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for (keys %hash) {
    print;
}

for (key %thisisnotintendedasaseriousquestion) {
    print;
}

for (keys %hash) {
    print;
...
for (key %somename) {
    print;
}

I see this in a book:

...

But it doesn't work in my example, please 
<a href="www.somedomain.com/dev/null>look at it here!</a>