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168 lines
4.2 KiB
Markdown
168 lines
4.2 KiB
Markdown
---
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name: perl
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category: language
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language: perl
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filename: learnperl.pl
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contributors:
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- ["Korjavin Ivan", "http://github.com/korjavin"]
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---
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Perl 5 is a highly capable, feature-rich programming language with over 25 years of development.
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Perl 5 runs on over 100 platforms from portables to mainframes and is suitable for both rapid prototyping and large scale development projects.
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```perl
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# Single line comments start with a number sign.
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#### Perl variable types
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# Variables begin with a sigil, which is a symbol showing the type.
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# A valid variable name starts with a letter or underscore,
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# followed by any number of letters, numbers, or underscores.
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### Perl has three main variable types: $scalar, @array, and %hash.
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## Scalars
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# A scalar represents a single value:
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my $animal = "camel";
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my $answer = 42;
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# Scalar values can be strings, integers or floating point numbers, and
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# Perl will automatically convert between them as required.
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## Arrays
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# An array represents a list of values:
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my @animals = ("camel", "llama", "owl");
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my @numbers = (23, 42, 69);
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my @mixed = ("camel", 42, 1.23);
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## Hashes
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# A hash represents a set of key/value pairs:
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my %fruit_color = ("apple", "red", "banana", "yellow");
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# You can use whitespace and the "=>" operator to lay them out more nicely:
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my %fruit_color = (
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apple => "red",
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banana => "yellow",
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);
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# Scalars, arrays and hashes are documented more fully in perldata.
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# (perldoc perldata).
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# More complex data types can be constructed using references, which allow you
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# to build lists and hashes within lists and hashes.
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#### Conditional and looping constructs
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# Perl has most of the usual conditional and looping constructs.
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if ($var) {
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...
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} elsif ($var eq 'bar') {
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...
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} else {
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...
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}
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unless (condition) {
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...
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}
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# This is provided as a more readable version of "if (!condition)"
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# the Perlish post-condition way
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print "Yow!" if $zippy;
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print "We have no bananas" unless $bananas;
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# while
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while (condition) {
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...
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}
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# for loops and iteration
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for (my $i = 0; $i < $max; $i++) {
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print "index is $i";
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}
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for (my $i = 0; $i < @elements; $i++) {
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print "Current element is " . $elements[$i];
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}
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for my $element (@elements) {
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print $element;
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}
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# implicitly
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for (@elements) {
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print;
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}
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# the Perlish post-condition way again
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print for @elements;
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#### Regular expressions
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# Perl's regular expression support is both broad and deep, and is the subject
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# of lengthy documentation in perlrequick, perlretut, and elsewhere.
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# However, in short:
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# Simple matching
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if (/foo/) { ... } # true if $_ contains "foo"
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if ($a =~ /foo/) { ... } # true if $a contains "foo"
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# Simple substitution
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$a =~ s/foo/bar/; # replaces foo with bar in $a
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$a =~ s/foo/bar/g; # replaces ALL INSTANCES of foo with bar in $a
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#### Files and I/O
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# You can open a file for input or output using the "open()" function.
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open(my $in, "<", "input.txt") or die "Can't open input.txt: $!";
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open(my $out, ">", "output.txt") or die "Can't open output.txt: $!";
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open(my $log, ">>", "my.log") or die "Can't open my.log: $!";
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# You can read from an open filehandle using the "<>" operator. In scalar
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# context it reads a single line from the filehandle, and in list context it
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# reads the whole file in, assigning each line to an element of the list:
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my $line = <$in>;
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my @lines = <$in>;
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#### Writing subroutines
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# Writing subroutines is easy:
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sub logger {
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my $logmessage = shift;
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open my $logfile, ">>", "my.log" or die "Could not open my.log: $!";
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print $logfile $logmessage;
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}
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# Now we can use the subroutine just as any other built-in function:
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logger("We have a logger subroutine!");
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```
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#### Using Perl modules
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Perl modules provide a range of features to help you avoid reinventing the wheel, and can be downloaded from CPAN (http://www.cpan.org/). A number of popular modules are included with the Perl distribution itself.
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perlfaq contains questions and answers related to many common tasks, and often provides suggestions for good CPAN modules to use.
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#### Further Reading
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- [perl-tutorial](http://perl-tutorial.org/)
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- [Learn at www.perl.com](http://www.perl.org/learn.html)
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- [perldoc](http://perldoc.perl.org/)
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- and perl built-in : `perldoc perlintro`
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