Input Perl Tutorial - · 2011-03-22 · Perl Tutorial Erik Hjelmås Variables Arrays...

Perl Tutorial

Erik Hjelmås

VariablesArrays

Structures/Classes

Command-line args

InputInput

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Conditionsif/else

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Switch/case

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Foreach

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Perl only

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Perl Tutorial

Erik Hjelmås

March 22, 2011

Perl Tutorial

Erik Hjelmås

VariablesArrays

Structures/Classes

Command-line args

InputInput

System commands

Conditionsif/else

Operators

Switch/case

IterationFor

Foreach

While

Math

Functions

RegExpPerl example

Perl only

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Credits(OUSTERHOUT, J., “Scripting: Higher-Level Programming for the 21st Century”,

IEEE Computer, Vol. 31, No. 3, March 1998, pp. 23-30.)

Perl Tutorial

Erik Hjelmås

VariablesArrays

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WARNING!

The following presentation is NOT meant to be acomprehensive/complete tour of the Perl language.

The purpose is to get you started with some basic programconstructions which you will recognize based onsome-sort-of-programming-background.

At the end of the presentation you will find pointers to morecomprehensive material.

Perl Tutorial

Erik Hjelmås

VariablesArrays

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Practice

You need a GNU/Linux distribution (e.g. Ubuntu) running ona physical or virtual machine with working access to theinternet, and with perl and wget installed.

Log in and open a terminal window, download the examplesas we go along with

wget http :// www.hig.no/~ erikh/tutorial -perl/ FILENAME

Perl Tutorial

Erik Hjelmås

VariablesArrays

Structures/Classes

Command-line args

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Hello World

#!/ usr/bin/perl# hello.pl

print "Hello world !\n";

make executable and execute:

chmod +x hello.pl./ hello.pl

or direct from command line

perl -e 'print "hello world !\n";'

Perl Tutorial

Erik Hjelmås

VariablesArrays

Structures/Classes

Command-line args

InputInput

System commands

Conditionsif/else

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Switch/case

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RegExpPerl example

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Single Variables

#!/ usr/bin/perl# single -var.pl

$firstname =Mysil;$lastname = Bergsprekken ;$fullname =" $firstname $lastname ";print "Hello $fullname , may I call you $firstname ?";

Scalars start with a $

Perl Tutorial

Erik Hjelmås

VariablesArrays

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Arrays

One-dimensional arrays:

#!/ usr/bin/perl# array.pl

@os =("linux", " windows ");$os [2]="mac";print $os [1], "\n"; # print windowsprint @os , "\n"; # print entire arrayprint $#os+1, "\n"; # length of array

Arrays start with a @

Perl Tutorial

Erik Hjelmås

VariablesArrays

Structures/Classes

Command-line args

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Conditionsif/else

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Associative Arrays

#!/ usr/bin/perl# assoc -array.pl

%user =(" frodeh " => "Frode Haug","ivarm" => "Ivar Moe"

);$user{" lailas "}="Laila Skiaker ";print $user{"ivarm"}, "\n"; # print Ivar Moeprint %user , "\n"; # print entire arrayprint $#user , "\n"; # nonsense ! instead do:print scalar keys %user , "\n";

Associative arrays start with a %

Perl Tutorial

Erik Hjelmås

VariablesArrays

Structures/Classes

Command-line args

InputInput

System commands

Conditionsif/else

Operators

Switch/case

IterationFor

Foreach

While

Math

Functions

RegExpPerl example

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Structures/Classes

Perl has objects which can simulate structs:

#!/ usr/bin/perl# struct .pl

use Class :: Struct ;struct host => { os => '$',

sw => '@',user => '%' };

$spock = new host;$spock ->os("linux");$spock ->sw(["gcc", "flex", "vim"]);$spock ->user ({" frodeh " => "Frode Haug",

" monicas " => " Monica Strand "});print $spock ->os , "\n";print $spock ->sw(2), "\n";print $spock ->user(" monicas "), "\n";

Perl Tutorial

Erik Hjelmås

VariablesArrays

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Command-Line Arguments

All command-line arguments in @ARGV

Scriptname in $0, arguments in $ARGV[0], $ARGV[1], ...

