Good Bash quoting style

Question

Would you quote this variable assignment which builds a log message from some pre-calculated components?

formatted_message=$(printf '%s [PID %s] %s (%s) %s:%s | %s\n' \
                           "${TIMESTAMP}" \
                           "${PROCESS}" \
                           "${SEVERITY}" \
                           "${SOURCE}" \
                           "${FUNCTION}" \
                           "${LINE}" \
                           "${MESSAGE}")

Is this good Bash programming style actually?

I am loving trying to learn some Bash but there is something which I find "inefficient":

• when there are so many rules about what quotes mean in different contexts, I have to continuously parse (with a "mind compiler") the code I read, and re-read, and re-read, applying some implicit rules which are context-specific (e.g. left side of an expression, right side, expansion applied to an array vs a scalar value, etc.) and that is mentally cumbersome, at least to me. In my simplistic view of the world, having a fixed convention and simple exceptions would allow me to read code faster, write code sometimes with an extra character or two but for the general case very much "automatically" and, especially, recognise exceptions much more readily.

Let's take an example that threw me into this state of confusion about "best coding practices":

[[ $x == "$x" ]]

I can omit the quotes on the left without any real change in behaviour.. adding them to the right side of the evaluation has an important effect. All of a sudden, I wonder about process substitution and all other contexts of "evaluation/substitution" and wish there was one simple way to do it, with few exceptions.

If there was a guiding article/blog post for this I would really study it in detail, coming to an understanding (hopefully) of what a real Bash programmer wants to convey when he/she puts quotes in a particular position of omits them.

Note: my learning happens in a tollbooth at night. I have no fellow programmers apart from you guys here to compare my views with and some open-source code is "just out there", without accompanying comments justifying choices as subtle as "coding style".

Another point: I find it easier to always type:

printf "${my_string_var}"

but of course this is fine as well:

printf "$my_string_var"

(I just happen to "see" the variable expansion better with the {})

but this probably won't be equivalent for word-split variable contents (?!)

printf $my_string_var # with $my_string_var := 'foo bar'

---

Summary

If you just want to answer one simple, straight-forward question and stay clear of a "debate":

• would you quote the first assignment above or not? Why?

Note: one of my problems was that the final \n disappears, even if I try to put double quotes here and there.. but now I understand that $() strips it..

Answer 1

I would not quote the right-hand side, as the usual reason (protect against inadvertent word-splitting) does not apply to the RHS of a variable assignment.

If you are using bash 4 or later, you can dispense with the assignment altogether. Along with that, I find the braces unnecessary and distracting if you don't need them for applying a parameter expansion operator or isolating the parameter name from an adjacent character. Quoting remains important, of course.

printf -v formatted_message '%s [PID %s] %s (%s) %s:%s | %s\n' \
                       "$TIMESTAMP" \
                       "$PROCESS" \
                       "$SEVERITY" \
                       "$SOURCE" \
                       "$FUNCTION" \
                       "$LINE" \
                       "$MESSAGE"