What is the .= (dot equals) operator in PHP? [duplicate] - php

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Reference Guide: What does this symbol mean in PHP? (PHP Syntax)
(24 answers)
Closed 8 years ago.
What does the following line mean, particularly the operator .=?
$query .= "UPDATE authors SET author=LOWER(author) WHERE id=2;";
in the code
<?php
$conn = pg_pconnect("dbname=publisher");
// these statements will be executed as one transaction
$query = "UPDATE authors SET author=UPPER(author) WHERE id=1;";
$query .= "UPDATE authors SET author=LOWER(author) WHERE id=2;";
pg_query($conn, $query);
?>
It seems to make some sort of array such that the last command processes first the first query and then the second.

Answer 1

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; */

Answer 2

It means $query = $query . "UPDATE authors SET author=LOWER(author) WHERE id=2;";
So it appends the String to the Query Variable.

Answer 3

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 ints 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).

Answer 4

.= simply means "append". This
$query = "UPDATE authors SET author=UPPER(author) WHERE id=1;";
$query .= "UPDATE authors SET author=LOWER(author) WHERE id=2;";
…results in
$query == "UPDATE authors SET author=UPPER(author) WHERE id=1;UPDATE authors SET author=LOWER(author) WHERE id=2;"

Answer 5

it separates the updates with ; and executes both of them

Answer 6

Concatenates the string... so $query becomes:
"UPDATE authors SET author=UPPER(author) WHERE id=1;UPDATE authors SET author=LOWER(author) WHERE id=2;"