Valid unquoted strings, such as bare literal hash keys, consist of \w characters only. They are: A-Za-z0-9 and underscore (_). You can have leading or trailing whitespace, which can come in handy. Hoewever, the - character is not allowed, and forces it to be a normal expression.

Without strict, it's allowed, because without strict it's allowed to use unquoted strings everywhere, not only in literal hash keys and the left operand of the => operator.

# Assuming you don't have subs called POWER and/or NODE.

no strict;

$run{POWER-NODE} = yes;

# equals:

$run{ 'POWER' - 'NODE' } = 'yes';

# equals:

$run{ 0 - 0 } = 'yes';

# and thus:

$run{0} = 'yes';
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Consider:

$foo{99-24} = "Hello, world!\n";
print $foo{75};
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With strict, you can't use the unquoted strings POWER, NODE and yes. You'll have to add quotes as such: $run{'POWER-NODE'} = 'yes'. When you get rid of the -, and use an underscore instead, you can use an unquoted string after all (strict makes an exception for =>'s left operand, and for literal constant hash keys) like this: $run{POWER_NODE} = 'yes'.

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