла.

Perl Background, Features and Running Scripts

Introducing Perl

Perl is a scripting language, which is used every day by many peo­ple, for a wide va­rie­ty of purposes. It is arguably most popular as an al­ter­na­tive to shell scripting, AWK and sed.

How much Perl you can learn in a specific period, depends on two factors: a) your background and ex­pe­ri­en­ce in other languages, and b) how much time and effort you are wil­ling to de­di­cate prac­tic­ing new topics. The core objective should be to obtain as much self-sufficiency as possible in the generic use of Perl for ar­bi­tra­ry ap­pli­ca­tions.

Our focus initially is on the language, terminology, concepts and good coding conventions of Perl, and not spe­ci­fic ap­pli­ca­tion areas, even if that may not sound appealing. Once a firm con­cept­ual foun­da­tion us­ing cor­rect terminology has been established, you should be able to gain ex­pe­rien­ce in a re­la­tive­ly in­de­pen­dent and self-sufficient manner.

Background

The Perl language was created by Larry Wall in 1987. The name “Perl” is not an acronym, al­though one com­mon explanation suggests it means: “Practical Extraction and Reporting Lang­uage”. That is not official. Others suggest: Pathologically Eclectic Rubbish Lister.

Perl runs on many operating systems, most POSIX-like, including WSL (Windows Subsystem for Linux), but also natively on Windows®. The latest version, as of this writing, is 5.30.1 (released 2019). It can be installed from source, if required. For one rea­son or an­oth­er, which does not concern us here, Perl has been steadily losing ground in popularity, if the TIOBE Index is any indication. In that sense, Ruby and Python are its main “competitors”.

Presumably due to many cryptic Perl scripts and snippets, Perl is considered difficult to learn, read and maintain. This is in no way due to any deficiencies in Perl, but entirely due to ir­res­pon­sib­le script­ers show­ing off their mad Perl ‘skillz’. If Perl is to blame, it is most likely a con­se­quen­ce of a design philosophy that affords programmers freedom to achieve goals in a mul­ti­tude of ways and paradigms — probably more so than any other scripting language. The approach we take, emphasises good coding conventions from the start.

Perl on Windows

The recommended version to use on Windows is Strawberry Perl — it works the most like Perl on POSIX systems (Unixes, MacOS, Linux). On the Strawberry Perl releases page, you will even find a ‘portable’ version, which means it does not require installation, and will run from any directory (preferably one where the whole path contains no spaces or other characters that would require escaping). You can also find Perl in Cygwin, and MSYS2. The latter is recommended if you also use other features of MSYS2, like its port of the Arch Linux package manager: pacman to in­stall, up­date and manage packages.

Strawberry Perl includes C/C++ compilers from MinGW-w64, so that Perl packages from CPAN that contain C/C++ components can be compiled, just like on POSIX systems. This distinguishes it from ActivePerl, which uses its own repository and package manager for modules from Active­State, com­pil­ed on your behalf. ActivePerl does not have a portable version, and it must be in­stal­led. If you can live with that, it is a very Windows-friendly Perl environment.

Perl on MacOS & Linux

On MacOS and Linux, you can consider using Perlbrew, which allows you to install any number of Perl versions in your home directory, without affecting the vendor (system) Perl installation. You can use it to switch between ‘active’ Perl versions. It can be configured to support CPAN. In­stal­led modules will only affect the active version, and will also be installed in your home directory, or /usr/local. An even simpler alternative is to download the latest relocatable Perl; it is self-contained and comes with cpanm (CPAN minus) already installed.

Another option to obtain not only Perl, but almost any other free and/or open source package, including GUI applications like MacVim and Dash, and to keep them up to date, is Homebrew — ‘The missing package manager for MacOS’ (their words). We cannot recommend it highly enough for power users. We would not be using MacOS, if not for Homebrew.

Once you have followed the Perlbrew instructions to get it on your system, you can run (for ex­amp­le): ‘perlbrew install perl-5.16.0’ (or whatever version you prefer, but v5.16 is really a mi­ni­mum). Once installed, you can run: ‘perlbrew switch perl-5.16.0’ to enable your new Perl. We shall assume that you either use Perlbrew, or system Perl, as long as it is at least v5.16. Oc­ca­sion­al­ly, we shall mention features available in later versions.

On Unix variants, you are on your own, since it would be too time-consuming to consider various scenarios for all the Unix flavours. Suffice to say, you should have a system Perl at least. If it is old­er than v5.16, you will just be missing out on a few features — the concepts, terminology, and application remain the same.

Some Considerations

A fundamental principle of Perl is that it provides more than one way to accomplish almost any task. One consequence of this is that Perl code can be very difficult to read, unless the authors have been responsible, and used all the commendable features of Perl, rather than the obscure and terse syntax options. The other consequence is the huge number of Perl keywords available.

Perl does not provide any REPL interface (Read-Eval-Print-Loop), unlike some other languages, for example, Python. You can install the Devel::REPL module, or alternatively, the Reply from CPAN. Since both the modules require quite a few extra pre­requisites, you may want to consider whether you really need a Perl REPL. At minimum, running: ‘perl -de '0'’ on the command line will enter the Perl debugger, and you can then perform some interactive computation. Note that on MacOS the debugger line editor does not recognise arrow keys, and the debugger cannot deal with multi-line blocks with any degree of sophistication (the block must be on one line).

Perl scripts or programs can be executed on the command line with: ‘perl ‹script-name›’. So-cal­led Perl one-liners involve one of several switches (options), and some Perl code enclosed in shell quotes, to be executed directly (no script). This is not so easy on Windows, simply because the Command Prompt is unfortunately somewhat archaic (it does not distinguish between single quotes and double quotes, and escaping is not well-defined).

Perl can also be executed inside several graphical environments, typically called ‘in­te­grat­ed de­ve­lop­ment en­vi­ron­ments’ (IDEs). We advise against the use of IDEs when learning Perl, since we feel it is initially more of a burden than any tangible benefit (code-completion is a pro­duc­ti­vi­ty en­hance­ment, especially if you cannot touch type, but does not aid com­pre­hen­sion, nor know­ledge re­ten­tion). Even syntax-highlighting and automatic indentation has dubious pedagogical value; however, we still recommend a good programmer’s editor at minimum. We use Vim, but your de­ci­sion should be based on rational consideration, not the recommendations of others — there is no best editor for everybody.

Your Linux distribution may not have perldoc installed by default, but it is often available as a package (e.g.: you may have to run ‘sudo apt install perl-doc’). We consider perldoc and perltidy essential tools.

Basic Scripts

The following will be used as our ‘baseline’ template for scripts. The version of Perl should be as high as you can manage — this depends on the version of Perl available in your environment, or the re­qui­re­ments for your project.

