I'm trying to match the first number of a comma separated list inside 2 bbcode tags. For instance, I want to match "10" in these 2 cases:

[productid]10,20,30[/productid]  => 10
[productid]10[/productid]  => 10

I'm novice in regex. I've been trying things like this with no luck:

\[productid\](.*)(?=,)\[\/productid\]

Any help will be appreciated! Thank you.

CodePudding user response：

Use this one

\[productid\](\d ?)(?=\D).*\[\/productid\]

• \[productid\] bbcode open tag
• ( Capturing group
  • \d ? Non-greedy number match
• ) Close group
• (?= Lookahead assertion - assert that the following regex matches
  • \D Match anything but numbers
• ) Close lookahead
• .* Match anything
• \[\/productid\] bbcode close tag

See the preview

CodePudding user response：

The most straightforward solution without relying on fancy features like lookahead assertions is \[productid\](\d ).*?\[\/productid\]. Explanation:

1. Opening BBCode tag
2. Greedily match the first number inside the tag
3. Lazily match anything else (including other comma-separated numbers) up to the corresponding closing tag. The lazy matching is required for multiple inline tags such as [productid]10[/productid] inline works too [productid]42,yay[/productid] to work properly; Artyom's solution will fail for those, greedily consuming the entire second tag when parsing the first.