Perl

Reading

http://www.perl.org/books/beginning-perl/

Perl

Pathologically Eclectic Rubbish Lister

Larry Wall wrote it.

variables

the three types of variables in Perl are:

scalars = numbers, strings, or references    denoted $ 
arrays = sequentially-numbered lists of scalars     denoted @
hashes.= key-referenced lists of scalars     denoted %

operators

Operator                   Num     Str
--------------------------------------
Equal                      ==      eq
Not equal                  !=      ne
Less than                   <      lt
Greater than                >      gt
Less than or equal to      <=      le
Greater than or equal to   >=      ge

man pages

perl      - overview               perlfaq   - frequently asked questions
perltoc   - doc TOC                perldata  - data structures
perlsyn   - syntax                 perlop    - operators and precedence
perlrun   - execution              perlfunc  - builtin functions
perltrap  - traps for the unwary   perlstyle - style guide

"perldoc" and "perldoc -f"

cpan

Comprehensive perl archive network

Perl kurs

Christer Ekholm
First two letters and first letter of last name@init.se
TIMTOWTDI (There Is More Than One Way To Do It)

Dictionary

regexp		regular expression . a* a? ^a a$,perls RE för andra.
semantik	meaning that is expressed in a language and words
notation	ways to represent a mathematical equation
analogi		motsvarighet, nagot svart beskrivs enkelt
iteration	upprepning
deklarera	förklara
definera	definera subrutiner
context		sammanhang
explicit	uttryckligen
implicit	underförstått
logiska operatorer	and,or,not,||,&&,!
aritmetisk	+-/*
bitoperatorer	AND,OR,XOR,leftand right shift.
re		reguljära utryck, mönsterpassning.
statement	If functions are the verbs of Perl, then statements are the sentences.
scalar literal constant	varaiable that cant change
interpolated	Variable has been expanded
Boolean operators	The idea of combining values that represent truth and falsehood is called Boolean logic,after George Boole, who invented the concept in 1847, and we call the operators that do the combining 'Boolean operators'.

boolean operators

numeriska	sträng
==	!=	eq 	ne
<	>	lt	gt
<=	>=	le	ge
jämförelse operatörer	

numeriska sträng

<=>		cmp
citatecken	"" variabler expanderar qq,  variabler oförändrade q, `` exekveras qx

#!/usr/bin/perl
use warnings;
print"Is two equal to four? ", 2 == 4, "\n";
print "OK, then, is six equal to six? ", 6 == 6, "\n";
print"So, two isn't equal to four? ", 2 != 4, "\n";
print"Five is more than six? ", 5 > 6, "\n";
print "Seven is less than sixteen? ", 7 < 16, "\n";
print "Two is equal to two? ", 2 == 2, "\n";
print "One is more than one? ", 1 > 1, "\n";
print "Six is not equal to seven? ", 6 != 7, "\n";
print"Seven is less than or equal to sixteen? ", 7 <= 16, "\n";
print "Two is more than or equal to two? ", 2 >= 2, "\n";

Is two equal to four?
OK, then, is six equal to six? 1
So, two isn't equal to four? 1
Five is more than six?
Seven is less than sixteen? 1
Two is equal to two? 1
One is more than one?
Six is not equal to seven? 1
Seven is less than or equal to sixteen? 1
Two is more than or equal to two? 1

print "1 <= 0 => -1", "\n";
print "Compare six and nine? ", 6 <=> 9, "\n";
print "Compare seven and seven? ",7 <=> 7, "\n";
print "Compare eight and four? ", 8 <=> 4, "\n";

print 6 > 3 && 12 > 4, "\n"; # 1
print 9 > 7 || 6 > 8, "\n";  # 1
print !(2>3), "\n";          # 1
print !2>3, "\n";            # 0

How to get information

perldoc -f variabler	Show help page for variables
perldoc -f -X		Show file handle test.
perldoc perlform	Format information
perldoc Getopt::Long	Show help for Getopt
perldoc -q		Letar i perl faq
perldoc perlmodlib	Lista inbyggda moduler
perldoc perlpod

Debug

emacs M-x perldb	Debugga perl i emacs
perl -d:ptkdb /scrpt	Debugga perl  

Perl code

use strict;	explesist namnge package variable
use warning;	show warning messages
perl -w		show warning messages
use Getopt::Long:	Use getoptions module

package mypkg; change package

Perl Oneliners:

perl -ne 'print if /a/'			Grep all lines containing a. (-n create a loop) (-e, allows you to define Perl code to be executed by the compiler)
perl -e 'print join("\n",@INC),"\n"'	Var söker perl efter moduler
perl -c kod.pl				Kontrollera koden.

regex

.		one key
^		beginning of line
$		end of line
/^[xfi]/	Starting with one x or f or i
/^[h-j]/	Starting with one h or i or j
()		Deluttryck
quantifier	how much a string matches.
?		Noll eller en gång
a*		a with 0 to unlimit a
a+		one or more a
{m}		exackt m ggr
{m,}		minst m ggr
{m,n}		minst m max n ggr
=~ m|^abc|	matchar abc i början
.+?		matchar så lite som möjligt
modifierare	
/i/i		matchar i case insensitiv
a.b		a any key b
^a.c$		starting with a any key end with c
X1*		X1 folles by 0 to many 1
^[]abc]		strings starting with any of ]abc
[^zxy]		Does not have any of zxy in possition
a{8}		aaaaaaaa
uttr{m,n}	uttr förekommer mellan m och n gånger
^ *$		empty line or only blanks

