Wtf. All these years I thought 'touch' was reference to Michelangelo's Creation of Adam.

Yeah. It could just as well have issued a file not found error when you try to touch a nonexistent file. And we would be none the wiser about what we're missing in the world.

This is an interesting idea to allow non-root users to restart a service. It looks like this is doable with systemd too. https://superuser.com/a/1531261

$ cat file1 > output_file
$ cat file2 >> output_file
$ cat file3 >> output_file

I'm sorry!

That's its intended purpose - combining files together (the opposite of split). See the first line of the man page: https://man7.org/linux/man-pages/man1/cat.1.html

It is short for concatenate, which is to join things together. You can give it multiple inputs and it will output each one directly following the previous. It so happens to also work with just one input.

It is to use along with split. e.g.

1. You take a single large file, say 16GB
2. Use split to break it into multiple files of 4GB
3. Now you can transfer it to a FAT32 Removable Flash Drive and transfer it to whatever other computer that doesn't have Ethernet.
4. Here, you can use cat to combine all files into the original file. (preferably accompanied by a checksum)

it now has a hot reload, How long ago were you using Django?

The POSIX standard is more portable. If you are writing scripts for your system, you can use the full features in the main man pages. If you are writing code that you want to run on other Linux systems, maybe with reduced feature sets like a tiny embedded computer or alternates to gnu tools like alpine linux, or even other unixes like the BSDs, you will have a better time if you limit yourself to POSIX-compatible features and options -- any POSIX-compatible Unix-like implementation should be able to run POSIX-compliant code.

This is also why many shell scripts will call #!/bin/sh instead of #!/bin/bash -- sh is more likely to be available on tinier systems than bash.

If you are just writing scripts and commands for your own purposes, or you know they will only be used on full-feature distributions, it's often simpler and more comfortable to use all of the advanced features available on your system.

If you execute a binary without specifying the path to it, it will be searched from the $PATH environment variable, which is a list of places to look for the binary. From left to right, the first found one is returned.

You can use which cat to see what it resolves to and whereis cat to get all possible results.

If you intentionally wants to use a different binary with the same name, you can either directly use its path, or prepend its path to $PATH.

You would love Linux cli.

Sorry, what?

Yup, stupid zip files and their directories from 1970

Well, those aren't really the intended use either.