if (/$hash{$whatever}/) {
    do something;
}

##</code><code>##

%SampleHash (
    'whatever' =&gt; 'whatever',
    'whoever' =&gt; 'whoever',
)

##</code><code>##

if($SampleHash{$string}){ ... }

##</code><code>##

foreach(LIST) {
    $checked{$_}++;
}

if($checked{$string}) { ... }

##</code><code>##

@checked{LIST} = ();

if(exists $check{$string}) { ... }