Regex that will match PHP variable but not object and function invocation

Question

I am working on a regex that will match one of

$foo $bar $baz

but not

$foo->bar

So far, I have

/\$([a-zA-Z_][a-zA-Z_0-9]*(?!->))/

Unfortunately, this pattern matches $fo. See this regex demo.

Answer 1

Use a possessive quantifier that will disallow backtracking into the [a-zA-Z_0-9] subpattern:

\$([a-zA-Z_][a-zA-Z_0-9]*+(?!->))
                        ^^

or even (as [a-zA-Z_0-9] = \w if you are not using /u modifier or (*UCP) verb):

\$([a-zA-Z_]\w*(?!->))

See regex demo

The issue is that when the negative lookahead fails backtracking gets into play, and as * allows backtracking into the quantified subpattern, the o that is not followed with -> is found and a match is returned.

See how your regex works, pay special attention at the backtracking steps: