introduction to perl lecturer: prof. andrzej (aj) bieszczad email: [email protected] phone:...

Introduction to Perl

Lecturer: Prof. Andrzej (AJ) BieszczadEmail: [email protected]

Phone: 818-677-4954

“UNIX for Programmers and Users”Third Edition, Prentice-Hall, GRAHAM GLASS, KING ABLES

Slides partially adapted from Kumoh National University of Technology (Korea) and NYU


Prof. Andrzej (AJ) Bieszczad Email: [email protected] Phone: 818-677-4954 2

What is Perl?• Practical Extraction and Report Language

• Written in 1986 by Larry Wall

• Influenced from awk, sed, and C Shell

• Similar to ksh93, python, tcl, javascript

• Widely used for CGI scripting

• Freely available



Running Perl in UNIX• Explicit invocation of a program

$ perl [options] program [arguments]

• Using the #! Directive in program

$ program [arguments]

• Command line expression

$ perl –e ’print ”hello\n”;’

• Debugging mode (opens a CLI debugger - similar to gdb, dbx, jdb, etc.)

$ perl -d program [args]



Perl Example

#!/usr/bin/perl -w # THIS IS A COMMENT: -w issues warningsprint “What is your favorite color? “;$color = <STDIN>;chomp($color);if ($color eq ‘blue’){print “That is my favorite! \n”;

}elsif ($color =~ /black/){print “ I do like $color for my shoes\n”;

}else{print “$color is a nice choice \n”;

}



Data Types• Basic data types: scalars, indexed arrays of scalars (lists), and associative arrays.

• Scalars are strings or numbers depending on context.

• Type of variable determined by special leading character:

$ scalar@ indexed array% associative array& function

• All data types have separate name spaces



Data Types Examples• Scalars:

$str = “The world is round” ; # string variable$num = 134.99; # numeric variable

• Arrays

@students =(“Mike”, “Lisa”, “John”);print $students[0]; # print Mike$students[3]= “Julie”; # add a new element$size = @students; # size of the array (== 4)@students = (); # empty array

• Hashes

%emp =(“Julie”, “President”, “Mary”, “VP”);print $emp {“Julie”}; # print “President”$emp{“John”} = “controller”; # add an element



Special Scalar VariablesImportant special variable:

$_ default pattern for operators

Plenty fo other variable:

$0 name of the currently running script

$$ the current PID

$? status of last pipe or system call

$. the current line number of last input

$] the version of perl being used

$< the real uid of the process

$> the effective uid of the process



Special Array Variables@ARGV command line arguments

@INC search path for modules

@_ default for split and subroutine parameters

%ENV current environment

%SIG used to set signal handlers

sub trapped {print STDERR “Interrupted!\n”;exit 1;

}$SIG{’INT’} = ’trapped’;



Operators• Perl uses all of C’s operators (except type casting and pointer operators), and adds:

• exponentiation: **, **=

• range operator: ..

@new = @old[30..50];print 1 .. 9;

• string concatenation: . , .=

$x = $y . &frob(@list) . $z;$x .= ”\n”;

• string repetitor operator: x

“fred” x 3 # is fredfredfred



Numeric and String comparison operators

Comparison Numeric String

equal == eq

not equal != ne

less than < lt

greater than > gt

less than or equal to <= le

greater than or equal to >= ge



Flow Control• Unlike C, blocks always require braces

• unless and until are just if and while negated

if (EXPR) BLOCK else BLOCK

if (EXPR) BLOCK elsif (EXPR) BLOCK else BLOCK

while (EXPR) BLOCK

do BLOCK while EXPR

for (EXPR; EXPR; EXPR) BLOCK

foreach $VAR (LIST) BLOCK

• For readability, if, unless, while and until may be used as trailing statement modifiers:

return –1 unless $x > 0;&myfunction or die

• Uses next and last rather than C’s continue and break. Also contains redo to repeat loop iteration



Flow Control Examples# print an arrayfor ($i = 0; $i < @myarray; $i++) { # @myarray is the number of elements print “$myarray[$i]\n”;}

# print all element of an array until the one that is negativeforeach $element (@myarray) { last if $element < 0; print “$element\n”;}

# check if password file existsif (-f /etc/passwd) { print “file exists\n”}



Flow Control Examples # reverse foo$n = @foo; for ($i=0; $i < $n/2; $i++) {

$temp = $foo[$i];$foo[$i] = $foo[$n-1-$i];$foo[$n-1-$i] = $temp;

}

# find power of 2 larger than a numberprint "Enter a number: ";$num = <STDIN>;$power = 1;$power *=2 until ($power >= $num);print "next power of 2 is $power\n";



