It's pretty lame that the examples on the page show the answerer not just answering but also talking down to the questioner. XY is a problem that happens a lot, but disparaging people who are trying to learn is not the right response.
Here's how that conversation should have gone:
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Q: How can I echo the last three characters in a filename?
A: If they're in a variable: echo ${foo: -3}
A: However, if what you really want is to get the file extension, it's probably better to handle extensions of any length. Try this instead: ${foo##*.}
A: That expression says to find the longest prefix of `foo` that matches the given glob pattern, and remove it.
Q: Oh wow! That is actually what I wanted, but it hadn't occurred to me that such powerful pattern-matching would be built into the shell. I already had a solution involving piping through sed, but it was pretty slow and ugly. I noticed that all the files I'm operating on have three-letter extensions and I figured there'd be an easier way to take a slice of a string, since that's a common thing to have built-in. But your answer is the best of both worlds. TIL!
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There's really no need to admonish the questioner for starting with the wrong question. That won't help. It will only make them afraid to ask questions at all.
Here's how that conversation should have gone:
---
Q: How can I echo the last three characters in a filename?
A: If they're in a variable: echo ${foo: -3}
A: However, if what you really want is to get the file extension, it's probably better to handle extensions of any length. Try this instead: ${foo##*.}
A: That expression says to find the longest prefix of `foo` that matches the given glob pattern, and remove it.
Q: Oh wow! That is actually what I wanted, but it hadn't occurred to me that such powerful pattern-matching would be built into the shell. I already had a solution involving piping through sed, but it was pretty slow and ugly. I noticed that all the files I'm operating on have three-letter extensions and I figured there'd be an easier way to take a slice of a string, since that's a common thing to have built-in. But your answer is the best of both worlds. TIL!
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There's really no need to admonish the questioner for starting with the wrong question. That won't help. It will only make them afraid to ask questions at all.