PHP Regex using preg_split

Question

I need to extract from a string 2 parts and place them inside an array.

$test = "add_image_1";

I need to make sure that this string starts with "add_image" and ends with "_1" but only store the number part at the very end. I would like to use preg_split as a learning experience as I will need to use it in the future.

I don't know how to use this function to find an exact word (I tried using "\b" and failed) so I've used "\w+" instead:

$result = preg_split("/(?=\w+)_(?=\d)/", $test);
print_r($result);

This works fine except it also accepts a bunch of other invalid formats such as: "add_image_1_2323". I need to make sure it only accepts this format. The last digit can be larger than 1 digit long.

Result should be:

Array ( 

    [0] => add_image 

    [1] => 1 

)

How can I make this more secure?

`preg_split` isn't the tool to check a format. `preg_match` is better fitted for this task, and if you want to extract parts, use capture groups. — Casimir et Hippolyte, Mar 13 '16 at 22:01

score 1 · Accepted Answer · answered Mar 12 '16 at 22:29

1

Following regex checks for add_image as beginning of string and matches _before digit.

Regex: (?<=add_image)_(?=\d+$)

Explanation:

(?<=add_image) looks behind for add_image
(?=\d+$) looks ahead for number which is end of string and matches the _.

Regex101 Demo

answered Mar 12 '16 at 22:29

ah so that's how you look for exact words, thanks! I was using it all wrong. – Mayron Mar 12 '16 at 22:40
@Mayron: Yes ! you were using `\w+` which means anything in the character class `[A-Za-z0-9_]` repeated several times. – Mar 12 '16 at 22:42
Besides that I made sure that once a number is encountered after `_` there is not other `character` by marking it end of string by `$`. So patterns like `add_image_1_23`, `add_image_9sd` would not be matched at all. – Mar 12 '16 at 22:44
I tried using parenthesis around (add_image) but that didn't work. I also tried using "\b" because I heard that was for capturing full sub-strings. But only your method worked. – Mayron Mar 12 '16 at 22:48
1

`\b` is boundary check. It checks for word boundaries. Read more about it [here](http://www.regular-expressions.info/wordboundaries.html). – Mar 12 '16 at 22:51
1

Thank you! Appreciate it :) – Mayron Mar 12 '16 at 22:56

PHP Regex using preg_split

1 Answers1