To understand a line of PHP

 

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  • Reference — What does this symbol mean in PHP? 18 answers

    • This is the concatenate assignment operator. It will concatenate or add to the end of the string. So: 

    $a = "Hi!";

$a .= " I";
$a .= " love";
$a .= " StackOverflow";
$a .= " a";
$a .= " lot";

echo $a; // echos "Hi! I love StackOverflow a lot"

    In your case 

    $query = "UPDATE authors SET author=UPPER(author) WHERE id=1;";
$query .= "UPDATE authors SET author=LOWER(author) WHERE id=2;";
echo $query; 
/* echos "UPDATE authors SET author=UPPER(author) WHERE id=1; UPDATE authors SET author=LOWER(author) WHERE id=2; */

    It means $query = $query . "UPDATE authors SET author=LOWER(author) WHERE id=2;"; $query = $query . "UPDATE authors SET author=LOWER(author) WHERE id=2;";

    So it appends the String to the Query Variable.

    Your question is about the operator .= . It is a shorthand to a string concatenation followed by an assignment.

    On assigment by operation operators

    There is a family of operators we can call assignment by xyz, where xyz here represents a binary operation on operands of the same type, such as addition, subtraction, concatenation.

    So, let's say we have an operator ⊕: int * int → int , meaning that it takes a pair of int s and produces another one:

    ⊕(a, b) = a ⊕ b

    Let's say we want to calculate a ⊕ b and store the results on the variable a . We can do so by:

    a = a ⊕ b

    But we do this so often when coding that an operator was created to represent the line above. You should take it as a single operation that does both the ⊕ operation and the assignment ( = ) with a single call:

    a ⊕= b ⇔ a = a ⊕ b.

    Some examples

    So, in your case, you have a .= operator. Now that you know about assignment by operation operators, you can guess that: 

    $query = "Hello, "
$query .= "World!";

    is the same as: 

    $query = "Hello, "
$query = $query . "World!";

    See?

    Now, another frequent use of this kind operators are the += and -= versions.

    However, abuse of this kinds of operators may lead to less readable code (especially when dealing with "low level" operators acting on bits, for example).

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