mirror of
https://github.com/adambard/learnxinyminutes-docs.git
synced 2024-11-23 06:03:07 +03:00
148 lines
4.1 KiB
Markdown
148 lines
4.1 KiB
Markdown
---
|
|
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 symbol.
|
|
|
|
|
|
#### 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`
|