Comment 4 for bug 141481

First, we have to make a distinction between the issues described here which are POSIX and which mean that there is a bug in dash that should be fixed, and those which are NOT POSIX, of which, contrary to the assertion above, there are definitely some. For example:

$ dash -c 'a=water;echo ${a:2:2}'
dash: Syntax error: Bad substitution

is not POSIX: POSIX does not define substring syntax. Also:

$ dash -c 'echo $UID'
# no output. how on earth are we supposed to safely and portably get the UID?

POSIX does not define that the shell should set the UID variable. You have to use "id".

$ dash -c 'x="1 2"; local y=$x; echo $y'
local: 1: 2: bad variable name

I don't think "local" is defined in POSIX sh, although it appears dash does try to implement it; if so it should be done right.

$ dash -c 'cnt=6; while [ $((cnt = cnt - 1)) -gt 0 ]; do echo $cnt; done'
dash: arith: syntax error: "cnt = cnt - 1"

I don't think assignment inside arithmetic expressions is defined in POSIX.

The rest of these do appear to be bugs in dash, although technically the POSIX spec only guarantees the shell to handle file descriptors 0-9 so using any FD >9 is not, strictly, portable.

My opinion is that Ubuntu is 100% correct here: they should be using POSIX shell scripts and any script that does not adhere to POSIX should NOT start with #!/bin/sh. Obviously where dash doesn't support POSIX that's a bug in dash that needs to be fixed.

But, I hope Ubuntu will not bow down to this decade's version of "all the world's a VAX" and make more true the maxim "every /bin/sh is bash".

Fight the good fight, Ubuntu!