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I have read some time ago (can't find the reference) that using such an alias as alias rm="rm -i" was very bad.

Is there historical evidence or common sense explanation for that fact?

I would imagine that it gives a user a bad habit of relying on the confirmation prompt to check his command, which could lead to disasters if he does so on another profile that doesn't have the alias.

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possible duplicate of Best practices to alias the rm command and make it safer – Daniel Beck Feb 1 '12 at 15:12
    
I think I found the topic you mentioned. – Daniel Beck Feb 1 '12 at 15:12
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@Daniel indeed the most upvoted answer of this thread mentions this bad practice, but it is not really the question's central topic. – Dunaril Feb 1 '12 at 15:49
up vote 30 down vote accepted

You're right.

It's bad because you get used to it. If you're on a system that doesn't have it, and you rm, it immediately starts deleting and you're wondering what's going on.

Many users are used to SSH'ing into different systems; so using lots of different systems, sometimes without personalized user accounts (including aliases) set up, is rather common.

Instead, use e.g. alias rmi='rm -i' and learn to use that one. If that isn't set up on a different system, you didn't accidentally delete files and can always fall back to typing the full command.

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Like @Daniel said, it's not harmful in and of itself, other than training you to expect it to be there. In fact, it's the default set-up on CentOS (and by extension RHEL, I presume - been too long since I've used one) machines, and it's a massive pain in the tuchus. For the rest of my time at that gig, I typed /bin/rm in order to avoid the "Linux for people who shouldn't have root access" setup.

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RHEL has this by default, you're right, at least the systems I used. – Daniel Beck Feb 1 '12 at 15:18

I think the big danger is that people might rely on something like this to filter a glob. Imagine you want to delete some images from a directory, but not all of them:

rm -i pics/*.jpg

You could use that to filter the glob manually, which would be completely reasonable. But, if you had aliased it and were using rm and happened to land in a shell without that alias and try it... you just deleted all your pictures, oops!

Personally I also find this alias to be harmful to my blood pressure ;). But that's just me.

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Nice example. Of course if you like danger, or gambling.. – Dunaril Feb 1 '12 at 15:54

In addition to what Daniel Beck said, I found myself using -f to bypass the -i, which is potentially dangerous as it results in using rm -f and rm -rf unnecessarily. Somehow related: a way to prevent rm -rf issues is this is to create file called "-i" as duscissed in answer of this question:How do I prevent accidental rm -rf /*?.

But again, if that alias wasn't there, I wouldn't use -f, and the whole thing won't be an issue.

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Looks like you found a way to make this bad practice even worse :) – Dunaril Feb 1 '12 at 15:51

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