Regex to get each item in an xpath-like string, with each subscript as a group

user_3002584 0
Viewed 69

I'd like to take an xpath-like string such as:

a.b.c[2].d[123].e1[4].f88[5]

And have each path-part as a match, with each subscript ("array index") as a group, like this:

match 1: a
match 2: b
match 3: c, group 1: 123
match 4: e1, group 1: 4,
match 5: f88, group 1: 5

I tried with the following (which doesn't work):

[^.]+(?:\[)*([0-9]+)*(?:\])*

As I understand this Regex, it means:

  1. First, match all characters except for a dot
  2. Then, check (but don't capture) for a left square bracket - it may be present 0 to unlimited times.
  3. Then, check for any number, with length 1 to unlimited - and capture as a group.
  4. Then, do 2 again for a right square brack.

But it doesn't work.

How can I make it work?

grouping regex
2 Answers

[^.]+(?:\[)*([0-9]+)*(?:\])*

"But it doesn't work" because + is greedy and consumes all the characters before the dot. Furthermore, each subscript is integrally optional, rather than part by part.

Applying those criteria, this expression does work:

([^.\[]+)(?:\[(\d+)\])?

Regex101 Test

user_137309970

The pattern that you tried:

  • The pattern that you tried matches too much, as the negated character class [^.]+ matches 1 or more times any char except a dot, and can also match square brackets.

  • Note that this notation (?:\[)* is the same as \[* and matches 0 or more times an opening square bracket

If the \G anchor is supported, and you want to match the example string only from the start of the string, you might use 2 capture groups for the data that you want, and match the dots and square brackets in between.

\G([^\][.\s]+)(?:\[(\d+)\])?\.?

The pattern matches:

  • \G Assert the position at the end of the previous match, or at the start of the string
  • ([^\][.\s]+) Capture group 1, match 1+ char other than ] [ . or a whitespace char (as there do not seem to be any spaces in the example string)
  • (?:\[(\d+)\])? Optionally match capture group 2 between matching square brackets
  • \.? Match an optional dot to continue the consecutive matching for the \G anchor

Regex demo

If there can not be a dot at the end of the string, and there must be at least 1 dot present, you can assert the whole format first from the start of the string:

(?:^(?=[^.]+(?:\.[^.]+)+$)|\G(?!^))\.?([^\][.]+)(?:\[(\d+)\])?

Regex demo

user_54249880
Related