Comment by susam | Hacker News Reader

Comment by susam | Hacker News Reader

Parent Full thread

> Aren't people targetting bash or basic bourne shell features intead of posix?

I know many banks still have AIX systems with shells like ksh89, ksh93, etc. as the default shell. So if a shell script is written to work with a POSIX shell (instead of a particular shell), it has a better chance of running on such systems.

Also, on Debian, the default non-interactive shell is dash [1]. This is the Debian Almquist Shell (dash). It is a POSIX-compliant shell derived from ash. So again, if we write system scripts for Debian and want it to run on Debian without any hassle, it makes sense to write the system scripts to conform to POSIX shell. Although shellcheck cannot perform full POSIX compliance check at this time, it is still a pretty good tool that can help with checking compliance with dash in particular.

[1]: https://packages.debian.org/stable/dash

> So again, if we write system scripts for Debian and want it to run on Debian without any hassle, it makes sense to write the scripts to conform to POSIX shell.

Or explicitly use bash in your shebang.

One of the problems with Bash is that it insists on doing bash-y things even when you tell it to act like sh.

People ask why you should write (or at least test) code to be multi-platform (even the basics of running it on BSD or macOS): it's because it forces you to be honest. Things change and initial assumptions may not be the same forever.

* https://wiki.debian.org/Shell

* https://archlinux.org/packages/?name=checkbashisms

* https://wiki.ubuntu.com/DashAsBinSh

> One of the problems with Bash is that it insists on doing bash-y things even when you tell it to act like sh.

Its behaviour is a common behaviour of all sh, not just Bash.

Bash has `Priority: required` and is marked as "essential", it's available on every Debian system.

Indeed, Bash is always available on Debian! After all, Debian uses Bash as the default interactive shell. But that's not the point of writing system scripts for dash. They are written for dash because that's still the default non-interactive shell. And it is so because dash is leaner and faster. Quoting from the link I posted in my previous comment:

> Since it executes scripts faster than bash, and has fewer library dependencies (making it more robust against software or hardware failures), it is used as the default system shell on Debian systems.

Reply on news.ycombinator.com