Modern Perl

Although many tutorials do not discuss it until later, we con­sid­er it almost mandatory, right from the start, that you add ‘use strict;’ to your Perl scripts. Using a specific version (v5.16 as mi­ni­mum) will enable some modern features, and automatically enable strict mode. Otherwise, Perl allows you to write code that, in a mod­ern con­text, is generally viewed as bad practice.

Starter Template

Below is a commented template you can use for any new script. Unnecessary comments (text starting with a hash # character) can ob­vi­ous­ly be removed, except for the very first comment, which is a shebang (hash-bang) line. Do not follow advice from older material to change it to #!/usr/bin/perl.

template.pl — Example Perl Script Template

#!/usr/bin/env perl
#
# @file    template.pl
# @brief   Example Perl Script Template
# @date    2019-12-12
# @licence MIT (https://opensource.org/licenses/MIT)
#
use v5.16;   #<- or: `use 5.016;` — just one preference, either works.
use utf8;    #<- optional, but cannot hurt, so you may as well add it.
binmode STDOUT, ":encoding(utf8)"; #<- set standard input and error
binmode STDERR, ":encoding(utf8)"; #   handles for UTF-8 encoding.

...          #  the ‘body’ of your script. what the script must ‘do’.

exit 0;      #<-specify an exit code (`0` == OK, non-zero == NOT-OK).

=encoding utf-8
=pod

=head1 NAME

scriptname

=head1 DESCRIPTION

Some high-level description of this script. Look at `perldoc perlpod`
for more information on what is required in good documentation.

=cut
__END__

The first few lines of comments should contain some official information. Examples are dates, author(s) and licensing. A use strict; pragma line is only necessary if you are using a Perl version earlier than v5.12. If you do not know how to set your editor for UTF-8 encoding, you may well omit the use utf8; line, but you should probably file this away for future investigation.

Vim Mode Lines

You can optionally add a Vim modelines, which allows a way to set file-specific settings by having a special line in a language-specific comment in your file. Here is an example for Perl:

Example Vim modeline for Perl

# vim: set ft=perl ff=unix fenc=utf-8 et ts=8 sts=4 sw=4 :

The settings are consistent with the default configuration for the recommended perltidy Perl code formatting utility.

Perl Pragmas

The lines starting with ‘use’ are cal­led pragmas. For example, a pragma cal­led ‘constant’ allows us to effectively create symbolic constants. The identifiers created require no sigil, and by con­ven­tion, we create them with all-uppercase letters: ‘use constant MAX_LINES => 20;’

Pragmas effectively load Perl modules. The ‘use’ pragma has several variations, as you might see from its documentation. All variations, except one, require a Module name, making constant a module, but in the context of how we use it, and its effect, it is called a pragma. We shall look at use in more de­tail later.

Exit Codes

The ‘exit 0;’ statement is not necessary, but it is a good convention. If some error occurs earlier, and you cannot continue, you can have: ‘exit 1;’ or some other number instead of 1, to indicate that it is not a “normal” completion. Shell scripts and other programs can check the exit code of a pro­gram, and will consider a 0 exit code as “success”.

The exit code of processes can be determined on the command line (POSIX) by inspecting the $? special environment variable. It will contain the exit code of the last process run. The Windows Command Prompt makes the same information available in the %ERRORLEVEL% environment variable.

In PowerShel, the $? environment variable will contain $true for an exit code of 0, and $false for non-zero exit codes. The exact exit code can be found in the $LASTEXITCODE environment variable.

Basic Script Features

From the above template, you may deduce correctly that a hash character (‘#’) starts a comment. This means Perl will ignore all text starting with the ‘#’, until the end of the line. The first line is also a comment, but is special in POSIX shells — it specifies the interpreter to use for this script, if the script has been marked executable: ‘chmod a+x  ‹scriptname›’. This is called a hash-bang or shebang line. It is ignored on Windows when run­ning inside the Command Prompt, or even in PowerShell, but you should add it anyway.

Everything is ignored in a Perl script after ‘__END__’, which is optional. So you can put anything there, like lines of notes or data, which will be available when you read from the ‘DATA’ filehandle in the main script. You can use ‘__DATA__’ instead in other modules called from the main script, in which case you would read from ‘‹module-name›::DATA’.

Regardless of the presence of the ‘__END__’ line, the ‘=pod’ ⋯ ‘=cut’ section is treated as a special comment, so it could have appeared anywhere. We just prefer to put do­cu­men­ta­tion at that lo­ca­tion, especially in educational code where the focus is on syntax.

Running Perl Scripts

You run Perl scripts either by giving the ‘perl’ program a script file as argument, or setting its mode to executable on POSIX systems, with: ‘chmod a+x’. Any text after the script name, will be treated as arguments to the script (Perl makes arguments available to the script, in the ‘@ARGV’ global array).

In Perl for Windows, you are able to run the ‘pl2bat’ utility to create a ‘.bat’ file from a ‘.pl’ script. Running the batch file will run the embedded script. This is not ideal, since redirection and piping with batch files were not serious considerations for the Command Prompt designers, so only do that if you have no other choice.

There is no equivalent of pl2bat for PowerShell (open-sourced in 2016, running on Linux, MacOS and Windows), which is unfortunate. It is beyond our scope here, but you really should consider using PowerShell instead of Command Prompt on Windows. A PowerShell package does allow you to call PowerShell commands from Perl.

Warnings and Diagnostics

While learning Perl, or even later when looking for program issues or bugs, you can add the -w (useful warnings), or -W (all warnings) switch to the Perl interpreter executable, e.g.: ‘perl -w hello.pl’. More verbose messages can be obtained with: …-Mdiagnostics….

You can gain many useful insights regarding good modern Perl programming practices from the warnings. You gen­e­ral­ly do not want warnings and diagnostics enabled in production scripts, but for learning and development, both are essential. The benefits must not be underestimated.

Advanced — AutoDie

Perl experts suggest also adding use autodie; as part of your preamble pragmas. The autodie module replaces some functions with ones that succeed or die with lexical scope. Prac­ti­cal­ly, when autodie is in effect, this means you can open a file, without checking its return code to see if it was successful — an exception will occur instead within the current scope (normally an eval block). Here is one example from its documentation:

Advanced use of eval and the autodie module

use feature qw(switch);
 
eval {
   use autodie;
   open(my $fh, '<', $some_file);
   my @records = <$fh>;
   # Do things with @records...
   close($fh);
};

given ($@) { # ☆
   when (undef)   { say "No error";                    }
   when ('open')  { say "Error from open";             }
   when (':io')   { say "Non-open, IO error.";         }
   when (':all')  { say "All other autodie errors."    }
   default        { say "Not an autodie error at all." }
}

^☆The given switch was introduced in Perl 5.10, so if you already have ‘use v5.16’ or higher, add­ing ‘use feature qw(switch);’ will be redundant.

