Scalar Value Constructions
Perl Data Types – Part 3
Foreword: In this part of the series, I talk about scalar value constructions.
By: Chrysanthus Date Published: 22 May 2015
An integer is a whole number. A number can be an integer, as the following statement shows:
$num = 54;
A number with a decimal point is a floating-point number. A number in Perl can be a float as the following statement shows:
$num = 23.48;
In Perl, if a number is long, you do not use commas to group the digits in threes; you use but the underscore, as in the following statement:
my $num = 4_294_967_296;
This is the number, 4294967296, written on paper as 4,294,967,296, but written in Perl as 4_294_967_296 or 4294967296 (without any separation).
You can write a number in Perl in what is known as Perl’s Exponential Form. The number 256.39 can be written in Perl’s exponential form as,
To code a number this way, you begin with a digit. This is followed by a decimal point. After that you have the rest of the digits without any other decimal point. Then you have the letter, E. This is followed by + or - .You type + if the decimal point has to be moved to the right to reach its original position. You type – if the decimal point has to be moved to the left to reach its original position. Then you type a number for the number of digits the decimal point has to be carried over to reach its original position.
In Perl, a normal string literal is text in double quotes or single quotes. For a double quoted string, a variable in the string is substituted by its value, and an escape sequence in the string takes its effect. For a single quoted string, a variable is not substituted by its value and an escape sequence does not take effect, except for \' and \\ .
So for the code segment,
my $quantity = 50;
my $str = "I have $quantity of them.\nYou have nothing.";
The string would be printed as:
I have 50 of them.
You have nothing.
At the output, $quantity has been replaced by 50 and the \n has had its effect creating a new line. Neither $quantity nor \n could have caused any change if the string was within single quotes.
Try the following code where the string is delimited by single quotes:
my $quantity = 50;
my $str = 'I have $quantity of them.\nThe \\ and \' take effect';
The output is:
I have $quantity of them.\nThe \ and ' take effect
Since the string is within single quotes, $quantity has not been expanded (replaced by its value); \n has not had its effect. The single quote exceptions of \\ and \' have had their effects: \\ is the escape sequence for \ and \ alone has been displayed; \' is the escape sequence for ' and only ' has been displayed.
Special literals are: __FILE__, __LINE__, __PACKAGE__, __SUB__, __END__ and __DATA__ . Here I will only talk about __FILE__ and __LINE__ . I will talk about the rest later as we go along in the course. Each of these literals has double underscores, __.
__FILE__ represents the current filename. I tried
print __FILE__ ;
in my computer and I had
where C:\ is the directory path and sample.pl is the name of the file.
__LINE__ represents the current line number in the file. I tried
print __LINE__ ;
in my computer and I had
because the print statement was typed at line 10 in the file, counting from the top. Note: line counting begins from 1 and not zero.
A reference is the equivalent of the starting address of an entity in memory. Try the following code:
my $myVar = "We are the world.";
my $item = \$myVar;
print $item, "\n";
In memory, you have the entity, "We are the world.", which is identified by the variable, $myVar. To obtain a reference to this scalar entity, precede the $myVar variable with \ . The return value of that is held by the scalar variable, $item in the code. This is not holding a normal value (string or number); it is holding a reference, which is a kind of scalar. In my computer the printing of $item gives,
which is of the starting address of the string entity.
A bareword can be considered as a stray word in code, not preceded by $ or @ or % or &. Its presence is an error.
That is it for this part of the series. We stop here and continue in the next part.
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Commonly Used Perl Predefined Functions
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Handling Strings in Perl
Using Perl Arrays
Using Perl Hashes
Perl Multi-Dimensional Array
Date and Time in Perl
Namespace in Perl
Perl Eval Function
Writing a Perl Command Line Tool
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Miscellaneous Features in Perl
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