Why does trim_end("bom", "dotcom.com") return the original string, while trim_end("com", "dotcom.com") trims as expected?

Question

Why does trim_end("bom", "dotcom.com") return the original string, while trim_end("com", "dotcom.com") trims as expected?

Kooghan Williams 0

I'm working with trim_end() in KQL (Azure Data Explorer) and noticed some confusing behavior when using different combinations of characters to trim a domain string.

Here’s a minimal repro:


let ExampleTable = datatable(domain: string)

[

    "dotcom.com"

];

ExampleTable

| extend trimmed1 = trim_end("com", domain),

         trimmed2 = trim_end("bom", domain),

         trimmed3 = trim_end("moc", domain)

**Expected:** Since all three versions of the `trimChars` set contain the letters `c`, `o`, and `m`, I assumed they would all behave the same — trimming the `.com` suffix from `"dotcom.com"`.

**Actual:**

|domain|trimmed1|trimmed2|trimmed3|
| -------- | -------- | -------- | -------- |
|dotcom.com|dotcom.|dotcom.com|dotcom.|
|dotcom.com|dotcom.|dotcom.com|dotcom.|

Chandra Boorla 15,425 Reputation points Microsoft External Staff Moderator

2025-06-17T19:20:40.94+00:00

@Kooghan Williams

Just checking in to see if the below answer provided by @ Michael Taylor helped.

If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

1 answer

Your answer

Chandra Boorla 15,425 Reputation points Microsoft External Staff Moderator

2025-06-17T19:20:40.94+00:00

@Kooghan Williams

Just checking in to see if the below answer provided by @ Michael Taylor helped.

If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

Answer 1

Michael Taylor 60,601

If you're referring to this function then it trims using a regular expression, not a set of characters. The string com would match and trim only the string value com. Not the individual characters c, o and m. If you want to strip characters then use character groups. Something like this perhaps trim_end("[com]", domain). That would trim the letters c, o and m from the end of the string in any order. So .com would become ., .bom would become .b and xyzmoc would become xyz.

Chandra Boorla 15,425 Reputation points Microsoft External Staff Moderator

2025-06-18T18:05:14.7166667+00:00

@Kooghan Williams

Just checking in to see if the above answer provided by @ Michael Taylor helped.

If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

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Why does trim_end("bom", "dotcom.com") return the original string, while trim_end("com", "dotcom.com") trims as expected?

1 answer

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