#!/ usr/bin/perl# cli -args.pl

print "I am $0 , and have ", $# ARGV +1," arguments first is $ARGV [0]\n";

Perl Tutorial

Erik Hjelmås

VariablesArrays

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Command-line args

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Input From User

#!/ usr/bin/perl# input -user.pl

print "Say something here: ";$something =<STDIN >;print "you said $something ";

The operator <FD> reads one line (or more dependent onthe context, more on that in a few slides) from thefiledescriptor FD

Perl Tutorial

Erik Hjelmås

VariablesArrays

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Input From STDIN

Same way, commonly without a print first

#!/ usr/bin/perl# input -stdin.pl

$something =<STDIN >;print "you said $something ";

can be executed as

echo "hey hey!" | ./ input -stdin.pl

Perl Tutorial

Erik Hjelmås

VariablesArrays

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Context Dependent OperatorsThe operator <...> in scalar context

#!/ usr/bin/perl# context - scalar .pl

$array = <STDIN >;print $array ;

will read one line, while in array context will read an entirearray

#!/ usr/bin/perl# context -array.pl

@array = <STDIN >;print @array ;

So, some operators behave differently in scalar and arraycontext.

Perl Tutorial

Erik Hjelmås

VariablesArrays

Structures/Classes

Command-line args

InputInput

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Input From Files or Pipes

#!/ usr/bin/perl# input -files -pipes.pl

open(FD ,"<hello.pl") || die ("hello.pl: $!");@fil=<FD >; # array contextprint @fil;close(FD);

# or open a file descriptor to a pipe

open(FD ,"ls -1 |") || die ("ls -1: $!");@fil=<FD >; # array contextprint @fil;close(FD);

Perl Tutorial

Erik Hjelmås

VariablesArrays

Structures/Classes

Command-line args

InputInput

System commands

Conditionsif/else

Operators

Switch/case

IterationFor

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Math

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Input from System Commands

#!/ usr/bin/perl# input - commands .pl

$kernel =`uname -sr `;chomp $kernel ;print "I am running on $kernel in ",`pwd `;

chomp removes linebreak (\n on Unix/Linux, \r\n onWindows), commonly used when input read with <FD>(where FD is a file descriptor)

Perl Tutorial

Erik Hjelmås

VariablesArrays

Structures/Classes

Command-line args

InputInput

System commands

Conditionsif/else

Operators

Switch/case

IterationFor

Foreach

While

Math

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RegExpPerl example

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if/else

#!/ usr/bin/perl# if.pl

if ($# ARGV +1 != 1) {print "usage: $0 <argument >\n";

}

can also be written as

#!/ usr/bin/perl# if -short.pl

print "usage: $0 <argument >\n" if ($# ARGV +1 != 1);

Perl Tutorial

Erik Hjelmås

VariablesArrays

Structures/Classes

Command-line args

InputInput

System commands

Conditionsif/else

Operators

Switch/case

IterationFor

Foreach

While

Math

Functions

RegExpPerl example

Perl only

Case

Credits

Numeric Comparison

Operator Meaning< Less than> Greater than<= Less than or equal to>= Greater than or equal to<=> Comparison== Equal to!= Not equal to

Perl Tutorial

Erik Hjelmås

VariablesArrays

Structures/Classes

Command-line args

InputInput

System commands

Conditionsif/else

Operators

Switch/case

IterationFor

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Math

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RegExpPerl example

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String Comparison

Operator Meaninglt Less thangt Greater thanle Less than or equal toge Greater than or equal tocmp Comparisoneq Equal tone Not equal to

Perl Tutorial

Erik Hjelmås

VariablesArrays

Structures/Classes

Command-line args

InputInput

System commands

Conditionsif/else

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Switch/case

IterationFor

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File Tests

Operator Meaning-e Exists-s Not zero size-f Regular file-d Directory-l Symbolic link-u Set-user-id (SetUID) flag set

Perl Tutorial

Erik Hjelmås

VariablesArrays

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IterationFor

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RegExpPerl example

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Boolean

Operator Meaning! Not&& And|| Or

Perl Tutorial

Erik Hjelmås

VariablesArrays

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Numerical or String Compare

#!/ usr/bin/perl# if -num - string .pl

if ($# ARGV +1 != 2) { # numerical cmpprint "usage: $0 <argument > <argument >\n";exit 0;

