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Comment by francis-io | Hacker News Reader

Can you explain why?

For portability. bash is not available everywhere, but POSIX sh is a requirement of POSIX so you can expect it to be there.

Exactly: GNU bash is on most GNU/Linux systems, but:

* mac OS uses an ancient version of bash

* Embedded systems use busybox sh

* Android uses its own version of sh

* None of the BSDs come with bash, since, y'know GNU licensing

EDIT: Formatting

And to make things interesting Ubuntu uses dash as sh

https://wiki.ubuntu.com/DashAsBinSh

In fairness, that's just for sh; if for some reason you actually need bash you can just use `#!/usr/bin/env bash`

If you actually //need// bash ask for it, not sh.

This comes from more armature script authors not being precise enough with requirements, or not targeting the more common and portable spec.

`sh` is only supposed to be _a_ POSIX-compliant shell, it's not odd/interesting/confusing that Ubuntu uses dash any more than it is that something else uses bash.

The shebang line #!/bin/sh should only be used for POSIX-compliant scripts; if it needs {bash, dash, python, etc.} it should start #!/usr/bin/env {bash, dash, python, etc.}.

Not all systems have bash.

Not all systems have POSIX, perl, python, javascript, C++, rust, go, etc., so should we write all our programs and scripts in sh?

The relevant point is that all systems running bash should also be POSIX compliant. So, taking some care to avoid bash-only constructs in a shell script can reap substantial gains in portability at fairly minor cost.

Why I should care about all systems? If targeted systems have bash4.x and GNU tools, why I should write scripts in sh? If you care about all systems, ANSI C is better choice, IMHO.

If you're targeting a limited set of systems and can reasonably assume the requirements won't change in the future, obviously use whatever tools you know will be available. I write Bash and Python all the time for those reasons.

But it's silly to think that there's nothing in between "complete control over target environment" and "use ANSI C so it can be compiled to any architecture and platform under the Sun." POSIX compliance will cover a lot. Try browsing /usr/bin on any Unix system you'll see plenty of use cases. I just looked at /usr/bin on my laptop and saw that mysqld_safe is a Bourne shell script, for just one example.

less magic (which you start to care for if you have to use other people's magic), easier to port stuff to zsh, etc.

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