As this is a bit advanced, you may ignore autodie for a while, as long as you do not entirely forget about it. You can start using it once you have gained more experience. Using the autodie module without an eval block, still means your script will terminate if a file could not be opened, for example, but that would just be an avoidance technique, not good practice.

Hello World

This represents the simplest professional Perl script — including POD (Plain Old Do­cu­men­ta­tion; see ‘perldoc perlpod’ for more information, in case you are prone to premature curiosity). It does not do much, and exists only to provide a guideline and some structure. You should put all scripts in some working directory, e.g. C:\Course\work, $HOME/Work or in WSL: /mnt/c/Course/Work. The exact name or lo­ca­tion is immaterial, but you should give it some thought.

hello.pl — Annotated Example “Hello World” Perl Script

#!/usr/bin/env perl
#
# @date    2019-12-12
# @author  Incus Data (Pty) Ltd.
# @license MIT https://opensource.org/licenses/MIT
#
use v5.16; use utf8;

print "Hello, World!\n";             #<- embedded newline (escaped).
say "Goodbye, cruel World";          #<- automatic newline added.

exit 0;         #<-good convention. means “successful completion”.

=encoding utf-8
=pod

=head1 NAME

hello.pl

=head1 DESCRIPTION

Example program, printing the traditional "Hello, World!" message,
and showing the difference between `print` and `say`. Comments and
POD are overkill for such a simple program, but are professional.

=cut
__END__

Notice a few points regarding fundamental Perl language features, and some initial terminology:

• Comments start with # (hash characters). Perl ignores text from #, till end of line.
• You should always be aware of which version of Perl you are targeting.
• Statements starting with use, are called pragmas.
• You should use UTF-8 encoding in your editor.
• Perl is case sensitive. Never use names that differ only in their case.
• Perl ignores whitespace (spaces, tabs, newlines). You should use ‘Unix line endings’.
• Perl expects statements to be separated with a semicolon (;); a trailing semicolon is allowed, and treated as a ‘null statement’.
• Text between double quotes ("···"), or single quotes ('···') is called a string literal.
• Special characters, like newline or backslash, must be escaped in a double-quoted string literal.
• Perl is a block-structured language, with blocks delimited by curly-braces. Blocks can appear without a preamble, and provides a lexical scope.
• The __END__ in scripts is optional, and Perl ignores any text following it.

The most fundamental and universally portable way to run a Perl script like hello.pl above is:

perl hello.pl

On POSIX systems, you can do: ‘chmod a+x hello.pl’ to mark it as executable. If it is not on your PATH, you can still execute it as:

./hello.pl

The best you can do on Windows (but it is hardly ideal), is to run the Windows-specific pl2bat program, which will “wrap” the script in a batch file. Thus:

pl2bat hello.pl

will result in hello.bat, which you can run as hello. Redirection and piping do not work well with batch files on Windows, so only use this feature if you never expect to use piping or in­di­rec­tion with the program. Arguments passed to the batch file, will be forwarded to the Perl script.

Running ‘perldoc hello.pl’ will display POD documentation, if present. Here is the output:

NAME
    hello.pl

DESCRIPTION
    Example program, printing the traditional "Hello, World!" message, and
    showing the difference between `print` and `say`. Comments and POD are
    overkill for such a simple program, but are professional.

On Linux and MacOS, we suggest you keep your scripts in a ‘source directory’ with scripts having the .pl extension, and create symbolic links without the extension, in some directory in your $PATH.

Formatting and Indentation

Blank lines should be used to separate logical units of code from one another, much like spaces be­tween paragraphs in many technical books. Blocks should be indented with a consistent number of spaces — called an indentation level. Nested blocks should be indented one level from the outer block.

The location of braces is a style, and should be consistent. We suggest that the open­ing brace appear on the same line as the statement it “belongs” to. The closing curly brace may or may not be indented, but should appear on a line all by itself.

The Perltidy script should not be ignored. It can be installed with ‘cpan Perl::Tidy’, manually downloaded and installed, or it may be available as a package in your Linux distribution. Perltidy can reformat your code according to standard conventions, but has many options to fine-tune its output to your specifications. The best option is to ex­pe­ri­ment with it, and incorporate perltidy in your workflow — especially if you share your work amongst colleagues.

Grouping code in ‘bare blocks’, i.e., curly-brace delimited blocks that are not associated with any statement, is perfectly valid, and a good convention to group related code. One advantage is that variables defined in such a block, are local to the block and will thus not be visible outside the block. This feature of Perl (and C, C#, C++, Java, PHP, JavaScript, etc.) is not used often enough.

Documentation

The documentation on PerlDoc is extensive — it covers the language syntax, built-in func­tions, built-in variables, reg­ul­ar expressions and documentation for the core modules. You can view a list of core mo­dul­es using the ‘corelist’ utility. For example, to list all the standard core modules supplied with Perl v5.16.0, you can run this command:

corelist -v v5.16.0

You should probably pipe the output to ‘less’, or ‘more’, or redirect to a file — the list is big.

For the perl executable, you can run perl --help for a list of available options (switches).

PerlDoc

The ‘perldoc’ program, which is supplied with Perl, can display all the documentation found on Perl­Doc on the command line (in text format, of course, not HTML). It can also dis­play do­cu­men­ta­tion for your scripts, if you documented them according to the perlpod specification. So, for our ex­am­ple script above, you can run the following command (output is shown afterwards):

perldoc template.pl

  NAME
      scriptname

  DESCRIPTION
      Some high-level description of this script. Look at `perldoc perlpod`
      for more information on what is required in good documentation.

‘perldoc’ pipes its output to ‘less’ or ‘more’, but you can redirect it yourself.

To get a table of contents for all the documentation, run:

perltoc perltoc

It will list all the names you can use with ‘perldoc’ to obtain further information. For example, you will read that perlfunc will provide documentation for all Perl’s functions, so you can run:

perldoc perlfunc

For help on a specific function, add the ‘-f’ flag. For example, for documentation specific to the ‘chomp’ function, run:

perldoc -f chomp

For module documentation, including non-core modules you installed additionally, you must specify the full module name (it is case-sensitive):

perldoc Data::Dumper

^☆ ‘Data::Dumper’ is one of the core modules, and is not significant here; it is only used as an ex­am­ple module name.

You can also use: ‘perldoc -q "‹query›"’ to search the Perl FAQ. Unfortunately, it is not a gen­e­ra­lis­ed query; you still need to know the FAQ keywords, which is kind of useless for newcomers.

