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