The problem is the empty set of parens in your sub declaration.

sub valid_req() {
#            ^^
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In perl, that is called an empty prototype, and it basically says "This sub never takes any arguments". Which means that

@command = (@_);
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will always result in @command being empty, regardless of what you try to pass in when calling the sub.

If you had strict & warnings* enabled, then you would have been informed of your error with the message

Too many arguments for main::valid_req at ...
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The short term answer is to remove the parens completely, and never use a prototype in perl unless you know that you need to.

The better, long term, answer is to make the transition to using strict and warnings* in your code. It only takes a little while to get used to the few easy steps required to satisfy them.

It just makes life easier.

*References to the warnings pragma added after ambrus's correction below.