If HTML appeals to you, the Perl-supplied pod2html converter can convert any POD doc­u­men­ta­tion (including all Perl’s official documentation) to HTML. For example, you can try the following command line:

perldoc -u pod2html > pod2html.html

This will format the pod2html documentation as HTML, which we redirect to the pod2html.html file. You can open this file in your browser. It does not have CSS styling, so it may look a bit bor­ing. You can open the HTML file from the Windows command line with: start pod2html.html, or on MacOS with: open pod2html.html. On Linux, which com­mand you can use depends on your window manager, but try: firefox pod2html.html from your GUI terminal.

Offline Perl Documentation

You can also download the PerlDoc documentation in HTML format, with an embedded Java­Script search engine. Alternatively, you can install Zeal (or use the portable version), and down­load the Perl “docset” for an offline documentation viewer. Zeal can be used to view many other “doc­sets” as well, making it a useful developer tool. On MacOS, use Dash, on which Zeal is based, and whose docsets Zeal uses.

Regarding Zeal:

• Remember you can turn off the ads it displays on the starting page, in the preferences.
• Be patient when updating or downloading docsets, and do not interrupt it.
• Delete the zeal.ini file in the Port­ab­le Zeal directory when moving or renaming it, otherwise it will not work afterwards.

Practical Patterns

When you get started with Perl scripting, you may be impatient to get ‘something useful’ accomplished. We understand that, and encourage you to be patient — the better you learn Perl for the sake of learning Perl, the easier it will be for you to accomplish your goals. With that in mind, we present a number of practical patterns to get you started.

Scalar Variables and Values

The simplest type or category of variables, is the scalar variable, indicated with the $ sigil. Vari­ab­les should be defined before they are used, with the my keyword; it can define several variables at the same time, as long as they are enclosed in parentheses.

Variable definition syntax variations

my $var;                         #<- define single variable.
my ($a, $b, $c);                 #<- define multiple variables.
my $rav = 123;                   #<- define & initialise one variable.
my ($d, $e, $f) = (12, 34, 56);  #<- define & initialise many variables.
my ($g) = (11, 22, 33);          #<- define 1 variable, set it to `11`.
my $h = (11, 22, 33);            #<- define 1 variable, set it to `3`,
                                 #   (number of elements in the list).

List assignment makes it possible to initialise several variables, as the third last statement illustrates. The last two statements illustrate the difference between using, or omitting, the parentheses around a single variable definition. Arrays or lists used in a scalar context, results in the number of elements in the list or array variable.

Variables can store any Perl type, at any time. Basic types are numbers and strings in the form of literals: 123 (integer literal), 1.23 (floating point literal), "ABC" (string literal), 'ABC' (another string literal). Types are converted implicitly as needed, depending on the operation performed on them.

Typical operations include the arithmetic operators, ** for exponentiation or ‘to the power’, % for modulus or ‘remainder’, . for string concatenation. Numbers are compared with: == (equal), != (not equal), < (less than), <= (less than or equal), > (greater than), >= (greater than or equal), and <=> (compare).

String comparisons use different operators: eq, ne, gt, ge, lt, le and cmp. Implicit string operations include string interpolation of variables inside double-quoted string literals.

The ‘compare’ opeators return one of three possible values:

• a negative value if the first operand is smaller than the second;
• a positive value if the first operand is greater than the second;
• or 0 if the operands are equal to each other.

Logical operators && (AND), || (OR) and ! (NOT) are available, as are the word versions: and, or and not (albeit with lower, if not better, precedence). The logical operators exhibits ‘short-circuiting’ behaviour, which means they only evaluate the second (right hand) operand, if the logical result cannot be obtained from the first.

Standard Input and Output

If any program can read from standard input, you can pipe the output of another program to it. In Perl, standard input is represented by the global STDIN file handle variable. As shown in their doc­u­men­ta­tion, many functions expect a ‘FILEHANDLE’ as argument. This means STDIN can be used, although most will use STDIN (or STDOUT) as defaults if not supplied.

Reading from Standard Input

The built-in readline function can read one line of text from a file handle, with STDIN being the de­fault. It returns a scalar string, with a trailing newline ("\n"), which is generally not very useful, so it is common to remove it with the chomp function, leading to some common patterns:

Reading and trimming a line from standard input

my $input = readline;          #<-buffered, one-line input.
chomp($input);                 #<-remove trailing newline if present.

The last two statements can be combined, if the $input variable does not yet exist:

Define variable, read input and trim result pattern

chomp(my $input = readline);   #<-define variable, read input, chomp.

If the user only pressed Enter without typing other text, and you have ‘chomped’ the result, it will be an empty string. If an error or end of file was encountered, the result will be undef (a special Perl value). You can test for these conditions as follows:

Testing for empty input, or end-of-file situations

use v5.16; use utf8;
chomp(my $input = readline);           #<- `chomp` removes trailing newline. 
if (!defined $input) {                 #<- test for EOF or error, and
   say "EOF or error";                 #   must be done first.
   }
elsif ($input eq "") {                 #<- test for blank line; it will
   say "Empty line!";                  #   also be ‘true’ for `undef`.
   }
else {                                 #<- non-zero length input.
   say "Thank you. Input = ", $input;
   }

To simplistically test for numeric input, you can implicitly convert the string to a number by mul­ti­ply­ing it with 1.0. If it fails, which we can trap with eval, the input was not in a format that Perl can convert to a number.

Simple numeric validation

use v5.16; use utf8;
chomp(my $radius = readline);
if (!eval {1.0 * $radius}) {
   say "We have a number: ", $radius;
   }

Testing for numeric input is independent of checks for errors or empty lines; you may have to do those first, depending on your program’s requirements.

Lines can be read until end of file, using several patterns, but we shall show only one here:

Read lines until end of file pattern

use v5.16; use utf8;
while (defined (my $line = readline)) {
   chomp $line;          #<- optional
   say uc $line;         #<- do what you will with `$line`.
   }

You can now pipe the output of a program to the script, or redirect standard input from a file. Assuming the above code was saved in uccat.pl, you can try the following:

Providing files as standard input

We are not exactly sure why all Perl tutorials and examples are so enamoured with using the <STDIN> synonym for readline — presumably because it is tradition, and distinguishes Perl from the more ‘boring’ languages. Since you will see it everywhere, we would be remiss if we did not alert you to it. Most Perl programmers will write the relevant line in our last example in this way:

Classic alternative to readline

while (defined (my $line = <STDIN>)) { ⋯

You are absolutely welcome to use either; at least just be consistent. After all, Perl is a language with many options to per­form the same task — the philosophy of leaving the choice up to the programmer, who knows best; right?

Writing to Standard Output

You have several options in Perl to write output to file handles. There are two standard output handles you should be aware of: STDOUT and STDERR, although the latter is referred to as the stan­dard er­ror handle. This stream you can redirect on the command line with: …2>…, or combine them with: …2>&1… for further redirection or piping.