} elsif ($ARGV [0] == $ARGV [1]) { # numerical cmpprint "$ARGV [0] is arithm . equal to $ARGV [1]\n";

} else {print "$ARGV [0] and $ARGV [1] arithm . differs \n";

}if ($ARGV [0] eq $ARGV [1]) { # string cmp

print "$ARGV [0] is string equal to $ARGV [1]\n";} else {

print "$ARGV [0] and $ARGV [1] string differs \n";}print "$ARGV [0] is also a file\n" if (-f $ARGV [0]);

Perl Tutorial

Erik Hjelmås

VariablesArrays

Structures/Classes

Command-line args

InputInput

System commands

Conditionsif/else

Operators

Switch/case

IterationFor

Foreach

While

Math

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RegExpPerl example

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Boolean example

#!/ usr/bin/perl# if -bool.pl

if ((1==2) && (1==1) || (1==1)) {print "And has precedence \n";

} else {print "Or has precedence \n";

}

# force OR precedence :

if ((1==2) && ((1==1) || (1==1))) {print "And has precedence \n";

} else {print "Or has precedence \n";

}

Perl Tutorial

Erik Hjelmås

VariablesArrays

Structures/Classes

Command-line args

InputInput

System commands

Conditionsif/else

Operators

Switch/case

IterationFor

Foreach

While

Math

Functions

RegExpPerl example

Perl only

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Switch/Case

#!/ usr/bin/perl# switch .pl

use Switch ;%short = ( yes => "y", nope => "n" );$ans = <STDIN >;chomp $ans;switch ($ans) {

case m/yes/ { print "yes !\n"; next; }case m/nope/ { print "nope !\n"; }case (% short) { print " $short {$ans }\n"; }print "$ans ???\n";

}

Perl Tutorial

Erik Hjelmås

VariablesArrays

Structures/Classes

Command-line args

InputInput

System commands

Conditionsif/else

Operators

Switch/case

IterationFor

Foreach

While

Math

Functions

RegExpPerl example

Perl only

Case

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For loop#!/ usr/bin/perl# for.pl

for ($i =1;$i <=3; $i ++) {print "$i\n";

}

# something more useful :

@file=`ls -1`;for ($i =0;$i <=$# file;$i ++) {

chomp $file[$i];if (-f $file[$i]) {

print "$file[$i] is a regular file\n";} else {

print "$file[$i] not regular file\n";}

}

Perl Tutorial

Erik Hjelmås

VariablesArrays

Structures/Classes

Command-line args

InputInput

System commands

Conditionsif/else

Operators

Switch/case

IterationFor

Foreach

While

Math

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RegExpPerl example

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Foreach loop

#!/ usr/bin/perl# foreach .pl

foreach $i (`ls -1`) {print "$i";

}

# with associative arrays :

%user =(" frodeh " => "Frode Haug"," monicas " => " Monica Strand ","ivarm" => "Ivar Moe"

);foreach $key (keys %user) {

print "$user{$key }\n";}

Perl Tutorial

Erik Hjelmås

VariablesArrays

Structures/Classes

Command-line args

InputInput

System commands

Conditionsif/else

Operators

Switch/case

IterationFor

Foreach

While

Math

Functions

RegExpPerl example

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While

We want to read from STDIN and do stuff line by line

#!/ usr/bin/perl# while.pl

# This is myscript .pl$i =0;while(<STDIN >) {

chomp;$foo[$i]=$_;$i ++;

}print "size of foo " ,$# foo +1,"\n";

$ ls -1 | ./ myscript .plsize of foo is 20

Perl Tutorial

Erik Hjelmås

VariablesArrays

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RegExpPerl example

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Operators

Operator Meaning+ Add- Subtract* Multiply/ Divide% Modulus** Exponent

#!/ usr/bin/perl# math.pl

print "3+5 is " ,3+5,"\n";

Perl Tutorial

Erik Hjelmås

VariablesArrays

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Functions

#!/ usr/bin/perl# func.pl

# declare :sub add {

my ($a , $b) = @_;print "$a+$b is ",$a+$b ,"\n";

}# use:add (5.12 ,2.56);

Perl Tutorial

Erik Hjelmås

VariablesArrays

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Regular expressions intro 1/5

Special/Meta-characters:

\ | ( ) [ ] { } ^ $ * + ? .

