Question

One of the HTML input fields in an app I’m working on is being validated with the following regex pattern:

.{5,}+

What is this checking for?

Other fields are being checked with this pattern which I also don’t understand:

.+

Answer 1

We can break your pattern down into three parts:

The dot is a wildcard, it matches any character (except for newlines, by default, unless the /s modifier is set).

{5,} is specifies repetition on the dot. It says that the dot must match at least 5 times. If there was a number after the comma, the dot would have to match between 5 and that number of times, but since there’s no number, it can match infinite times.

In your first pattern, the + is a possessive quantifier (see below for how + can mean different things in different situations). It tells the regular expression engine that once it’s satisfied the previous condition (ie. .{5,}), it should not try to backtrack.

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Your second pattern is simpler. The dot still means the same thing as above (works as a wildcard). However, here the + has a different meaning, and is a repetition operator, meaning that the dot must match 1 or more times (that could also be expressed as .{1,}, as we saw above).

As you can see, + has a different meaning depending on context. When used on its own, it is a repetition operator. However when it follows a different repetition operator (either *, ?, + or {...}) it becomes a possessive quantifier.