Special meaning

$		skalär
@		lista
%		hash, associativa vektorer
$#		maximun index in list
$@		string that eval generates.
\s		remove space,tab,lf...
\s+		godtyckligt
\l		Convert to lower case.
$_		Default output input
$$		processid
$?		exit status
@_		variable to send to subroutin
@ARGV		argument list. ('-v','-g','10','logfile')
$|=1;		dont flush output stty
$"=',';		dubbelfnuttade listor
_		fil operatorer och stat kan återänväda stat förfrågan.
$.		Radräknare
$1		Delutryck som matchade
local $/	
@INC		directories to find per modules, add directory export PERL5LIB=/bin:/hej

&sub		subrutin
$var2=\$var	refere var2 to var
@list('a',1,$a)	add tree elements to list
@list([@odd])	add copy of list called anonymous list
$list[5]	6 possition in list
@list = qw<Jan Feb>;	Generate list

$hash{'var'}	element with index var in hash
%hash{'a'}='5';	add key a value 5
if (exist($hash{a})){	run if key a exist i hash hash
delete($hash{'a'});	delete key a fron hash
split(' ',$str);	split list output whith ' '

my		lexikal variabel, lokal variabel
$main::var	main variabel

styrstrukturer

• iterationer

while [EXPR] BLOCK
until [EXPR] BLOCK
do BLOCK while [EXPR]
do BLOCK until [EXPR]
for VAR (EXPR) BLOCK
for (EXPR1; EXPR2; EXPR3) BLOCK

• selection

if (EXPR) BLOCK
if (EXPR) BLOCK1 elsif (EXPR2) BLOCK2... elxe BLOCKn
unless (EXPR) BLOCK

filehandels

STDIN,STDOUT,STDERR

sträng list konverteringar

join (EXPR,LIST)
@words = ("merry", "go", "round");
$str = join("-",@words);

split (REGEXP,EXPR)
$str = "sys:x:3:3:sys:/dev:/bin/sh";
@fields = split (/:/, $str);
for $rad ( @fields ){
    print "$rad\n";
}

sub usage {
    print "use this command with optional -v"
}

&subrutin(15,101,38)	arguments are sent to a subroutin as a list

command options

use Getopt::Long;
my %opts;
GetOptions(\%opts,'v','g=i') || &usage;
print "$opts{g}\n";

sub usage {
    print STDERR "Usage: option.pl [-v][-g n]";
    exit 1;
}

globala symboltabellen

foreach my $var ( keys %main::){
    print "$var\n";

formatting.

my $rand1 = int(rand (90));
my $rand2 = int(rand (10));
my $rand3 = int(rand (50));
printf ("%6d %6d %6d\n",$rand1,$rand2,$rand3);

filehandlers

print "Who are you?\n";
my $name = <STDIN>;
chomp($name);
print "You are $name!!!\n";

print contents of file.

my $file = "/tmp/test";
open(IN,'<',$file) || die "open $file failed: $!";
# Loopa på rader i infilen.
while ( <IN> ) {
    print $_;
}

diamond operator @ARGV

#!/usr/bin/perl
while (<>){
    print;
}

list files

opendir(DIR,"/etc");
my @files = sort grep(/x/,readdir(DIR));
closedir(DIR);

user external program

open(PING,'-|','/bin/ping -c 3 pizza');
while (defined(my $ping = <PING>)){
    print "$ping";
}
close PROG;

Backslash magic

\t          tab                   (HT, TAB)
\n          newline               (LF, NL)
\r          return                (CR)
\f          form feed             (FF)
\a          alarm (bell)          (BEL)
\e          escape (think troff)  (ESC)
\033        octal char (think of a PDP-11)
\x1B        hex char
\c[         control char
\l          lowercase next char (think vi)
\u          uppercase next char (think vi)
\L          lowercase till \E (think vi)
\U          uppercase till \E (think vi)
\E          end case modification (think vi)
\Q          quote (disable) pattern metacharacters till \E

\w  Match a "word" character (alphanumeric plus "_")
\W  Match a non-word character
\s  Match a whitespace character
\S  Match a non-whitespace character
\d  Match a digit character
\D  Match a non-digit character

keywords

Words that perl is already aware of are called keywords, and they come in several classes.

print is one example of the class called functions

functions

hex() Convert Hexadecimal to number
oct() Convert Octal to number
ord() character's value

control keywords

There are also control keywords, such as if and else.

block

We can also group together a bunch of statements into a block – which is a bit like a paragraph – by

surrounding them with braces: {...}

number systems.

print 255,
octal print 0377,
binary print 0b11111111,
hexadecimal print 0xFF,

Alternative Delimiters

the first acting like a single-quoted string and the second, like a double-quoted string.

q// and qq//,

here documents

print<<EOF;
This is a here-document. It starts on the line after the two arrows,
and it ends when the text following the arrows is found at the beginning
of a line, like this:
EOF

Write label with 'EOF' and her text will be single quoted.

arithmetic Operator

#!/usr/bin/perl
use warnings;
print "21 - 25 is: ", 25 - 21, "\n";
print "4 + 13 - 7 is: ", 4 + 13 - 7, "\n";
print "7 * 15 is ", 7 * 15, "\n";
print "249 / 3 is ", 249 / 3, "\n";
print 3 + 7 * 15, "\n";
print ((3 + 7) * 15);

21 - 25 is: 4
4 + 13 - 7 is: 10
7 * 15 is 105
249 / 3 is 83
108
150

lazy evaluation

Perl uses a technique called lazy evaluation. As soon as it knows the answer to the question, it stops working.

4 >= 2 and print "Four is more than or equal to two\n";

string operators

concatenation operator   print "Print " . "one ". "string " . "here" . "\n";
repetition operator      print "Andreas halfface! "x3, "\n"; # Andreas halfface! Andreas halfface! Andreas halfface!