Functions like say or print by default write to STDOUT. Error messages should be written to STDERR as a matter of good coding practice. Here are some examples:

Writing to standard output and standard error handles

use v5.16; use utf8;
print STDOUT "Hello";               #<- write to `STDOUT` handle.
print ", world!\n";                 #<- default is `STDOUT`.
print 123, " ABC", " DEF";          #<- arbitrary list of arguments.
print STDERR "Error!";              #<- error messages to `STDERR`.
die "Error!. Terminating."          #<- message to `STDERR` & exit.

Please notice that when a file handle is supplied, it must not be followed by a comma. The say function is equivalent to print in every way, except it automatically appends a newline after all arguments have been printed (and is only enabled with a use v5.10; or higher). Neither will put separators between the listed arguments.

The die function not only writes to STDERR, but also terminates the script with a non-zero exit code.

Final Example Script

With some of the basic Perl features, conventions, and patterns in place, we can now write a relatively robust example script that will prompt the user for a radius, which it will validate, and then use to calculate the area and circumference of a circle with that radius:

circle.pl — Simple Example Circle Calculator

#!/usr/bin/env perl
#
# @file    circle.pl
# @brief   Simple Example Circle Calculator
# @date    2019-12-12
# @author  Incus Data (Pty) Ltd.
# @licence MIT (https://opensource.org/licenses/MIT)
#
use v5.16; use utf8;
binmode STDOUT, ":encoding(utf8)"; #<- set UTF-8 encoding for `STDOUT`.
binmode STDERR, ":encoding(utf8)"; #<- set UTF-8 encoding for `STDERR`.

use Math::Trig; #<-for `pi`

print "Radius (positive float)?: ";
my $radius = readline;

# Validation. Terminate if garbage, or negative.
   {
   if (!defined $radius) {
      die "No input.";
      }
   if ($radius eq "\n") {
      die "Empty input.";
      }
   if (!eval { $radius = 1.0 * $radius }) {
      die "Not a number.";
      }
   if ($radius < 0.0) {
      die "Negative radius.";
      }
   }

# Calculate area and circumference, then output.

my $circum = 2.0 * pi * $radius;
my $area = pi * $radius ** 2;

say "Radius  = $radius";
say "Circum. = $circum";
say "Area    = $area";

exit 0;

=encoding utf-8
=pod

=head1 NAME

circle.pl

=head1 DESCRIPTION

Example program, calculating the area and circumference of a circle.
The radius is provided by the user and validated. The program will
terminate on invalid input, with an informational message. It does
not (yet) respond to command-line arguments passed to the script.

=cut

Much can be improved in the program, which we will deal with later; for example, it does not pro­cess command-line arguments, and the output values are not formatted to a certain number of de­ci­mal places. However, this should allow you to start your Perl journey with a good foundation. You can run it through perltidy, should the formatting impact on your sensibilities.

Portability

A final note on writing portable Perl scripts. As far as is reasonable, you should ensure that your scripts run on all supporting platforms. This is not too difficult as documented, but you can also read it with: ‘perldoc perlport’.

One important point to highlight, is that the ‘$^O’ special variable contains the operating system name. On Linux, this will contain: linux; on MacOS: darwin and on Windows: MSWin32 (regardless of whether you are running 32-bit, or 64-bit, Windows). You can use this information to con­di­tion­al­ly load modules, or perform different tasks. There is also the core Config module that will give you the same (and more) information.

Here is an example showing how to portably enable and use VT100/ANSI es­cape se­quen­ces in POSIX shells, the Windows 10 Console, or the newer Windows Terminal (Preview), as well as UTF-8 output.

vtutf8.pl — VT100/ANSI Escape Sequences and UTF-8 Output

#!/usr/bin/env perl
#
# @file    vtutf8.pl
# @brief   VT100/ANSI Escape Sequences and UTF-8
# @date    2019-12-18
# @author  Incus Data (Pty) Ltd.
# @licence MIT (https://opensource.org/licenses/MIT)
#
use v5.16;                            #<-minimum version.
use utf8;                             #<-*source* in UTF-8.
use open ':std', ':encoding(UTF-8)';  #<-all std. I/O in UTF-8.

#= Windows-specific code. Will be ignored on other systems. This may
#  become less necessary with newer vesions of the Windows 10 console,
#  and will not be necessary when running scripts in PowerShell, and/or
#  inside the newer Windows Terminal.
#
if ($^O eq 'MSWin32') {
   use if $^O eq 'MSWin32', 'Win32::Console';
   Win32::Console::OutputCP(65001);
   system(''); #<-enable vt escape sequences processing.
   }

#= At this point, most VT100/ANSI escapes sequences will work portably.
#  Optionally, one may use the core `Term::ANSIColor` module. Do *not*
#  use `Win32::Console::ANSI`.

print "\e[2J\e[0;0H"; #<-clear screen; move cursor.

print "\n  \e[36;7m STANDARD COLOURS \e[0m\n";
print " \x{250C}\x{2500}", "\x{2500}" x 17;
print "\x{2510}\n \x{2502} ";
for (my $color = 0; $color < 8; $color++) {
   print "\e[48;5;${color}m  ";
   }
print "\e[0m \x{2502}\n \x{2502} ";
for (my $color = 8; $color < 16; $color++) {
   print "\x1b[48;5;${color}m  ";
   }
print "\e[0m \x{2502}\n \x{2514}","\x{2500}" x 18,"\x{2518}\n";
print "\e[32m  UTF8: \e[33;1m‹«π®©·§○●»›★\e[0m\n\n";

exit 0;

=encoding utf-8
=pod

=head1 NAME

vtutf8.pl - Portable VT100/ANSI Demonstration

=head1 DESCRIPTION

Portably enables VT100/ANSI terminal escape sequences in a Windows 10
Console. This is disabled by default for console applications. Running
a sub shell with C<system('')>, enables it from that point, but is not
very efficient. Alternatively, one may directly use the Windows API.

This example does not use C<Term::ANSIColors>, but you could. Never use
C<Win32::Console::ANSI> on modern, updated, Windows 10 consoles. Your
font (even POSIX terminals) must support the UTF-8 glyphs you output.

The C<use utf8;> only tells Perl about your source code encoding. To
enable it for I/O, C<use open ':std', ':encoding(UTF-8)'> is also needed.
This arrangement is modern, and now supported by Windows 10 Console
APIs; but it will take a while before Perl, Python, and other command
line shells and programs will enable it by default.

