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Comment by cure | Hacker News Reader

> That advice can cause substantial headache on Ubuntu/Debian, where the Almquist shell is /bin/sh. This does not implement much of bash and will fail spectacularly on the simplest of scripts. This is also an issue on systems using Busybox.

At least for Debian and Ubuntu, that's why we start bash scripts with #!/bin/bash, of course.

Your point is valid for Busybox, though.

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> that's why we start bash scripts with #!/bin/bash

That will also fail spectacularly, as bash does not behave the same when called as /bin/bash as it does when it is /bin/sh.

I have principally noticed that aliases are not expanded in scripts unless a shopt is issued, which violates POSIX.

Forcing POSIXLY_CORRECT might also help.

I would assume if you put /bin/bash as your shebang that you're expecting to get bash-isms. I think the problem you're complaining about (which is a real one) is people putting /bin/sh and expecting bashisms. Debuntu being problematic here is more a side effect of bad practice.

Bash has a POSIX mode.

Knowing when to switch into and out of this mode, and what impact it has, is a more advanced subject that should not burden those learning the Borne family.

It is better to start with Almquist, or another pure POSIX implementation, with documentation specific to standard adherence.

More advanced shell features should wait.

I have mixed feelings. On paper I agree with you, people should start with POSIX shell. In practice I'm not sure how relevant that is anymore. I'm not really convinced bash should be the default thing people learn, but I think there's a decent argument that people should just start off with the shell they're going to actually use. You should, however, be aware that there is a distinction, and if you're learning/writing bash and not POSIX shell you should specify /bin/bash not /bin/sh. But you don't necessarily need to know all the nuances of how bash differs unless you have a need to write POSIX compliant shell.

For me, I just want a shell that works.

Without a nuanced understanding of standards, extensions, and platform availability, new bash users will get large amounts of shell usage that doesn't work.

To avoid that frustration, learn POSIX. That works everywhere that matters.

Not sure what you are saying, bash behaves as bash when invoked as /bin/bash, and Bourne-shell-ish when invoked as /bin/sh. Lots more detail in the man page.

I've never seen use of aliases in a bash script...? They are generally for CLI convenience.

Alias expansion within scripts is mandated by POSIX.

When bash is not in POSIX mode, it violates the standard.

  $ ll /bin/sh
  lrwxrwxrwx. 1 root root 4 Nov 24 08:40 /bin/sh -> bash

  $ cat s1
  #!/bin/sh
  alias p=printf
  p hello\\n

  $ cat s2
  #!/bin/bash
  alias p=printf
  p world\\n

  $ ./s1
  hello

  $ ./s2
  ./s2: line 3: p: command not found

That's very nice, it's POSIX-compliant when invoked as #!/bin/sh and sane when invoked as #!/bin/bash — exactly what I'd want.

If you want a portable script, then you don't want that behavior.

Then I wouldn't put #!/bin/bash at the top.

Your problem there is Ubuntu/Debian.

A bash script that runs as /bin/sh might not run as /bin/bash, until you set POSIXLY_CORRECT.

Easiest solution there is to move it to a better shell, usually a Korn variant.

Sure but someone putting #!/bin/bash at the top of their script, written for non-POSIX bash, won't have that issue...

Why would anyone want to target bash specifically which doesn't exist in all systems instead of just sticking to what's implemented in /bin/sh?

Because you're not going to have a great time with /bin/sh (i.e. dash or the like) if you want to do anything more than very, very basic scripts.

Relying on bash is a recipe for non-portability.

If you're not publishing your scripts and you're running your own infrastructure, you probably don't care about portability at all.

None of the BSDs use bash in their base. Apple recently switched from bash to zsh. OpenBSD uses a descendent of pdksh.

Another major user of a pdksh descendent is Android (mksh), with a truly massive install base.

Some of the bash problem, besides portability, is GPLv3. That was a major factor for Apple. I don't want my script portability linked to corporate patent issues. For this and other reasons, I don't use bash-specific features, ever.

Yeah I've written and maintained scripts for the past 10 years that have to run on stock Solaris, AIX and *BSD. When they started out they had to work on the Solaris 9 /bin/sh, which is particularly elderly.

You should feel free to continue to write portable scripts.

That is horrible advice for anyone who is just starting out though and they should stick with #!/bin/bash and not worry about it until they actually want to consider platforms other than Linux. Portability is the wrong thing for people who are learning to focus on.

It is also bad advice for most system administrators at most businesses since they won't have those alternative *nixes either, and its a best practice to minimize how many different operating systems you have to care about.

As we've already covered, Ubuntu is your downfall.

Almquist is in Ubuntu for two reasons: speed and standards compliance.

These may not be important to you, but they are to a great many people, and the horrible advice in this case is to disregard these factors.

#!/bin/bash

People who start out with linux should use that. Most companies, particularly HNey startups, should use that and nothing bad will happen.

Most people don't have to care about portability, shouldn't use /bin/sh, and shouldn't learn about Almquist. Your advice does not favors to the bulk of people who just need to get shit done.

If they do wind up working in an environment where it is important, they can teach themselves the differences at that point, or else ask someone like us to review their code (and there's an automated linter out there).

You aren't the Main Character, most people don't need to care about the same things that you do.

You don't really know exactly what you'll get with /bin/sh - you might get bash trying to behave like sh, you might get dash. At least with /bin/bash you're hopefully getting bash. Now you just have to wonder what version...

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