Ensure POSIX-compliant shell scripting to support DASH

Some systems, such as Ubuntu, use DASH to provide /bin/sh instead of BASH. This means that we need to use POSIX compliant shell scripting as BASHisms are unsupported in DASH. There are two BASH variable substition instances within the code of xdg-settings.in that cause KDE users to be unable to find the current web browser because the script dies when hitting this unsupported code.

DASH also doesn't support the BASHism that allows == inside [] tests.

• Replace ${variable:0:1} with printf-based equivalent.
• Replace use of == with =

Fixes #10 (closed), #203 (closed)

Signed-off-by: Lucy Llewellyn lucyllewy@ubuntu.com

changed the description

added 1 commit

• fcac7f9c - Replace BASH substitutions with printf

Compare with previous version

Sorry, I just force pushed because I needed to fix the commit message. This is good to go.

When testing this on Ubuntu 22.04 in the context of https://bugs.launchpad.net/ubuntu/+source/xdg-utils/+bug/1970594, I'm observing this:

$ xdg-settings check default-web-browser firefox.desktop
/usr/bin/xdg-settings: 734: [: x!: unexpected operator
yes

So the output is as expected, but there is an "unexpected operator" error on stderr.

It looks like DASH doesn't like "!" while BASH is ok with it. I think the solution is to escape it with "\!"

added 1 commit

• 72275fa6 - Add string escaping to appease DASH on Ubuntu

Compare with previous version

mentioned in issue #203 (closed)

added 1 commit

• 8996594d - Fix use of `==` to `=` for Ubuntu, because DASH doesn't support `==` inside `[]` tests

Compare with previous version

resolved all threads

LGTM. I was struck by this bug on Kubuntu 22.04 and running with this patch fixes the issue for me.

Thanks! For information, I have uploaded the updated patch to Ubuntu 22.10 (and will SRU it to 22.04 in due course): https://launchpad.net/ubuntu/+source/xdg-utils/1.1.3-4.1ubuntu3.

Great thanks.

I think it is not ideal to use printf and subshell. You could use POSIX parameter expansion, instead. Also ${browser:1} and ${binary:1} should be modified.

mentioned in merge request !54 (closed)

Good catches. I also fixed another bashism in !24 (17c7c995).

It's maybe worth noting in the commit message that == is a non-portable alias in bash that is exactly identical to =.

Personally, I'm disappointed that it even exists in bash -- it doesn't really do anything other than confuse people, I strongly recommend using = even in bash scripts.

...

Anyway, it is incorrect to mention Ubuntu, or alternatively, the commit message should probably say "systems such as Ubuntu". There are certainly other systems where the sh shell is dash or another non-bash shell. :)

Also Fixes #203 (closed), let me see if I can add that to the overview to auto close that bug

changed the description

mentioned in issue #165 (closed)

added 1 commit

• a114fc51 - Ensure POSIX-compliant shell scripting to support DASH

Compare with previous version

changed title from Replace BASH substitutions with printf to Ensure POSIX-compliant shell scripting to support DASH

changed the description

I've squished the commits and reworded the commit message and the description here.

added 24 commits

• a114fc51...5f14673f - 23 commits from branch xdg:master
• 301a1a47 - Ensure POSIX-compliant shell scripting to support DASH

Compare with previous version

merged

Merged, thanks for your work.