Perl how to check if array is still empty?

Question

This should be simple hopefully. I initialize an empty array, do a grep and place the results (if any) in it, and then check if it's empty. Like so:

my @match = ();
@match = grep /$pattern/, @someOtherArray;
if (#match is empty#) {
    #do something!
}

What's the standard way of doing this?

You can define and initialize @match on the same line - my @match = grep etc. — Bill Ruppert
– Bill Ruppert, Commented Oct 5, 2012 at 18:40

mob · Accepted Answer · 2012-10-05 18:32:00Z

85

You will see all of these idioms used to test whether an array is empty.

if (!@match)
if (@match == 0)
if (scalar @match == 0)

In scalar context, an array is evaluated as the number of elements it contains.

answered Oct 5, 2012 at 18:32

mob

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3 Comments

friedo Over a year ago

Don't forget unless ( @match )

mob Over a year ago

Do forget unless (@match). (but that's just, like, my opinion, man)

veeTrain Over a year ago

Are the converses to these also true? If you wanted to control behavior for when at least one element was present, I'm assuming it would be if (@match) and if (@match != 0) but I thought I ought to check

brian d foy · Accepted Answer · 2021-12-18 05:22:46Z

-2

If you are using an arrayref instead of an array say for e.g.

my $existing_match = data_layer->find('Sale',{id => $id});

Say above returns an array, then use:

if( scalar(@$existing_match) == 0)

edited Dec 18, 2021 at 5:22

brian d foy

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answered Mar 24, 2017 at 16:34

shirish kumar

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1 Comment

lordadmira Over a year ago

The boolean context already takes care of that so writing it all out is redundant.

brian d foy · Accepted Answer · 2021-12-18 05:23:18Z

-3

I've also found that this works too, but I'm not sure if it's documented:

if ($#match == -1)

edited Dec 18, 2021 at 5:23

brian d foy

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answered Dec 16, 2021 at 16:03

Tom Wilson

1

3 Comments

lordadmira Over a year ago

Please, no one ever do this. :) It's always if (@match) { } or if (not @match) { } or if (! @match) { }.

user14166402 Over a year ago

@lordadmira What about if ($#match < -0.5) {}?

user14166402 Over a year ago

In other words, is your objection only that it's dangerous to test for exact equality of two integers in a language where variables are not clearly typed as integer or floating-point?

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