[SOLVED] Bash single-quote elements of array and concatenate using space

Issue

I have an array in Bash that may be empty. I need to convert the array to a single string, placing a single quote around each element, and separating the elements with a single space. For example:

• (): ""
• ("test"): "'test'"
• ("foo bar"): "'foo bar'"
• ("test" "foo bar"): "'test' 'foo bar'"

Assume my array is in $array, and I put the result in $result. I'm wanting to pass the result as arguments to Maven exec:java exec.args, like this:

array=("test" "foo bar")
result= # TODO
mvn exec:java -Dexec.mainClass="org.example.Main" -Dexec.args="$result"

This would be equivalent to:

mvn exec:java -Dexec.mainClass="org.example.Main" -Dexec.args="'test' 'foo bar'"

Importantly, note that if the array is empty, it would be equivalent to:

mvn exec:java -Dexec.mainClass="org.example.Main" -Dexec.args=""

I would have thought that this would have been answered two decades ago—and maybe it has been, but I can't find it. I found Bash script pass arguments to maven, which has no answer. I found various answers relating to joining with a delimiter, but couldn't find anything that would single-quote each element, join with a delimiter, and still produce an empty string if the array is empty.

For example, Concat array elements with comma and single quote - Bash comes very close:

array=("test" "foo bar")
joined=$(printf " '%s'" "${array[@]}")
result="${joined:1}"
mvn exec:java -Dexec.mainClass="org.example.Main" -Dexec.args="$result"

But if the array is empty, I get "''" when I want "". Update: I guess I can do an old-fashioned if to special-case an empty array. Anyone have anything better?

Solution

You can use @Q operator (shell parameter expansion - @operator):

array=("test" "foo bar")
result="${array[*]@Q}"
mvn exec:java -Dexec.mainClass="org.example.Main" -Dexec.args="$result"

If both single/double quotes can appear in the array, consider this :

array=("foo'bar" 'foo"bar')

mapfile -t array2 < <(perl -e '
    for $_ (@ARGV) {
        $q = /"/ ? "'\''" : q["];
        print "$q$_$q\n";
    }' "${array[@]}")

result="${array2[*]}"

This assumes that only one type of quotes can appear in a single item of the array though.

Answered By - Philippe

Answer Checked By - Katrina (WPSolving Volunteer)