Characters that can follow a $variable in PHP - php

Question

I am looking for a list of characters that can follow a $variable in PHP. Original task is to go through a file and replace every instance of a variable with different text. But if a file contained $cat and $cat2 and I simply replaced every instance of $cat with $dog, I'd have $dog2 and could not replace $cat2 with $dog3 if I wanted.
Possible solution: order by length and do longest variables first?
The most obvious ones: ),.&+-/*:;%?=[<>!|
For example, you could have a PHP file that had lines like this:
$var = explode($sep, $text);
As you can see, variables are followed by " ", "," and ")" in that line.
What other ones am I missing? Thanks for help, guys.

Answer 1

Implemented it just for fun (even though I still don't understand why you need that):
$code = '<?php
$cat = "foo";
$cat2 = "bar";
$dog = "baz";
';
$replace = array(
'cat' => 'dog',
'cat2' => 'not_dog',
'dog' => 'cat',
);
$tokens = token_get_all($code);
$newCode = '';
foreach ($tokens as $token) {
if (is_array($token)) {
if ($token[0] == T_VARIABLE) {
$variableName = substr($token[1], 1);
if (array_key_exists($variableName, $replace)) {
$token[1] = sprintf('$%s', $replace[$variableName]);
}
}
$part = $token[1];
} else {
$part = $token;
}
$newCode .= $part;
}
echo $newCode;
Demo: http://ideone.com/WUlRdo

Answer 2

From the PHP manual -
Variable names follow the same rules as other labels in PHP. A valid variable name starts with a letter or underscore, followed by any number of letters, numbers, or underscores. As a regular expression, it would be expressed thus: '[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*'
So there you go - if you want to replace all instance of a variable, you just negate the second character class in that regular expression.
preg_replace('/\$replaceMe([^a-zA-Z0-9_\x7f-\xff]|$)/', '$bar', $myCode);

Answer 3

In addition to the ones you posted:
Whitespace and new lines
( as in: $obj = new $variableClassName()
See variable variables
\ to escape characters after a variable inside double quoted string, like "\"$variable\""
# for line comments, as in $variable#comment