CMPS 335 Advanced Web Publishing Perl and CGI Programming


Functions

Individual statements are often gouped into logical units called procedures.  There are two major types of procedures used in Perl: functions and subroutines.  In general, system-defined procedures are called functions and user-defined procedures are subroutines.   A function may have operands called arguments or parameters.  Arguments are usually enclosed in parentheses and are separated by commas if there are more than one.  A function returns a value as shown in the following examples:
a. shift(@array); If @array contains (a,b,c), the result of shift(@array) is (b,c) and the return value is a.
print statememnt; The return value of any print statement is 1 if it is successful. ; Some important functions are listed below.

Array Functions 
   Function   Syntax                      Description
  -------------------------------------------------------------
   pop        $var = pop(@arrayname);
       Returns the last value of the array
   push       push(@arrayname, element); 
       Adds the element to the end of the array
   sort       sort(@arrayname);
       Sorts the values of the array alphabetically
   reverse    reverse(@arrayname);
       Reverses the values of the array alphabetically  
   scalar     $var = scalar(@arrayname); 
       Returns the size of the array

   Examples 
   @colors = ("red","blue","green");
   print "@colors\n";
   $size = $#colors + 1;     # array size using $#arrayName+1
   print "There are $size colors\n";
   $size = scalar(@colors);  # using scalar function
   print "There are $size colors\n";
   @reversedColors = reverse(@colors);
   print "@reversedColors\n";
   $color = pop(@colors);
   print "$color\n";
   print "@colors\n";
   push(@colors,"black");
   print "@colors\n";
   @sortedColors = sort(@colors);
   print "@sortedColors\n";

   Output
   red blue green
   There are 3 colors
   There are 3 colors
   green blue red
   green
   red blue
   red blue black
   black blue red

Hash Functions 
   Function   Syntax                      Description
  -------------------------------------------------------------
   delete     delete $hashName{$key}
       Deletes the specified key/value pair and returns    
       the deleted value
   exists     exists $hashName{$key}
       Returns true if the specified key exists in the hash
   keys       keys %hashName or keys(%hashName)
       Returns a list of keys for that hash
   values     values %hashName or  values(%hashName)
       Returns a list of values for that hash   
   scalar     scalar %hashName
       Returns true if the hash has any element defined  

   Examples
   %personal = ("age"=>26,"name"=>"Janice","address"=>"427 Main");
   @values = values(%personal);  # Getting all values
   @keys = keys(%personal);      # Getting all keys
   print "Keys are: @keys \n";
   print "Values are: @values \n";

   Output
   Keys are: name age address
   Values are: Janice 26 427 Main

String Functions 
   Function   Syntax                      Description
  -------------------------------------------------------------
   chomp      variable = chomp($scalar);
       Removes a newline character from the end of a string
   chr        variable = chr(number);
       Translates a number into a character
   length     variable = length(expression);
       Returns the number of characters in a string
   m//        $searchedString =~ m/pattern/;
       Returns true value if the pattern is matched in the $string
   pack       pack(TEMPLATE, inputList);
       Takes a character code and translates a corresponding character
       to the format specified
   split      variable = split(/pattern/,expression);
       Separates the expression into parts
   s///       $searchedString =~ s/oldPattern/newPattern/;
       Replaces one string for another string
   sbstr      variable = substr(expression,startingPoint,length);
       Returns or modifies a substring
   tr///        $string =~ tr/searchString/replacementString/;
       Translates every character in search string to its corresponding 
       character in replacement string
   uc         variable = uc(expression);
       Changes all the characters in the expression to uppercase


The time and localtime Functions

The time function returns a 4-byte integer denoting billions of seconds since January 1, 1970.  The localtime(time) function returns the local time parts in the specific order as shown below:    sec,min,hour,dayOfMonth,month,weekday,year,dayLightSaving
where
   Example:
  [jhu@cs ~/public_html/cgi-bin]$ cat perltime.cgi 
  #!/usr/bin/perl
  print "Content-type:text/html\n\n";
  ($sec,$min,$hour,$dayOfMonth,$month,$weekday,$year,$dayLightStandardTime)
     = localtime(time);
  $month = $month+1;
  $year = $year + 2000;
  $dayOfMonth = $dayOfMonth +1;
  print "$month/$dayOfMonth/$year\n";
  # End perltime.cgi 
 
  [jhu@cs cgi-bin]$ perl perltime.cgi
  10/16/2001

The tr/// Function

The translate function is a general purpose character-translation function.  It exchanges each occurrence of a character in the search string with its corresponding character in the replacement string.  The basic syntax of the translate function is: 
   Examples
   $string1 = "Hello.  My name is David.";
   $string1 =~ s/David/Kenneth/;
   print "$string1\n";

   $string2 = "Southeastern+Louisiana+University";
   $string2 =~ tr/a-z/A-Z/;
   print "$string2\n";

   $string2 =~ tr/+/ /;
   print "$string2\n";

   $s1 = "a,b,c.d.e";
   $s1 =~ tr/\,\./-/;
   print "$s1 \n";
   $s2 = "a,b,c.d.e";
   $s2 =~ tr/,./-/;
   print "$s2 \n";
   $s3 = "a,b,c.d.e";
   $s3 =~ tr/,./+-/;
   print "$s3 \n";
   $s4 = "a,b,c.d.e";
   $s4 =~ tr/,./ /;
   print "$s4 \n";
   $s5 = "a,b,c.d.e";
   $s5 =~ tr/,.//;
   print "$s5 \n";
   
   (Output)
   Hello.  My name is Kenneth.
   SOUTHEASTERN+LOUISIANA+UNIVERSITY
   SOUTHEASTERN LOUISIANA UNIVERSITY   
   a-b-c-d-e
   a-b-c-d-e
   a+b+c-d-e
   a b c d e
   a,b,c.d.e

The functions m//, split, and s/// are three primary functions that use regular expressions.  They provide powerful string manipulation capabilities and are discussed in the chapter on Regular Expressions.

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