Another Flow Control Example# ask for a non-empty name{ print("What is your name? "); $name = <STDIN>; chop($name);

if (! length($name)) { print("Please try again\n"); redo; }

print("Thank you, " . uc($name) . "\n");}

do { print("What is your name? "); $name = <STDIN>; chomp($name);

if (! length($name)) { print("Please try again\n"); }

} until (length($name));



Regular Expressions• Understands egrep-style EREs, plus:

\w, \W alphanumerics and _\d, \D digits\s, \S whitespace\b, \B word boundaries\t tab

• Special variables: $& means all text matched, $` (back quote) is text before match, $’ (single quote) text after

• Use \1 .. \9 within EREs, $1 .. $9 outside

if (/^this (red|blue|green) (bat|ball) is \1/){ ($color, $object) = ($1, $2); }



Regular ExpressionsSubstitute and translation operators are like sed:

s/alpha/beta/; # alpha --> beta in special variable $_

s/(.)\1/$1/g; # (blah) --> blah in special variable $_

y/A-Z/a-z/; # upper case --> lower case# in special variable $_

• Use =~ and !~ to match against variables

$var1 =~ s/pattern/replacement/; # substitute in $var1

if ($var =~ /pattern/) {...} # if $var has the pattern

if (<STDIN> =~ /^[xX]/) { ... } # if STDIN starts with X or x

if ($var !~ /pattern/) { ... } # if $var does not have a pattern



The Variable $_

• $_ is used a lot in Perl

• When variable is left out, $_ is used:

• Example:

foreach (@list) {... $_ ...} # points to “each”

s/good/bad/; # in whatever $_ is

if (/pattern/) {…} # if $_ matches “pattern”

if (!/pattern/) {…} # if $_ does not match “pattern”



I/O• Filehandles conventionally uppercase: STDIN, STDOUT, STDERR

• Mentioning a filehandle in angle brackets (<…>) reads next line:

• scalar context: returns line (with newline)

$line = <TEMP>;

• array context: returns all lines (with newlines)

@lines = <TEMP>;



I/O continued

• When used in a while construct, input lines are automatically assigned to the $_ variable.

• Typical usage: iterate over file one line at a time, using $_

while ( <> ) {next if /^#/; # continue - skip comments == if line starts with #last if /STOP/; # break - stop if a line with “STOP” reads/left/right/g; # global substitute: left --> rightprint; # print $_

}

• <> means all files supplied on command line (or STDIN if none) put together



Files• Opening a file

open(PWD, ”/etc/passwd”);open(TMP, ”>/tmp/foobar.$$”);open(LOG, ”>>logfile”);open(TOPIPE, ”| lpr”);open(FROMPIPE, ”ps –ef |”);open(PWD, ”/etc/passwd”) or die ”cannot open”;

• Printing:

print LOG ”This is a log entry\n”;printf LOG ”entry: %s\n”, $var

• awk influence

$, field separator (column delimiter)$/ record separator (line delimiter)



I/O Example# Read an array from a file$buffer = "";

open(FILE, "<binary.dat");read(FILE, $buffer, 20, 0);close(FILE);

# print the value of all array elements in hexadecimal format.

foreach (split(//, $buffer)) { # split into characters printf("%02x ", ord($_)); print "\n" if $_ eq "\n";}



Globbing

• Perl has globbing, similar to shell

• A string in angle brackets with metacharacters evaluates to a list of matching filenames

# change all *.c and *.h files to *.c.old and *.h.oldforeach $x ( <*.[ch]> ) {rename($x, “$x.old”);

}

chmod 711, <*.c>;



Subroutines• Defined with sub:

sub myfunc { ... }

• Subroutines calls are prefaced with &. Any of the three principal data types may be passed as parameters or used as a return value; e.g.,

&foo;

• Special variable $_ passed by default

• Parameters are received by the subroutines in the special array @_:

$_[0], $_[1], ...

• Local variables can be declared with my

• By default, $_ returned. Override with return statement



Subroutine Examples&foo; # call subroutine foo with $_

&foo(@list); # call foo passing an array$x = &foo(‘red’, 3, @arr); # foo returns a value that is assigned to x

@list = &foo; # foo returns a list

sub simple {my $sum; # local variableforeach $_ (@_) { # @_ is the list of parameters

$sum += $_;}

return $sum;}

$foo = ‘myroutine’;&$foo(@list); # call subroutine indirectly



Array Functions• push and pop functions:

– when arrays are used a stack of information, where new values are added to and removed from the right hand side of the list.

• Example:

push(@mylist, $newvalue); # like: @mylist = (@mylist, $newvalue);

$oldvalue = pop(@mylist); # removes last element of my list.



Array Functions (cont.)• shift and unshift functions:

– performs similar action to push and pop on the "left" side of a list.

