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PHP Manual

Getting A Set of Documents With a Query

We can use the query to get a set of documents from our collection. For example, if we wanted to get all documents where "i" > 50, we could write:

<?php
$connection = new MongoClient();
$collection = $connection->database->collectionName;

$query = array( "i" => array( '$gt' => 50 ) ); //note the single quotes around '$gt'
$cursor = $collection->find( $query );

while ( $cursor->hasNext() )
{
    var_dump( $cursor->getNext() );
}
?>

which should print the documents where "i" > 50. We could also get a range, say 20 < i <= 30: 

<?php
$connection = new MongoClient();
$collection = $connection->database->collectionName;

$query = array( 'i' => array( '$gt' => 20, "\$lte" => 30 ) );
$cursor = $collection->find( $query );

while ( $cursor->hasNext() )
{
    var_dump( $cursor->getNext() );
}
?>

Remember to always escape the $-symbol or use single quotes. Otherwise PHP will interpret it to be the variable $gt.