How do I create a switch or case statement?

This is explained in more depth in the the perlsyn manpage. Briefly, there's no official case statement, because of the variety of tests possible in Perl (numeric comparison, string comparison, glob comparison, regex matching, overloaded comparisons, ...). Larry couldn't decide how best to do this, so he left it out, even though it's been on the wish list since perl1.

The general answer is to write a construct like this:

for ($variable_to_test) {   
    if    (/pat1/)  { }     # do something 
    elsif (/pat2/)  { }     # do something else
    elsif (/pat3/)  { }     # do something else
    else            { }     # default
}
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Here's a simple example of a switch based on pattern matching, this time lined up in a way to make it look more like a switch statement. We'll do a multi-way conditional based on the type of reference stored in $whatchamacallit:

SWITCH: for (ref $whatchamacallit) {
    
    /^$/            && die "not a reference";
    
    /SCALAR/        && do { 
                            print_scalar($$ref);
                            last SWITCH;
                    };
    
    /ARRAY/         && do { 
                            print_array(@$ref);
                            last SWITCH;
                    };
    
    /HASH/          && do { 
                            print_hash(%$ref);
                            last SWITCH;
                    };
    
    /CODE/          && do { 
                            warn "can't print function ref";
                            last SWITCH;
                    };
    
    # DEFAULT
    
    warn "User defined type skipped";

}
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See "perlsyn/"Basic BLOCKs and Switch Statements"" for many other examples in this style.

Sometimes you should change the positions of the constant and the variable. For example, let's say you wanted to test which of many answers you were given, but in a caseinsensitive way that also allows abbreviations. You can use the following technique if the strings all start with different characters or if you want to arrange the matches so that one takes precedence over another, as ""SEND"" has precedence over ""STOP"" here:

chomp($answer = <>);
if    ("SEND"  =~ /^\Q$answer/i) { print "Action is send\n"  }
elsif ("STOP"  =~ /^\Q$answer/i) { print "Action is stop\n"  }
elsif ("ABORT" =~ /^\Q$answer/i) { print "Action is abort\n" }
elsif ("LIST"  =~ /^\Q$answer/i) { print "Action is list\n"  }
elsif ("EDIT"  =~ /^\Q$answer/i) { print "Action is edit\n"  }
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A totally different approach is to create a hash of function references.

my %commands = (
    "happy" => \&joy,
    "sad",  => \&sullen,
    "done"  => sub { die "See ya!" },
    "mad"   => \&angry,
);

print "How are you? ";
chomp($string = <STDIN>);
if ($commands{$string}) {
    $commands{$string}->();
} else {
    print "No such command: $string\n";
}
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You'll note that the methods noted in above post, while supporting the general use of switch, do not support default fall-through like C does. To be fair, this is one of the most contreversial features in C (culminating in Duff's Device), but arguments over potential abuse of a feature never stopped Perl before. So it's no small irony that even Java supports a more C-ish switch statment then Perl does.

You might like to look at the thread at Simple Switch statement for a recent discussion of an interesting variation on the theme of self-implemented switch statements. This, in a slightly modifed as shown at Re: Simple Switch statement, is now my current favorite variation.