Multiple unquoted blanks in echo

[sjvudp]

Maybe you want to add this: Multiple unquoted blanks in echo are not flagged, like this:

echo Looking around...       done

(Multiple blanks will be condensed to one)

[arth1]

That may be what you want. echo is often used to strip spaces in bourne shell, like

freespace=$(echo $(df -P / | tail -1) | cut -d' ' -f4)

[deryni]

It may be what you want but it isn't safe in general and if you know you want it then you can tell shellcheck to not warn about it with a directive.

[brother]

@arth1 that line would render shellcheck warnings though. might be usual practice but still not clean enough.

in the case of fetching free space via df using "regular tools" I would turn to awk

df -P / | awk '/^//{print $4}'

for the general case of using echo to clean out spaces you could consider using variable expansions.

[arth1]

Keep in mind that awk and bash aren't always available - especially in embedded.
It's more likely that sed is available, but not guaranteed, and this isn't any prettier:

freespace=$(df -P / | tail -1 | sed 's/[[:space:]][[:space:]]*/ /g' | cut -d' ' -f4)

This is better:

freespace=$(df -P / tail -1 | tr -s '[:space:]' | cut -d' ' -f4)

... but will not work if you also need to trim leading or trailing spaces.

[deryni]

Sure but again in those environments are you virtually guaranteed to be dealing with someone well versed enough to understand the problems and be able to add the shellcheck directive to silence the warning. As opposed to the naive user for whom the whitespace combining is a surprise.

[arth1]

I'm not so sure. One bug here was due to exactly this - one user had in the past written a script that used echo to strip spaces, and another one removed a "useless echo" and added quotes because of shellcheck suggesting it, and the script's functionality broke.
Using echo (glob, actually) to strip extra spaces might not be good programming, but it's common enough practice that I think shellcheck should at least consider whether it could be intentional.

[deryni]

Like we've been saying. It may be common but it is not safe or reliable. Which are the things shellcheck is trying to encourage. It may work for you in your specific examples but it is a bad practice and should be documented (with a directive) as such as far as I'm concerned. The number of people who have problems with this sort of thing on StackOverflow (for example) is enormous.

[koalaman]

I fixed the markup of the original post. It's not about word splitting during expansions but about literal whitespace between shell words.

[deryni]

You know I knew that and yet somehow didn't connect far enough to realize that was a different case entirely. =(
Sorry for the noise.

[koalaman]

A warning is now in place whenever there are 4 or more spaces between words passed to echo on the same line. Thanks!

Smaller gaps were not included because having two spaces was common but seemingly unintentional and harmless, and gaps between echo and the first word appeared to be mostly due to people padding their commands to make their arguments line up.

[sjvudp]

I just realized that "unquotes" should have read "unquoted" (hit the neighbor key) all the time, but it seems I cannot correct it. If possible, correct that.

[sjvudp]

A warning is now in place whenever there are 4 or more spaces between words passed to echo on the same line. Thanks!

Smaller gaps were not included because having two spaces was common but seemingly unintentional and harmless, and gaps between echo and the first word appeared to be mostly due to people padding their commands to make their arguments line up.

But echo a b will be the same as echo a b, but I doubt that the majority deliberately aligns the arguments on echo when the output will be different.

Note: Gitlab messes up the multiple spaces in the code example above: The first one used two spaces between a and b.