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| diff --git a/perl.html.markdown b/perl.html.markdown new file mode 100644 index 00000000..18339dde --- /dev/null +++ b/perl.html.markdown @@ -0,0 +1,149 @@ +--- +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 hash. + + +#### Perl variable types + +#  Variables begin with the $ symbol. +#  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: scalars, arrays, and hashes. + +## 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 $bananas; + +#  while +  while ( condition ) { +                   ... +               } + + +# for and foreach +for ($i = 0; $i <= $max; $i++) { +                   ... +               } + +foreach (@array) { +                   print "This element is $_\n"; +               } + + +#### 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` | 
