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The no Function in Perl

Designing and Using a Perl Module Part 3

Foreword: In this part of the series, I talk about the no predefined function in Perl; this function is applied in library use.

By: Chrysanthus Date Published: 2 Apr 2016

Introduction

This is part 3 of my series, Designing and Using a Perl Module. In this part of the series, I talk about the no predefined function in Perl; this function is applied in library use. You should have read the previous parts of the series before coming here, as this is a continuation.

The Function
The no function does not really have a precise application. Its use depends on the context.

Used with Many Pragmas
It can be used to forbid the use of a pragma. For example, instead of typing at the top,

    use strict;

you can type at the top,

    no strict;

In this case, for the rest of the program, there is no strictness and you can declare a variable just like that, without using the my or our operator. However, this can be countermand in an inner block. That is, if at the beginning of an inner block, you type,

    use strict;

within that inner block, strictness applies and you have to declare a variable preceded by the my or our operator, in the block. Outside the block, strictness does not apply.

Another situation is with,

use VERSION

e.g.

    use 5.006;

typed at the top of the current program. This means the Perl interpreter version should not be greater than 5.006. Now, you may not know the version of the Perl interpreter (or you may have some other interest); you can type at the top,

    no VERSION;

This means that the version of the Perl interpreter may be greater than the specified one. So you would have something like:

    use 5.006;
    no VERSION;

where the first line indicates the version.

There are other cases of the use of the no operator and the meaning depends on the context.

End of Tutorial and end of Series
This is the end of the tutorial and the end of the series. I hope you appreciated the series.

Chrys

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