TIP: To clear the screen portably, use the: C<\e2J\e[0;0H> sequence.
=cut

__END__

As the POD mentions, ‘use utf8;’ only tells Perl that your source code is UTF-8 encoded. To en­able UTF-8 on output and also input, and to avoid “Wide character…” warnings, the file handles must be open­ed with :encoding(UTF-8). This is most easily accomplished with the ‘use open std…’ pragma, which will set the default encoding for the standard file handles.

Write and Run Your First Script. All you need to write Perl programs is a text editor. Write Your Script. Create a new text file and type the following exactly as shown: #!usr/bin/perl. Run Your Script. Back at the command prompt, change to the directory where you saved the Perl script.

From Perl HowTo, the most common ways to execute external commands from Perl are: my $files = `ls -la` — captures the output of the command in $files. system “touch ~/foo” — if you don’t want to capture the command’s output. exec “vim ~/foo” — if you don’t want to return to the script after executing the command.

How do I run a .pl file?

Programmers typically open and modify PL files with source code editors, such as Microsoft Visual Studio Code and MacroMates TextMate. Plain text editors, which include Microsoft Notepad and Apple TextEdit, may also be used to open and modify PL files.

Does Windows 10 have Perl?

Windows. Windows does not have Perl installed by default.

Where is Perl path in Windows?

If you’re not sure where you installed Perl to (and can’t find it in the default C:\perl\bin ), you can find the directory by going to Start menu, finding ActiveState Perl folder, and right-clicking on “Perl Package Manager” icon, then pick “Properties” from the right-click menu.

How do I print a Perl script?

print() operator – Print operator prints whatever is passed to it as an argument whether it be a string, a number, a variable or anything. Double-quotes(“”) is used as a delimiter to this operator. Above example, prints both the strings with the help of print function but both the strings are printed in the same line.

How do I read a text file in Perl?

Perl Read File First, we used the open() function to open a file for reading. Second, the syntax while() is equivalent to while(defined($_ = ) . We read a line from a file and assigned it to the special variable $_ . Third, we displayed each line of the file by passing the variable $_ to the print function.

How do I run a PL script in Windows?

Write and Run Your First Script. All you need to write Perl programs is a text editor. Write Your Script. Create a new text file and type the following exactly as shown: #!usr/bin/perl. Run Your Script. Back at the command prompt, change to the directory where you saved the Perl script.

How do I open a PL file in Windows 10?

3 Answers Go into Windows Explorer. Find a file that ends in a *. pl suffix. Right click on it and bring up the Context menu. Select “Open With” (It might just be Open with an ellipse after it. On the bottom of the dialog box is a checkbox (Something like open all extensions with this program).

What is the extension of Perl script?

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.

Which perl is best for Windows?

Padre, the Perl IDE is recommended, because you get Strawberry Perl (Perl packaged for Windows) 5.12. 3 as well as many useful modules (especially those that are tricky to install) and the Perl IDE/editor itself. To interact with the command line and run Perl commands, you need to run ‘cmd’.

How do I install ActiveState perl on Windows?

You can install ActivePerl by downloading and running the Setup Wizard (.exe).Running the ActivePerl Setup Wizard¶ Download and save the installation package. Right-click the .exe file and select Run As Administrator. Follow the prompts on screen to complete the installation.

Which is better Python or perl?

Perl is a high-level programming language that’s easier to learn when compared with Python. Python is more robust, scalable, and stable when compared to Perl. While Perl code can be messy, featuring many paths to accomplish the same goal, Python is clean and streamlined.

How do I find my Perl?

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. You can also type above command under Windows / Mac OS X by opening terminal.

How do I create a Perl path in Windows?

Under System variables, select the Path variable and click Edit to display the Edit environment variable dialog. Click Edit. Add the path to the Perl executable (such as C:\Program Files (x86)\XyEnterprise\Contenta\SPerl\Perl\bin) to the beginning of the value.

Which is better Strawberry Perl vs ActivePerl?

Both are great and work the same. Strawberry Perl is known for being able to build XS modules, but you can do that with ActivePerl too if you just install the Visual Studio SDK (or the free Express version).

How do I print an environment variable in Perl script?

Printing all of your environment variables in Perl In Listing 1, the key (or subscript) was ‘ LOGNAME ‘, and the value of the array element $ENV{‘LOGNAME’} was fred : $ENV{‘LOGNAME’} = “fred”; A listing of a few of the keys of the special associative array %ENV are shown in Listing 2.

How do I print an array in Perl script?

use 5.012_002; use strict; use warnings; my @array = qw/ 1 2 3 4 5 /; { local $” = ‘, ‘; print “@array\n”; # Interpolation. }Apr 21, 2011.

How do I debug a Perl script?

Perl Debugger Tutorial: 10 Easy Steps to Debug Perl Program Enter Perl Debugger. View specific lines or subroutine statements using (l) Set the breakpoint on get_pattern function using (b) Set the breakpoint on specific line using (b) View the breakpoints using (L) step by step execution using (s and n).

Perl, a high-level programming language created by Larry Wall in 1987, has long been a favorite among developers for its versatility and power. Over the years, it has evolved significantly, with a rich ecosystem of modules and libraries that enhance its functionality, making it a valuable tool in the programmer’s toolkit. It’s no wonder so many people want to know how to run Perl scripts.

In this guide, we’ll walk you through the essential steps to run a Perl script effectively. Whether you’re looking to automate a mundane task, analyze data, or dive deeper into programming, understanding how to execute Perl scripts will be a valuable skill in your repertoire.

Setting Up Your Environment

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One of the first questions you might be asking is, “How do I run a Perl program?” Before diving into the answer, it’s essential to set up your environment correctly.

The first step is installing Perl on your machine, which varies slightly depending on your operating system.

Installing Perl

The process you use for installing Perl depends on your device:

• Windows: The easiest way to install Perl on Windows is through the Strawberry Perl distribution, which includes everything you need. Simply download it from Strawberry Perl’s website and follow the installation prompts. For a more robust installation, consider using ActivePerl from ActiveState.
• macOS: Perl comes pre-installed on macOS. To check your version, open Terminal, and type perl -v. If you need the latest version, consider using a package manager like Homebrew. Install Homebrew and then run Brew install Perl to get the latest version.
• Linux: Most Linux distributions come with Perl pre-installed. You can check by typing perl -v in your terminal. If you need to install or upgrade, use your package manager (e.g., sudo apt-get install perl for Ubuntu).

For detailed instructions and troubleshooting, refer to the official Perl documentation.

Choosing a Text Editor

Once Perl is installed, the next step is to select a text editor for writing your scripts. Popular choices include:

• Visual Studio Code: A versatile editor with extensive extensions for Perl.
• Sublime Text: Known for its speed and simplicity, with great syntax highlighting for Perl.
• Atom: A hackable text editor that allows for significant customization.

For a more integrated experience, consider using an IDE like Padre, a Perl IDE explicitly designed for Perl development, or Komodo IDE, which supports multiple languages, including Perl.