These have to be protected with \, e.g.http://www\.hig\.no

To match c:\temp, you need to use the regexc:\\temp. As a string in C++ source code, thisregex becomes "c:\\\\temp". Four backslashesto match a single one indeed.

(from http://www.regular-expressions.info/characters.html):

http://www.regular-expressions.info/characters.html

http://www.regular-expressions.info/characters.html

Perl Tutorial

Erik Hjelmås

VariablesArrays

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Describing characters:

Operator Meaning. Any single character

[abcd] One of these characters[^abcd] Any one but these characters

[a-zA-Z0-9] A character in these ranges\w, \W A word, A not-word character\d, \D A digit, A not-digit character

\b A word boundary

Perl Tutorial

Erik Hjelmås

VariablesArrays

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Grouping:

Operator Meaning() Group| OR

Anchoring:

Operator Meaning^ Beginning of line$ End of line

Perl Tutorial

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Repetition operators/Modifiers/Quantifiers:

Operator Meaning? 0 or 1 time* 0 or more times+ 1 or more times

{N} N times{N,} At least N times{N,M} At least N but not more than M

Perl Tutorial

Erik Hjelmås

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Finding URLs in HTML:(mailto|http)://[^"]*

Each line should be an email address:^[A-Za-z0-9._-]+@[A-Za-z0-9.-]+$

Perl Tutorial

Erik Hjelmås

VariablesArrays

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Command-line args

InputInput

System commands

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Perl example

#!/ usr/bin/perl# regexp .pl

while(<STDIN >) {chomp;if (m/^([A-Za -z0 -9._ -]+@([A-Za -z0 -9. -]+))$/) {

print "Valid email $1\n";print " Domain is $2\n";

} else {print " Invalid email address !\n";

}}

Perl Tutorial

Erik Hjelmås

VariablesArrays

Structures/Classes

Command-line args

InputInput

System commands

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IterationFor

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Advanced stuff

See Comprehensive Perl Archive Network (CPAN) at

http://www.cpan.org

for everything you can do with Perl

http://www.cpan.org

Perl Tutorial

Erik Hjelmås

VariablesArrays

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Command-line args

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Let’s solve this together

Write a script which

• reads urls from STDIN (typically piped into this script,one url on each line)

• retrieves the document located at the url• searches the document line-by-line with a regexp

supplied on the command line• output nicely formatted relevant info if matches found

Perl Tutorial

Erik Hjelmås

VariablesArrays

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Command-line args

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Getting started

1 <loop: lines in urlfile>2 <retrieve urls to files>1 <end loop>

1 <loop: files>3 <loop: lines in each file>3 <if match>4 <nice output>3 <end loop>1 <end loop>

Perl Tutorial

Erik Hjelmås

VariablesArrays

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Nice Script, but ...

Is the script efficient?

• time it, analyze its resource usage (I/O usage?)

Is the script secure?

• how will it be used? system program with privileges?• input validation?• what are its powers?• how can it fail?

Perl Tutorial

Erik Hjelmås

VariablesArrays

Structures/Classes

Command-line args

InputInput

System commands

Conditionsif/else

Operators

Switch/case

IterationFor

Foreach

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Math

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Credits

http://www.cpan.org/T. Christiansen, R. L. Schwartz and L. Wall, "Programming Perl, Second Edition",O’Reilly Media, 1996.http://www.misc-perl-info.com/http://www.cs.cf.ac.uk/Dave/PERL/http://www.perl.orghttp://www.tutorialspoint.com/perl/J. Ousterhout, "Scripting: Higher-Level Programming for the 21st Century," IEEEComputer, Vol. 31, No. 3, March 1998, pp. 23-30.Jon Thingvold’s “Drift av flerbrukersystemer”, kompendium 1999.http://www.regular-expressions.info/

http://www.cpan.org/

http://www.misc-perl-info.com/

http://www.cs.cf.ac.uk/Dave/PERL/

http://www.perl.org

http://www.tutorialspoint.com/perl/

http://www.regular-expressions.info/

Input Perl Tutorial - · 2011-03-22 · Perl Tutorial Erik Hjelmås Variables Arrays...

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