Right string expansion in Bash (for shell script)

Question

I'm experimenting a little bit with a shell script, which should run git commands for multiple repositories on the same level. This project structure might be a bad idea, but this is another story.

Everything works fine until I've run into this problem:

DETAIL="test test" && command="commit -m '${DETAIL}'" && echo $(git ${command})
# -> error: pathspec 'test'' did not match any file(s) known to git.

I've also tried other opportunities like

DETAIL="test test" && command="commit -m ${DETAIL}" && echo $(git ${command})
DETAIL="test test" && command="commit -m $DETAIL" && echo $(git ${command})

All give the same result (see above). I've also scanned these docs about string expansion, but I don't have the problem, that the variables/strings might be null or undefined. The last echo is not the problem, you can also store the result of $(git status) in a variable and echo this one (my way in the script).

I know, there are similar questions, but I did not found a similar scenario yet, since I'm just dealing with simple and non-null strings, but with (too?) many quotes.

Interesting variant:

DETAIL="test test" && command="commit -m '${DETAIL}'" && echo $("git ${command}")
# -> git commit -m 'test test': command not found # WHAT?

Also interesting, just:

command="commit -m 'test'" && echo $(git ${command})

works fine.

KamilCuk · Accepted Answer · 2019-02-12 17:00:15Z

2

Use bash arrays with proper quoting...

DETAIL="test test" && command=(commit -m "$DETAIL") && git "${command[@]}"

To your code:

echo "$(command)" is the same as command (ok, trailing empty newlines are removed)
"command blabla" does not execute file command with the first argument blabla. It will execute a filename named exactly with space command blabla.
Inside $("git ${command}") you want to execute a filename named git commit -m 'test test' (exactly, this is the whole filename name, with spaces, after ${command} is expanded). As on you system there is no file named git commit -m 'test test' bash returns command not found.

edited Feb 12, 2019 at 17:00

answered Feb 12, 2019 at 8:31

KamilCuk

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3 Comments

BairDev Over a year ago

Great, thanks. Now I'm struggling with pouring this array into a local function and getting it right there. Here runCommand is my local function: declare -a commandArray=("commit" "-m" "${DETAIL}"); - next line - run_command $commandArray. Then inside the function: local actualCommand=$@ - then - result=$(git ${actualCommand[@]})?

chepner Over a year ago

bash doesn't have first-class array values. When you say something is an array, it just means that there is an attribute set on the name which allows you to using indexing. It's really a thin layer of syntactic sugar over a set of distinct variables.

KamilCuk Over a year ago

If arr=(1 "2 3" 4), then: f "${arr[@]}" is equal to f 1 "2 3" 4. But f ${arr[@]} is equal to f 1 2 3 4, ie. the " matter. Only "${arr[@]}" will be properly exapanded. Using $arr you will get only first element. You can inside a function local actualCommand=("$@").

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