Perlintro

   perl progname.pl

   #!/usr/bin/env perl

   #!/usr/bin/perl
   use strict;
   use warnings;

   print "Hello, world";

   # This is a comment

   print
   "Hello, world"
   ;

   # this would print with a linebreak in the middle
   print "Hello
   world";

   print "Hello, world";
   print 'Hello, world';

   print "Hello, $name\n"; # works fine
   print 'Hello, $name\n'; # prints $name\n literally

   print 42;

   print ("Hello, world\n");
   print "Hello, world\n";

       my $animal = "camel";
       my $answer = 42;

       print $animal;
       print "The animal is $animal\n";
       print "The square of $answer is ", $answer * $answer, "\n";

       print; # prints contents of $_ by default

       my @animals = ("camel", "llama", "owl");
       my @numbers = (23, 42, 69);
       my @mixed = ("camel", 42, 1.23);

       print $animals[0]; # prints "camel"
       print $animals[1]; # prints "llama"

       print $mixed[$#mixed]; # last element, prints 1.23

       if (@animals < 5) { ... }

       @animals[0,1]; # gives ("camel", "llama");
       @animals[0..2]; # gives ("camel", "llama", "owl");
       @animals[1..$#animals]; # gives all except the first element

       my @sorted = sort @animals;
       my @backwards = reverse @numbers;

       my %fruit_color = ("apple", "red", "banana", "yellow");

       my %fruit_color = (
       apple => "red",
       banana => "yellow",
       );

       $fruit_color{"apple"}; # gives "red"

       my @fruits = keys %fruit_colors;
       my @colors = values %fruit_colors;

   my $variables = {
   scalar => {
   description => "single item",
   sigil => '$',
   },
   array => {
   description => "ordered list of items",
   sigil => '@',
   },
   hash => {
   description => "key/value pairs",
   sigil => '%',
   },
   };
   print "Scalars begin with a $variables->{'scalar'}->{'sigil'}\n";

   my $var = "value";

   $var = "value";

   my $x = "foo";
   my $some_condition = 1;
   if ($some_condition) {
   my $y = "bar";
   print $x; # prints "foo"
   print $y; # prints "bar"
   }
   print $x; # prints "foo"
   print $y; # prints nothing; $y has fallen out of scope

       if ( condition ) {
       ...
       } elsif ( other condition ) {
       ...
       } else {
       ...
       }

       unless ( condition ) {
       ...
       }

       # the traditional way
       if ($zippy) {
       print "Yow!";
       }
       # the Perlish post-condition way
       print "Yow!" if $zippy;
       print "We have no bananas" unless $bananas;

       while ( condition ) {
       ...
       }

       until ( condition ) {
       ...
       }

       print "LA LA LA\n" while 1; # loops forever

       for ($i = 0; $i <= $max; $i++) {
       ...
       }

   The C style for loop is rarely needed in Perl since Perl provides the more friendly list scanning foreach loop.

       foreach (@array) {
       print "This element is $_\n";
       }
       print $list[$_] foreach 0 .. $max;
       # you don't have to use the default $_ either...
       foreach my $key (keys %hash) {
       print "The value of $key is $hash{$key}\n";
       }

   The foreach keyword is actually a synonym for the for keyword. See Foreach Loops in perlsyn.

       + addition
       - subtraction
       * multiplication
       / division

       == equality
       != inequality
       < less than
       > greater than
       <= less than or equal
       >= greater than or equal

       eq equality
       ne inequality
       lt less than
       gt greater than
       le less than or equal
       ge greater than or equal

       && and
       || or
       ! not

       = assignment
       . string concatenation
       x string multiplication
       .. range operator (creates a list of numbers)

   $a += 1; # same as $a = $a + 1
   $a -= 1; # same as $a = $a - 1
   $a .= "\n"; # same as $a = $a . "\n";

   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: $!";

   my $line = <$in>;
   my @lines = <$in>;

   while (<$in>) { # assigns each line in turn to $_
   print "Just read in this line: $_";
   }

   print STDERR "This is your final warning.\n";
   print $out $record;
   print $log $logmessage;

   close $in or die "$in: $!";

       if (/foo/) { ... } # true if $_ contains "foo"
       if ($a =~ /foo/) { ... } # true if $a contains "foo"

       s/foo/bar/; # replaces foo with bar in $_
       $a =~ s/foo/bar/; # replaces foo with bar in $a
       $a =~ s/foo/bar/g; # replaces ALL INSTANCES of foo with bar
       # in $a

       . a single character
       \s a whitespace character (space, tab, newline,
       ...)
       \S non-whitespace character
       \d a digit (0-9)
       \D a non-digit
       \w a word character (a-z, A-Z, 0-9, _)
       \W a non-word character
       [aeiou] matches a single character in the given set
       [^aeiou] matches a single character outside the given
       set
       (foo|bar|baz) matches any of the alternatives specified
       ^ start of string
       $ end of string

       * zero or more of the previous thing
       + one or more of the previous thing
       ? zero or one of the previous thing
       {3} matches exactly 3 of the previous thing
       {3,6} matches between 3 and 6 of the previous thing
       {3,} matches 3 or more of the previous thing

       /^\d+/ string starts with one or more digits
       /^$/ nothing in the string (start and end are
       adjacent)
       /(\d\s){3}/ three digits, each followed by a whitespace
       character (eg "3 4 5 ")
       /(a.)+/ matches a string in which every odd-numbered
       letter is a (eg "abacadaf")
       # This loop reads from STDIN, and prints non-blank lines:
       while (<>) {
       next if /^$/;
       print;
       }

       # a cheap and nasty way to break an email address up into parts
       if ($email =~ /([^@]+)@(.+)/) {
       print "Username is $1\n";
       print "Hostname is $2\n";
       }

   sub logger {
   my $logmessage = shift;
   open my $logfile, ">>", "my.log" or die "Could not open my.log: $!";
   print $logfile $logmessage;
   }

   logger("We have a logger subroutine!");

   my ($logmessage, $priority) = @_; # common
   my $logmessage = $_[0]; # uncommon, and ugly

   sub square {
   my $num = shift;
   my $result = $num * $num;
   return $result;
   }

   $sq = square(8);

Perlintro

Contents

NAME

DESCRIPTION

What is Perl?

Running Perl programs

Safety net

Basic syntax overview

Perl variable types

Scalars

Arrays

Hashes

Variable scoping

Conditional and looping constructs

if

while

for

foreach

Builtin operators and functions

Arithmetic

Numeric comparison

String comparison

Boolean logic

Miscellaneous

Files and I/O

Regular expressions

Simple matching

Simple substitution

More complex regular expressions

Parentheses for capturing

Other regexp features

Writing subroutines

OO Perl

Using Perl modules

AUTHOR

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