With your environment set up, you’re ready to write and run Perl script!

Writing Your First Perl Script

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Now that your environment is set up, it’s time to learn how to execute a Perl program! Perl’s syntax is designed to be straightforward, making it accessible for newcomers while still powerful enough for seasoned developers. Let’s explore the basic structure of a Perl script and walk through an example.

Basic Structure of a Perl Script

A typical Perl script consists of the following components:

• Shebang Line: This is the first line of the script, which tells the system where to find the Perl interpreter. It usually looks like this: #!/usr/bin/perl. This line is essential for running the script directly from the command line.
• Comments: Comments in Perl start with the # symbol and continue to the end of the line. They are used to annotate your code and improve readability without affecting the script’s execution.
• Code Blocks: Perl scripts consist of statements that perform various tasks. These can include variable declarations, control structures (like loops and conditionals), and function definitions.

Example Script: “Hello, World!”

Below, you’ll learn how to execute a Perl script that prints “Hello, World!” to the screen. Here’s the complete code:

#!/usr/bin/perl

# This is a simple Perl script to print "Hello, World!"

use strict;      # Enables strict mode

use warnings;    # Enables warnings

print "Hello, World!\n";  # Print statement with newline

Explanation of Each Line of Code

Here’s a quick breakdown of each line:

Shebang Line
#!/usr/bin/perl

This line specifies the path to the Perl interpreter. When you run the script from the command line, the operating system uses this line to determine which interpreter to execute. If you have installed Perl in a different location, you may need to adjust this path accordingly.

Comment
# This is a simple Perl script to print “Hello, World!”

This comment explains the purpose of the script. Comments are invaluable for others (and your future self) to understand your code’s intent.

Use Statements
use strict;

use warnings;

These statements enable strict mode and warnings in your script. Strict mode enforces good programming practices by requiring you to declare variables before using them, helping prevent common mistakes. Warnings provide helpful alerts about potential issues in your code, making debugging easier.

Print Statement
print “Hello, World!\n”;

This line is where the action happens! The print function outputs text to the screen. The string “Hello, World!\n” is the message we want to display. The \n at the end is a special character representing a new line, ensuring that the cursor moves to the next line after printing.

Running the Script

To run this script, follow these steps:

• Open your preferred text editor and copy the code above into a new file. Save the file with a .pl extension, for example, hello_world.pl.
• Open your terminal or command prompt.
• Navigate to the directory where you saved the script.

Make the script executable (on Unix-based systems) by running:

chmod +x hello_world.pl

Finally, execute the script by typing:

./hello_world.pl

You should see the output: Hello, World! Congratulations! You’ve just written and executed your first Perl script. This simple exercise sets the foundation for more complex scripting and programming tasks. As you continue to explore Perl, you’ll discover its rich features and powerful capabilities.

Running Perl Scripts

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Once you’ve written your Perl script, the next step is executing it. There are various methods to run Perl scripts, with the command line and Integrated Development Environments (IDEs) being the most common. In this section, we’ll explore both methods, along with troubleshooting tips for common issues.

Using the Command Line

Executing a Perl script from the command line is straightforward. Here’s a step-by-step guide:

Open the Terminal or Command Prompt

• On Windows, search for “Command Prompt” or “PowerShell.”
• On macOS, use “Terminal,” found in Applications > Utilities.
• On Linux, open your preferred terminal emulator.

Navigate to Your Script’s Directory

Use the cd command (change directory) to navigate to the folder containing your Perl script. For example:

cd path/to/your/script

Run the Perl Script

To execute your script, type the following command:

perl your_script.pl

Replace your_script.pl with the name of your actual script. If you’ve included the shebang line (#!/usr/bin/perl), you can also make the script executable and run it directly:

chmod +x your_script.pl

./your_script.pl

Common Command-Line Flags and Options:

• -w: Enables warnings for potential issues in your code.
• -c: Checks the syntax of the script without executing it.
• -d: Runs the script in debugging mode, allowing you to step through the code.

Using an IDE

Many developers prefer using an IDE for writing and running Perl scripts due to its integrated features. Here’s how to run Perl scripts in some popular IDEs:

Visual Studio Code (VS Code)

• Install the Perl extension from the marketplace.
• Open your Perl script and run it by right-clicking in the editor and selecting “Run Perl Script” or by using the integrated terminal.

Padre

• Open your script within Padre.
• Click on the “Run” button or use the shortcut (usually F5) to execute the script. The output will appear in the output pane.

Komodo IDE

• Open your script and click on the “Run” button on the toolbar.
• You can configure run configurations for different Perl environments if needed.

Troubleshooting Common Errors

Errors are a natural part of programming, and understanding common Perl error messages can significantly improve your debugging skills.

Common Error Messages

• “Can’t locate module…”: This means Perl cannot find the specified module. Ensure the module is installed and the @INC paths are correctly set.
• “Syntax error at line X”: Indicates an issue with the syntax at the specified line. Check for missing semicolons, mismatched parentheses, or unclosed quotes.
• “Use of uninitialized value…”: This warning suggests you’re trying to use a variable that hasn’t been defined yet. Ensure all variables are initialized before use.

Tips for Debugging Perl Scripts

• Use Warnings and Strict Mode: Always include use warnings; and use strict; at the top of your scripts. These help catch common mistakes and enforce good coding practices.
• Print Debugging: Insert print statements throughout your code to display variable values and program flow, helping you identify where things go wrong.
• Perl Debugger: Use the built-in Perl debugger by running your script with the -d flag. This allows you to step through your code interactively.

By mastering the execution of Perl scripts, whether through the command line or an IDE, and understanding how to troubleshoot common issues, you’ll be well-equipped to tackle more complex scripting tasks. Happy coding!

Understanding Perl Modules and Libraries

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Perl is renowned for its rich ecosystem of modules and libraries that enhance its capabilities and simplify complex tasks. Understanding how to leverage these modules can significantly boost your productivity as a Perl developer and help you learn to launch Perl script effectively.

What are Modules and Why They’re Useful?

In Perl, a module is a reusable package of code that contains functions, variables, and other resources. Modules allow developers to organize code into manageable components, promoting reusability and modular design. Instead of writing everything from scratch, you can utilize existing modules to save time and effort.

Modules are beneficial for several reasons:

• Code Reusability: By using modules, you can avoid duplicating code across different scripts. If a particular functionality has been implemented in a module, you can simply include that module in your script, which helps in maintaining consistency and reducing errors.
• Community Contributions: Perl has a vibrant community that actively contributes to its ecosystem. Many developers have shared their modules through the Comprehensive Perl Archive Network (CPAN), which hosts thousands of modules covering a wide array of functionalities—from database interaction to web development.
• Simplified Development: Modules can simplify complex tasks. For instance, instead of writing intricate code for handling regular expressions or web requests, you can utilize specialized modules that encapsulate this functionality.

