Perl: Lecture 2

1
Perl Lecture 2

• Advanced RE CGI

2
Regular Expressions 2
3
Advanced Pattern Matching

• Anchor Metacharacters
• Beginning of String
• End of String

"housekeeper" /keeper/ matches
"housekeeper" /keeper/ no match
"housekeeper" /keeper/ matches
"housekeeper\n" /keeper/ matches
"housekeeper" /housekeeper/ matches
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Character classes

• notation
• - range of characters
• negated

/bcat/ matches 'bat', 'cat' "abc"
/cab/ matches 'a' /\cdef/ matches
'def' or 'cdef'
/item0-9/ matches 'item0' or ... or
'item9' /0-9a-fA-F/ matches a hexadecimal
digit
/0-9/ matches a non-numeric character
5
Common Character Classes

• \d digit 0-9
• \s whitespace \ \t\r\n\f
• \w word character 0-9a-zA-Z_
• \D negated \d 0-9
• \S negated \s \s
• \W negated \w \w
• '.' any character but ''\n'
• \b word boundary \w\W or \W\w

6
Alternation Grouping

• alternation operator
• ( ) grouping
• m//i modifier
• Case-insensitive match

"cats and dogs" /dogcatbird/ matches
"cat"
/house(catkeeper)/ "20" /(1920)\d\d/
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Extracting Matches

• Grouped patterns can be extracted

time /(\d\d)(\d\d)(\d\d)/ hours 1
minutes 2 seconds 3 (hours,
minutes, second) (time
/(\d\d)(\d\d)(\d\d)/)
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Matching repetitions

• Quantifier Metacharacters
• ? 0 or 1 times
• 0 or more times
• 1 or more times
• n,m at least n, at most m times
• n, at least n times
• n exactly n times

/\w/ matches a word year /\d4\d2/
2 or 4 digit years
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Search and Replace

• s/regex/replacement/ Syntax
• replaces only one occurence
• s///g modifier replaces all occurences

x "Time to feed the cat!" x
s/cat/dog/ y s/'(.)'/1/
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RE functions

• quotemeta EXPR
• escapes all RE metacharacters
• split /PATTERN/, EXPR
• splits a String at a delimiter specified by
  PATTERN
• pos SCALAR
• Returns offset of last m//g occurence

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Time functions

• time
• Returns number of seconds since jan 1, 1970
• localtime
• Convert time to human-readable format
• (sec,min,hour,mday,mon,year,wday,yday,is
  dst) localtime(time)
• gmtime
• Do the same on the basis of GMT

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CGI
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What is CGI?

• Common Gateway Interface
• Not a programming language
• Method for the web server for the invocation of a
  program on a users request
• Method of exchanging data between a user, a web
  server and the program

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CGI Functionality

• CGI Program invoked when its URL is requested
• Parameters / Data Included in the request

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Setting up the web server for Perl CGI

• Example Microsoft Windows, Apache HTTPD
• HTTPD is preconfigured for scripts
• http//host/cgi-bin
• ! required (e.g. !C\perl\bin\perl)
• Possibly delete windows file type association

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CGI Data Exchange overview
Web Server
Perl Script
Request GET / POST
Response
User
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Simple CGI program

• !/usr/bin/perl
• print Content-type text/html\n\n
• print lthtmlgtltheadgtlt/headgtltbodygt
• print lth1gtThis is CGIlt/h1gt
• print lt/bodygtlt/htmlgt

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CGI Environment Variables

• HTTP_ACCEPT"/"
• HTTP_ACCEPT_ENCODING"gzip, deflate"
• HTTP_ACCEPT_LANGUAGE"en-us"
• HTTP_CONNECTION"Keep-Alive"
• HTTP_HOST"localhost"
• HTTP_USER_AGENT"Mozilla/4.0 (compatible MSIE
  6.0 Windows NT 5.0)"
• QUERY_STRING""
• REMOTE_ADDR"127.0.0.1"
• REMOTE_PORT"3039"
• REQUEST_METHOD"GET"
• REQUEST_URI"/cgi-bin/printenv.pl"
• SCRIPT_NAME"/cgi-bin/printenv.pl"
• SERVER_ADDR"127.0.0.1"
• SERVER_ADMIN"trace_at_gmx.net"
• SERVER_NAME"ba35002"
• SERVER_PORT"80"
• SERVER_PROTOCOL"HTTP/1.1"
• SERVER_SIGNATURE"ltADDRESSgtApache/1.3.27 Server
  at ba35002 Port 80lt/ADDRESSgt\n"
• SERVER_SOFTWARE"Apache/1.3.27 (Win32) PHP/4.2.3"

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Generating the response

• Own result
• Content-type text/html
• print "Content-type mime_type\n\n"
• Redirection
• Location http//www.domain.com/newpage
• print "Location url\n\n"

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Getting client data to the server

• Usually from an HTML form
• Two methods defined in HTTP
• GET
• Data in request URL
• Accessable by CGI script using QUERY_STRING env
  var
• POST
• Data after request
• Accessable STDIN and CONTENT_LENGTH env var
• Both methods use URL-encoding
• Fields separated by , values after sign
• Space -gt
• Special characters -gt xx

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Where is the data? HTML Forms (1)

• ltform actionURL methodget/postgt
• lt/formgt
• ltinput typesubmit valuelabel /gt
• ltinput typereset valuelabel /gt
• ltinput namename typepassword /gt

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Where is the data? HTML Forms (2)

• lttextarea namename /gt
• ltselect nametop5 multiplegt
• ltoption valuevaluegtLabellt/optiongt
• lt/selectgt
• ltinput typeradio namename valuevalue /gt
  Label
• ltinput typecheckbox namename valuevalue
  /gt Label
• ltinput typehidden namename valuevalue /gt

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GET / POST examples

• GET example
• POST example

GET /cgi-bin/script.pl?inhellotherebuttonSend
HTTP/1.0
POST /cgi-bin/script.pl HTTP/1.0 Content-type
application/x-www-form-urlencoded Content-length
26 inhellotherebuttonSend
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Tasks to work with data

• Find out if GET or POST is used
• Split into single fields
• URL-decode
• Send HTTP header w/MIME-type data
• Used for nearly every CGI script, so already
  build into Perl!

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CGI.pm example
use CGI qw(standard) print header() _at_namespa
ram() foreach name (_at_names) my
_at_valueparam(name) print name -gt
_at_valueltbrgt\n"
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Error 500?

• Internal Server Error
• Script behaved incorrectly
• See Web Server Log for more details
• apache\logs\error.log