5 Useful Perl 5.10 Features – Say, State, ~~, Defined OR

Even though Perl 5.10 is an old release, there are few things that was introduced in Perl 5.10, which you might find it useful.

In the future article of this series, we’ll be covering new features of Perl 5.14

These are the 5 new Perl 5.10 features that you might find helpful.

1. Say it instead of Print

The major difference between say and print is, say prints a newline at the end by default. So, when you use “say”, you don’t need to give the “\n” at the end.
Both of the following does the exact same thing:

print "Hello World!\n";
say "Hello World!";

So most of the programmers would find it handy as they print newline at the end of message mostly.

2. Named Captures in Regex

Parenthesis can be used to do named capturing in this format: (?<name>REGEX)

The text captured by the regular expression can be accessed by its name as key in the hash named +

$+{name}

The same way to access the named capture in the substitute you can use the following method – which is similar to \1 or \2 in capturing parenthesis.

\g{name}

Example: The following code snippet demonstrates named capture use after match and during match.

use v5.10;

$_ = 'bob23';

if ( /(?<username>\D+)(?<age>\d+)/ ) {
	say "User $+{username}'s age is $+{age}";
}

$userdetails = 'Username:sathiya, password:sathiya';

if ( $userdetails =~ /Username:(?<username>.*), password:(\g{username})/ )  {
	say "Username and password are identical for $+{username}";
}

• In the first pattern match, username and age are captured and used from + hash after match.
• In the second pattern match, username is captured and used during match with \g.

Note: Even if you have different names for capture you wont have it after next match. Remember to store the named capture to other variable because the next match will reset this hash %+.

3. State – Persistent Variable across Function Calls

When you want a variable to hold data across function calls in a function, a simple way earlier is to use global variables but that would allow manipulation of that variable from anywhere.

In perl 5.10 ‘state’ would be a perfect solution for that.

Example: Counter variable to maintain how many times a function has been accessed.

use v5.10;

sub func {
    state $accessed = 0;
    say 'function accessed ', ++$accessed , ' times';
}

&func();
&func();
&func();

This prints the following output when executed:

function accessed 1 times
function accessed 2 times
function accessed 3 times

The variable $accessed is initialized only once.

4. Defined OR Operator ( // )

Difference between OR operator and Defined OR operator

$result = $a || $b;
$result = $a // $b;

• OR Operator: $b will be stored in $result if $a has value 0 or empty.
• Defined OR Operator: $b will be stored in $result only if $a is not defined. But if $a has 0 or empty, then $a value will be stored into $result.

5. Smart Match Operator ( ~~ )

It can act as == or eq according to the data on both sides.

Example:

if ( 4 ~~ "4.0" )  {
  print 'matched'
} else {
  print 'not matched'
}

This will print ‘matched’. But if you use -eq operator instead it will try to do a string comparison and print ‘not matched’.

Smart match is more smarter, as it can compare a string against a list, hash with hash, etc.