Installing and Using CPAN

The Comprehensive Perl Archive Network (CPAN) is a central repository where you can find, install, and manage Perl modules. Here’s how to get started with CPAN:

Installing CPAN

Most modern Perl installations come with CPAN pre-installed. To check if CPAN is available, open your terminal and type:

cpan

If it’s not installed, you can set it up by following the instructions in the Perl documentation or using your package manager (e.g., sudo apt-get install cpanminus on Debian-based systems).

Using CPAN

Once you have access to CPAN, you can install modules easily. Start by launching the CPAN shell:

cpan

To install a module, use the command:

install Module::Name

For example, to install the popular LWP::UserAgent module, you would type:

install LWP::UserAgent

To exit the CPAN shell, simply type:

exit

Using CPAN Minus

Alternatively, you can use cpanm, a simpler and faster interface for installing modules:

cpanm Module::Name

Example of Using a Popular Perl Module

One of the most commonly used Perl modules is LWP::UserAgent, which allows you to send HTTP requests and interact with web services. Here’s a simple example demonstrating how to use it to fetch the content of a webpage.

Install the Module (if you haven’t already)

cpanm LWP::UserAgent

Create a Script

Here’s a sample script that uses LWP::UserAgent to fetch and print the content of a webpage:

#!/usr/bin/perl

use strict;

use warnings;

use LWP::UserAgent;

my $url = ‘http://www.example.com’;  # URL to fetch

my $ua = LWP::UserAgent->new;        # Create a new UserAgent object

my $response = $ua->get($url);       # Send a GET request

if ($response->is_success) {

print $response->decoded_content; # Print the content of the response

} else {

die “Error fetching $url: ” . $response->status_line;

}

Run the Script

Save the script to a file, for example, fetch_example.pl, and execute it from the command line:

perl fetch_example.pl

If the script runs successfully, it will output the content of the specified webpage.

By understanding how to utilize Perl modules and libraries, along with tools like CPAN, you can greatly enhance your scripting capabilities and streamline your development process. This modular approach not only saves time but also allows you to build robust applications efficiently.

Practical Applications of Perl Scripts

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Perl is a versatile scripting language that excels in various domains, making it a powerful tool for developers and system administrators alike. Its strengths in text manipulation, data handling, and system interaction lend themselves to a wide array of practical applications. Here, we explore some of the most common use cases for Perl scripts in web development, system administration, data analysis, and automation.

Web Development

Perl has been a longstanding player in web development, particularly with the Common Gateway Interface (CGI). Although many developers now favor frameworks in other languages, Perl remains valuable for web applications, especially when leveraging frameworks like Dancer or Mojolicious. Perl scripts can handle HTTP requests, manage sessions, and interact with databases, making them suitable for building dynamic websites.

For instance, a Perl script can be used to create a simple web form that collects user input. The script processes the input and stores it in a database or sends an email. This functionality is invaluable for creating interactive websites, such as content management systems (CMS) or customer relationship management (CRM) tools.

System Administration

Perl is a powerful ally for system administrators. Its robust text processing capabilities make it ideal for writing scripts that automate routine tasks, such as log file analysis, user account management, and system monitoring. For example, a Perl script can parse log files to extract meaningful information, such as error messages or usage statistics. By automating this process, administrators can quickly identify issues and take corrective actions.

Additionally, Perl can be used to manage configuration files and automate system updates. With its ability to read and write files easily, system administrators can create scripts that update system settings or install necessary packages, streamlining operations and improving efficiency.

Data Analysis

In the era of big data, Perl’s ability to handle large datasets and perform complex data manipulations makes it a valuable tool for data analysis. Its built-in support for regular expressions allows for sophisticated pattern matching and text parsing, which are essential for cleaning and transforming data.

For example, a data analyst might use Perl to process CSV files, filter out irrelevant information, and aggregate data for reporting purposes. The script could read the file, apply transformations, and output the cleaned data into a new file or directly into a database. Additionally, Perl’s integration with databases through modules like DBI allows for seamless data retrieval and manipulation.

Automation

One of the most compelling use cases for Perl scripts is automation. Whether it’s automating backups, sending notifications, or generating reports, Perl can significantly reduce manual effort and increase productivity. For instance, a Perl script can be scheduled to run at regular intervals (using cron jobs on Unix-like systems) to back up important directories to a remote server.

Another common automation task is monitoring system performance. A Perl script can periodically check system metrics, such as CPU usage or disk space, and send alerts via email if certain thresholds are exceeded. This proactive approach helps system administrators maintain optimal performance and address potential issues before they escalate.

Best Practices for Writing Perl Scripts

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Writing effective Perl scripts requires adherence to certain best practices that enhance code quality, maintainability, and readability. By following these guidelines, you can create scripts that are easier to understand, debug, and share with others.

Coding Standards and Readability

Adopting a consistent coding style is crucial for improving the readability of your Perl scripts. Stick to common conventions, such as using meaningful variable names, following indentation rules, and avoiding overly complex expressions. For instance, use camelCase or snake_case for variable names and maintain consistent formatting throughout your script. This not only makes your code more approachable but also helps others who may work with your code in the future.

Tips for Maintaining and Organizing Perl Code

To keep your Perl code organized, consider the following strategies:

• Modular Design: Break your code into smaller, reusable subroutines or modules. This promotes code reuse and makes it easier to test and maintain individual components.
• File Structure: Organize your scripts and related files in a logical directory structure. Group related scripts together and use descriptive folder names to make navigation easier.
• Version Control: Utilize version control systems like Git to track changes, collaborate with others, and manage different versions of your code. This practice allows you to roll back changes if necessary and maintains a history of your development process.

Importance of Comments and Documentation

Comments play a vital role in enhancing code comprehension. Use comments to explain the purpose of complex code segments, document the expected input and output of functions, and provide context for your logic. Well-placed comments can significantly reduce the time spent deciphering your code later.

In addition to inline comments, consider maintaining external documentation. This can include an overview of your script’s functionality, installation instructions, and usage examples. Tools like Pod (Plain Old Documentation) in Perl allow you to create documentation directly within your scripts, ensuring that it stays up to date with your code changes.

Final Thoughts

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As you continue your journey with Perl, practice regularly and explore more advanced topics such as object-oriented programming, web frameworks, and database interactions. The more you experiment with Perl’s features and modules, the more proficient you will become.

For those looking to expand their tech knowledge beyond learning how to execute Perl script, be sure to check out Rayobyte’s blog. We regularly publish tutorials and insights on a variety of programming languages, tools, and best practices to help you stay ahead in the tech world.

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