• Example:

@fred = (5, 6, 7);unshift(@fred, $a) ; # like @fred = ($a, @fred);$x = shift(@fred); # x gets 5, @fred is now (6, 7)

• reverse function:– reverses the order of the elements of its argument, returning the resulting list

@a = (1, 2, 3);@b = reverse(@a); # means @b = (3, 2, 1);



Array Functions (cont.)• sort function:

– returns a sorted list in ascending ASCII order without changing original list

• grep function:– returns a new list consisting of all the elements which match the given expression

@lines = grep(!/^#/, @lines);



Array functions (cont.)•split

– breaks up a string into an array of new strings. You can split on arbitrary regular expressions:

@list = split(/[, \t]+/, $expr); # use any number of “,”, “ “ or “\t” to separate

while (<PASSWD>) { # use “:” to split lines in the PASWD file($login, $passwd, $uid, $gid, $gcos, $home, $shell) = split(/:/);

}

• The inverse of split is join

$line = join(‘:’, $login, $passwd, $uid, $gid, $gcos, $home, $shell);

• pattern “//” will split into single characters



Directory Access• Method 1:

• Open a pipe from /bin/ls:

open(FILES, “/bin/ls *.c |”);

• Method 2:

• The directory-reading routines are provided as built-ins and operate on directory handles. Supported routines are opendir, readdir, closedir, etc.

opendir(DIR, ".");@files = sort(grep(/pl$/, readdir(DIR))); # extract only those that end in plclosedir(DIR);

foreach (@files) { print("$_\n") unless -d; # print name unless the file is a directory}



Hash Table Functions• For manipulating associative (hash) arrays, the following functions are useful:

• keys: returns indexed array of keys

• values: returns indexed array of values

• each: returns indexed array of two-element arrays containing ($key,$value) pairs.

while (($key, $value) = each %array) { printf “%s is %s\n”, $key, $value;}

foreach $key (keys %array) { printf “%s is %s\n”, $key, $array{$key};}

print reverse sort values %array;



String functions• Several C string manipulation functions:

– crypt, index, rindex, length, substr, sprintf

• Adds others:– chop: removes the last character from a string (very useful for removing \n character)– chomp: removes last character only if \n– work with scalars or arrays

chop($line)

while (<STDIN>) {chomp;...

}

@stuff = (“hello\n”, “hi\n”, “ola\n”);chomp(@stuff);



Example Program#!/usr/bin/perl# Print out today’s yearday on stdout

($sec,$min,$hour,$day,$mon,$year,@rest) = gmtime();

@months = (31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31);

if ($year == 2000) { # A leap year $months[1] = 29;}$yearday = 0;for ($m=0; $m < $mon; $m++) { $yearday += $months[$m];}$yearday += $day;print $yearday . “\n”;



awk and sed Connection• a2p

– Translates an awk program to Perl

• s2p– Translates a sed script to Perl



Perl can get messy…

Write your own munitions…

#!/bin/perl -s-- -export-a-crypto-system-sig -RSA-3-lines-PERL$m=unpack(H.$w,$m."\0"x$w),$_=`echo "16do$w 2+4Oi0$d*-^1[d2%Sa2/d0<X+d*La1=z\U$n%0]SX$k"[$m*]\EszlXx++p|dc`,s/^.|\W//g,printpack('H*',$_)while read(STDIN,$m,($w=2*$d-1+length$n&~1)/2)



Packages (Modules)• A collection of functions

– Usually stored in a file called MyModule.pm

• Each has its own namespace– Access with: $MyModule::Variable– Default package is $main

• To use a package: use MyModule;

• To create a module:– Start off with: package MyModule;– Definitions of subroutines and variables– Export routines/variables to global namespace– Indicate success with line:

1; #last statement in file

• Many available packages:– e.g., CGI



Perl as a CGI scripting language• CGI - Common Gateway Interface

– allows for embedding actions on Web pages

– Java Servlet - same idea, but needs a Java Application Server (J2EE)– Microsoft has .Net

Web Browser Web Browser

html

Web Browser Web Server

cgi CGI Engine

html

e.g., Perl program e.g., Perl interpreter

Simple file serving

Similarly, .txt, .jpg, .pdf, etc.



cgi.pm• Perl module for CGI parsing (Perl 5 and newer)

– Also includes utility functions for generating HTML, debugging, etc.

