Orijinal soru 
<a href="https://stackoverflow.com/questions/843277/how-do-i-check-if-a-variable-exists">
    Stackoverflow
</a>. 
Soru sahibi: 
<a href="https://stackoverflow.com/users/87152/max-frai">max-frai</a>, 
<a href="https://stackoverflow.com/users/355230/martineau">martineau</a>
Cevaplar 
<a href="https://stackoverflow.com/users/40005/ayman-hourieh">ayman-hourieh</a> 
ve 
<a href="https://stackoverflow.com/users/14860/paxdiablo">paxdiablo</a>. 
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