Perl Example #4
Using Simple Perl Functions

About the Program

The next function is "pop" which chops off the highest element from an array, and returns that value. Naturally, there is a push function, but it is not demonstrated. The sort command is shown, however.

The final part of the program shows how to implement the equivalent of a "case statement", since there is no "switch" command in Perl as there is in C or C++ languages. It uses the power of matching and regular expressions in order to achieve the same result.

#!/usr/bin/perl
# Using Simple Perl Functions

print "Enter pattern:";
$pattern = <STDIN>;

# Scan through the passwd file. Create an array of lines with search pattern

@people = `cat /etc/passwd | grep $pattern`;
print @people, "\n";

# This section manipulates the strings grabbed from the passwd file 

$j=0;
for ($i = 0; $i<= $#people; $i++)
  {$_ = $people[$i]; 

   # Use "split" to break the string into separate elements between colons

   @passwd_data[0..6]= split(":");  # Using double quotes for the delimiter 
 
   # This field contains the full name of the user

   print $passwd_data[4];

   print "\n";

   # Use "split" to break apart first and last names
 
   @temp = split(/ /, $passwd_data[4]);  # Use the slash for a delimiter
  
   # Use the function "pop" to pull off the last name
   $lastnames[$j] = pop(@temp);


   #print last name first, then what's left in @temp (first name)

   print $lastnames[$j],", ", @temp , "\n\n"; 

   $j++;
  }

$,="\n ";  # Change the print separator to a carriage return

# Use the "sort" function to sort the array
print "Sorted by last name: ",sort @lastnames;
print "\n";

$,="";    # Reset the print separator to null


# Emulating the "switch" statement

print "Do they like Perl?\n";

while (<>)  # Infinite loop requesting keyboard response
  {
    $answer = "I don't understand. Type 'Q' to quit";
   
    REPLY:  # Skip other statements at "last REPLY".  Exit loop at "goto".
     {
       # Beginning "y" followed by possibly "es" at end, and ignore case
       /^y(es)?$/i  && do { $answer= "Perl is Kewl!"; last REPLY; };

       # Beginning "n" followed by possible "o", ignore case
       /^no?$/i  &&  do { $answer = "What a shame..."; last REPLY; };

       # The exact word "maybe", but ignore case
       /^maybe$/i  &&  do { $answer = "Let's learn more."; last REPLY; };
 
       # Beginning "q", or the word "quit", ignoring case.  Jump out of "while"
       /^q(uit)?/i  &&  do { $answer = "QUIT"; print "Thanks!\n";goto EXIT; };
     }

     print $answer, "\n";
     print "But, do they like Perl?\n";

  }

EXIT:
print "Going on....\n";

The actual program: ex4.pl

The output: ex4.out