$ cat birthday.cgi#!/usr/bin/perluse CGI;$query = CGI::new();$bday = $query->param("birthday");print "Content-type: text/html\n\n";print "Your birthday is $bday <br>\n";$ chmod 755 birthday.cgi$ birthday.cgi birthday=11/5/02 # pass the parametersContent-type: text/html

Your birthday is 11/5/02



CGI Script: Example



Part 1: HTML Form<html><center><H1>Anonymous Comment Submission</H1></center>Please enter your comment below which willbe sent anonymously to me.<p><form action=cgi-bin/comment.cgi method=post><textarea name=comment rows=20 cols=80></textarea><input type=submit value="Submit Comment"></form></html>



Part 2: CGI Script (Perl)#!/usr/bin/perl

use CGI;$query = new CGI;

$comment = $query->param('comment');$recipient = '[email protected]';$sendmail = '/usr/sbin/sendmail';

open(MAIL, "|$sendmail -oi -t") or die "Can't open pipe to $sendmail: $!\n";print MAIL "To: $recipient\n";print MAIL "Subject: Sample Web Form Submission\n\n";print MAIL "$mail_body";close(MAIL) or die "Can't close pipe to $sendmail: $!\n";



Part 2: CGI Script (Perl)

print "Content-type: text/html\n\n";print <<"EOF"; # print everything literally until the text<HTML><HEAD><TITLE>Thank you</TITLE></HEAD><BODY><H1>You submitted the following comment:</H1><pre>EOF # end of the first printprint $comment . "\n";print <<"EOF";</pre><H1>Thank you</H1><P>Thank you for your form submission.</BODY></HTML>EOF



CGI environmentLogin to HP servers and do the following:

$ mkdir public_html$ cd public_html$ vi page.html # enter the HTML file$ chmod 644 page.html$ mkdir cgi-bin$ cd cgi-bin$ vi script.cgi # enter the CGI script (Perl program)$ chmod 755 script.cgi

Then open a browser and go to http://www.csun.edu/~yourname/page.html



Another Example#!/usr/bin/perl# Dump parameters and environment variables

use CGI;

$query = CGI::new;print &CGI::header;

print "<H1> Date </H1>\n";print "<pre>\n";print `date\n`;print "</pre>\n";

print "<H1> Form Variables </H1>\n";print "<pre>\n";foreach $p (sort(($query->param))) { print "$p = " . $query->param($p) . "\n";}print "</pre>\n";

print "<H1> Environment </H1>\n";print "<pre>\n";foreach $p (sort((keys ENV))) { print "$p=" . $ENV{$p} . "\n";}print "</pre>\n";



Another Example with Database Access<html><head><title>User Database Access Test - perl</title></head><body><h1>User Database Access Test - perl</h1><p><form action="http://www.some.com/userData.cgi" method=post>A simple example to find information about a user data.<br>Enter your user ID name<input type=text name=“ID”><br><input type=submit value="Search database"></form><p></body></html>



Another Example with Database Access#!/usr/local/bin/perluse CGI;# DBI is a module with a database connectoruse DBI;

$query = new CGI;# a debugging option that sends error messages to the browser rather# than log fileuse CGI::Carp qw(fatalsToBrowser);# print page headerprint "Content-type: text/html\n\n";print "<html><head><title>Location query</title></head>";print "<body><h1>Location query</h1><p>";# connect to the database “userDatabase” with ID “demo” and password “”$dbConnector = DBI->connect("dbi:mysql:userDatabase","demo","")

or die("Couldn't connect");# import names from the query page into a namespace ‘MySpace’$query->import_names(’MySpace');# prepare a database query$sqlTable = $dbConnector->prepare("select * from placeDatabase where feature = ?")

or die("Couldn't prepare");



Another Example with Database Access# execute the query replacing ‘?’ with $MySpace::ID$sqlTable->execute($MySpace::ID);# are there any rows in the table?if($sqlTable->rows == 0){ print "No information for " . $MySpace::ID;}else{ print "<table border=2>\n";# get the row and put it into an associative array (a hash) while( $rowHash = $sqlTable->fetchrow_hashref() ) { print "<tr>"; print "<td>" . $rowHash->{”name”}; print "<td>" . $rowHash->{”address"}; print "<td>" . $rowHash- >{”telephone"}; print "<td>" . $rowHash- >{”email"}; print "\n"; } print "</table>\n";}print "</body></html>\n";# disconnect from the database$dbConnector->disconnect;

Ch. 2. UNIX for Non-Programmers

Perl Challenge



Homework/Project• Read the CGI/Perl tutorials (see my links) - start with the “beginners”

• Implement the following Web-based pizza ordering system:

• You should have forms for:– delivery address– some selection for pizza (ingredients, style, etc.)– credit card information and– email address for confirmation.

• You do not need to store the data.

• You do not need to verify and charge credit card.

• The data collected from the form should be sent to your email address.

• A confirmation with order details should be displayed on the new page.

• You’ve got 3 weeks! I need the link to try out your program and your HTML file and CGI script.

introduction to perl lecturer: prof. andrzej (aj) bieszczad email: [email protected] phone:...

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