Perl: Lecture 3

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Perl Lecture 3

• Organization Modern Perl

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File Upload using CGI.pm

• ltFORM ENCTYPE"multipart/form-data"
• ACTION"/cgi-bin/upload.pl" METHOD"POST"gt
• Please select a file to upload ltBRgt
• ltINPUT TYPE"FILE" NAME"file"gt ltpgt
• ltINPUT TYPE"submit"gt
• lt/FORMgt

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File Upload using CGI.pm (2)

• use CGI
• file param('file')
• filem/.(\\\/)(.)/ strip the remote path
  and keep the filename
• name 2
• open(LOCAL, "gtname")
• while(ltfilegt)
• print LOCAL _
• print header()
• print "file has been successfully uploaded...
  thank you.\n"

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CPAN

• Comprehensive Perl Archive Network
• http//search.cpan.org
• Contains libraries for just about anything
• Installing libraries
• CPAN module (Perl general)
• PPM (Windows, Activestate)

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PPM

• Perl Package Manager
• Command PPM
• Interactive shell
• install TimeHiRes
• quit
• perldoc TimeHiRes

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Example Module MailPOP3Client

• Gives functionality of a POP3 client to a script
• new (USERgtuser, PASSWORDgtpassword,
  HOSTgthost)
• New connection
• head(message_number)
• body(message_number)
• delete(message_number)
• Count
• Get number of messages
• ListArray
• Get list of sizes of messages

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Invoking other processes

• TMTOWTDI
• exec
• system
• open
• backtick

exec dir
system dir
open DIR, dir while (ltDIRgt) print
_at_entries dir print _at_entries
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Security Taint mode

• Problem Data input by user used to build command
  line
• perl -T command line switch
• External data is marked as tainted, unsafe
  operations are impossible
• Laundering data by e.g regular expressions

if (data /(\w)/) data1 else
die
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Array Processing (1)

• push ARRAY, LIST
• Treats ARRAY as a stack, and pushes the values of
  LIST onto the end of ARRAY
• pop ARRAY
• Pops and returns the last value of the array,
  shortening the array by one element

new
new
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Array Processing (2)

• unshift ARRAY, LIST
• Prepends list to the front of the array.
• shift ARRAY
• Shifts the first value of the array off and
  returns it, shortening the array by 1

new
new
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Array Processing (3)

• splice ARRAY, OFFSET ,LENGTH ,LIST
• removes and returns LENGTH items from ARRAY
  starting at OFFSET and replaces them with LIST
• grep EXPR, LIST
• returns list elements for which the EXPR
  evaluated as true
• sort LIST
• sorts and returns LIST

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Hash functions

• delete EXPR
• deletes an element of the hash
• each HASH
• Return next ordered PAIR of key, value or key
  only if in scalar context
• exists EXPR
• True if hash has an element with key EXPR
• keys HASH
• Return list of keys of a hash
• Values HASH
• Returns list of values in hash

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References

• Variable holding address of other variable
• Target may be scalar, hash, array ...
• Automatic memory management
• No malloc / free
• Automatic garbage collection

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References (1)

• \ operator
• Analogue to Cs operator
• scalarref \scalar
• arrayref \_at_ARGV
• Anonymous references
• arrayref 1,2, a, b, c
• hashref A gt 1, B gt 2

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References (2)

• dereferencing operator
• scalar text
• scalarref \scalar
• scalar2 scalarref
• print _at_arrayref
• arrayref0 January

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Reference (3)

• -gt dereference operator
• arrayref0 January
• arrayref-gt0 January
• hashrefkey February
• hashref-gtkey February

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Manipulating Lists of Lists

• _at_twodim ( a1, a2 ,
• b1, b2, b3 ,
• c1, c2, c3 )
• print twodim22
• ref_to_twodim a1, a2 ,
• b1, b2, b3 ,
• c1, c2, c3

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References Overview Table

• Setting Using
• (reference) (dereference)
• Scalar r \s r
• Array ra \_at_a _at_ra, ra2
• Hash rh \h rh,
• rhkey

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Nested Data Structures

• h1 ( "user" gt "u1", "password" gt "p1" )
• h2 ( "user" gt "u2", "password" gt "p2" )
• _at_datastr ( \h1, "a1", "b1" ,
• \h2, "a2", "b2" )
• foreach entry (_at_datastr)
• print entry0user . "" .
  entry0password . "\n"
• print entry1 . "\n" . entry2 . "\n"

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Packages / Perl Modules (1)

• A package is a namespace
• Package usually one file
• Packagename.pm
• To use a module
• use module
• Import functions and variables

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Packages / Perl Modules (2)

• Always inside a package, default main
• package directive
• Current block gets a new namespace
• Specifying namespaces for identifiers -
• PackageVariable
• BEGIN / END subroutines

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Perl Plain Old Documentation

• Paragraph styles
• Verbatim
• Indented
• Command
• head1, head2 Headings
• over, back, item List
• cut End of POD
• Ordinary

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Finish