# Tricky #ao7 case "^dog$" not matching "dogdogdog"

**URL:** <https://forum.codecrafters.io/t/tricky-ao7-case-dog-not-matching-dogdogdog/9136>\
**Category:** Challenges\
**Tags:** challenge:grep\
**Created:** [April 21, 2025, 10:04am UTC](https://forum.codecrafters.io/t/tricky-ao7-case-dog-not-matching-dogdogdog/9136 "2025-04-21T10:04:18Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![HowieTKL](https://yyz1.discourse-cdn.com/flex003/user_avatar/forum.codecrafters.io/howietkl/32/5687_2.png) [@HowieTKL](https://forum.codecrafters.io/u/HowieTKL)\
**Post date:** [April 21, 2025, 10:04am UTC](https://forum.codecrafters.io/t/tricky-ao7-case-dog-not-matching-dogdogdog/9136/1 "2025-04-21T10:04:18Z")

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According to grep behavior:

```auto
echo dogdogdog | grep -E "^dog$"

```

does NOT match. However, individually `^dog` and `dog$` will match `dogdogdog`. I do not believe the test cases capture this seemingly quirky scenario either.

But I’m stumped trying to mimic grep behavior for `^dog$` with `dogdogdog`. It does not seem possible by simply checking string “starts with” `dog` for `^` and “ends with” `dog` for `$`. Anyone have any insights on how to think about `^$`?

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**Author:** ![andy1li](https://yyz1.discourse-cdn.com/flex003/user_avatar/forum.codecrafters.io/andy1li/32/10_2.png) [@andy1li](https://forum.codecrafters.io/u/andy1li)\
**Post date:** [April 21, 2025, 3:03pm UTC](https://forum.codecrafters.io/t/tricky-ao7-case-dog-not-matching-dogdogdog/9136/4 "2025-04-21T15:03:57Z")

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> Anyone have any insights on how to think about `^$` ?

Hey @HowieTKL, a helpful way to think about `^$` is that it means **match the entire line exactly**.

Namely, the pattern `^dog$` is equivalent to `line == "dog"`:

 ![image](https://canada1.discourse-cdn.com/flex003/uploads/codecrafters/original/2X/e/e4a25df16bdbdfc5ffc1e362b5f58e73ac6af56d.png)

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<div class="post-metadata">

**Author:** ![HowieTKL](https://yyz1.discourse-cdn.com/flex003/user_avatar/forum.codecrafters.io/howietkl/32/5687_2.png) [@HowieTKL](https://forum.codecrafters.io/u/HowieTKL)\
**Post date:** [April 27, 2025, 9:48am UTC](https://forum.codecrafters.io/t/tricky-ao7-case-dog-not-matching-dogdogdog/9136/6 "2025-04-27T09:48:56Z")

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Thanks @andy1li - just refining what you said: I think `^` can be read as “matches exactly from the start” and `$` as “matches exactly from the end”.

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<div class="post-metadata">

**Author:** ![system](https://canada1.discourse-cdn.com/flex003/uploads/codecrafters/original/3X/7/0/700657133935c15703e22c7c8870394f6e6dc27d.svg) [@system](https://forum.codecrafters.io/u/system)\
**Post date:** [May 2, 2025, 9:49am UTC](https://forum.codecrafters.io/t/tricky-ao7-case-dog-not-matching-dogdogdog/9136/7 "2025-05-02T09:49:12Z")

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