I agree that POSIX is needing of a few small additions;
* local keyword
* 2 or 3 variable expansion tricks (string replacement etc)
* pipefail
But with those, I think the spec isn't too bad. I've been writing (imo) high-quality (and shellcheck compliant) shell scripts for a decade, and _always_ try to be as pendantic about being posix compliant where humanly possible. Sometimes things are a _little_ harder (no sarcasm here), but it's really quite doable once you get the hang of it.
You scripts then end up being far more portable, and as stated below, MUCH easier to read. The trick is, to write readable code (which is hard enough for most people, regardless the language anyway :p)
e.g. (a very simple example), and an addition to Shrikant's post, avoid the terse double ampersant 'and' (&&) and double pipe 'or' (||) operators, in normal calls.
do
e.g.
```sh
if ! external_command; then
do something with failure
fi
```
Rather then
`external_command || do something with failure`
These can get up becoming really hard to read once they become longer, where reading a stupid "if" statement is easy to comprehend. Readability over saving number of lines.
One important hint left forgotten, always make sure the last line of your file is `exit 0` or similar. This is more a 'weak' security feature. Prevent people from appending files and executing stuff instead. Gives a known exit point.
Another addition would be to actually favor single quotes for pure strings, and use double quotes where you expect the shell to do something with your string (true for most cases, but there's plenty of strings that benefit from single quotes, and hint the reader what to expect). Also integers should never be quoted (as it would turn then into strings), which shows a 'bad' example in the trace statement, you are now comparing the strings '0' and '1' rather then the number. Best use something easier to read in that case.
One thing I will pick up from this post for sure, is the trace hint, I'm adding that to my scripts, but probably a little more tunable.
```sh
set -eu
if [ -n "${DEBUG_TRACE_SH:-}" ] && \
[ "${DEBUG_TRACE_SH:-}" != "${DEBUG_TRACE_SH#"$(basename "${0}")"}" ] || \
[ "${DEBUG_TRACE_SH:-}" = 'all' ]; then
set -x
fi
echo 'Hello World'
exit 0
```
Though I'll probably just settle for one of those keywords, I like 'all' the best atm. This would run the trace only if this special keyword is given, or if the variable contains the name of the script. I initially had `basename "${0%%.sh}"` but that makes things like `test,test1,test2` impossible, though that only helps if the extension is used ;)
While not needing be part of this list, I personally also always use functions, unless the script really is less then a handful lines, like google's bash-guide, always have a main etc.
In the end though I do disagree writing bash and bashisms. There's plenty of posts about that though; kind of like the whole C++ 'which version to use' discussion, where bash tends to be inconsistent in itself.
Shameless plug: See some of my older stuff here https://gitlab.com/esbs/bootstrap/-/blob/master/docker_boots...