Q:

What does the | operator do when it appears in the md5() parameters?

In a piece of code originally not written by me, I found this:
md5($variable1|$variable2|$variable3)

I know the code is encrypting something using md5. What I am trying to understand is what the | operator is doing when used in this way.
UPDATE 1: It is not concatenating of course. It would make sense to me something like this:
$finalString = $variable1.$variable2.$variable3;
md5($finalString);

But | is the OR operator. I am trying to understand what md5($variable1|$variable2|$variable3) does, using the | operator as part of the parameters within the md5() method. This is PHP code by the way.

A:

The pipe operator | indicates that a bitwise OR is taking place between your three variables.
However, if $variable3 is textual as you indicate, then I do not understand why you would be doing this.
Take a look at the code below. It utilises the example data you posted in the comments:
$variable1 = 2432;
$variable2 = 3234322;
$variable3 = 'adtw2GEt4PrPghhfLApae';

echo '1: ' . $variable1 . '<br />';
echo '2: ' . $variable2 . '<br />';
echo '3: ' . $variable3 . '<br /><br />';

echo '1|2: ' . ($variable1 | $variable2) . '<br />';
echo '1|2|3: ' . ($variable1 | $variable2 | $variable3) . '<br /><br />';

echo '1.2: ' . ($variable1 . $variable2) . '<br />';
echo '1.2.3: ' . ($variable1 . $variable2 . $variable3) . '<br /><br />';

echo 'md5 1|2|3: ' . md5($variable1|$variable2|$variable3) . '<br />';
echo 'md5 1.2.3: ' . md5($variable1.$variable2.$variable3) . '<br />';

You'll see straight away that 1|2 gives the same result as 1|2|3, meaining that the second bitwise OR does nothing (because it is a string):
1|2: 3234706
1|2|3: 3234706

If you treated all three variables as a string then you will get a totally different MD5 hash, as you'd expect:
md5 1|2|3: fdea81fcefba5a598cf3124d7dbf3854
md5 1.2.3: 8cc6383034ed459ad7a135fcb8cb86de

So md5($variable1|$variable2|$variable3); is the same as md5(3234706); (which is just $variable1|$variable2) and doesn't even use the third variable.
MD5 is not encryption: I notice that you mentioned encryption in the comments. MD5 is not encryption, it is a hashing algorithm, which is altogether different.

