Suppose I have an array foo that looks like the below, notice the third element.
foo=("a" "b" "c c")
echo "${foo[2]}" # "c c"
echo "${#foo[@]}" # "3"
How might I create an exact duplicate of that array into a variable bar?
And then if you want to pass that array (by value) into a function baz?
Edit: Moved answer to answer.
If you want to pass an array by reference (which is what your code actually does), bash 4.3 allows this to be done with namevars:
foo=( hello "cruel world" )
print_contents() {
local -n array=$1
printf '%q\n' "${array[@]}"
}
print_contents foo
If you want to pass by value, even easier (and functional even with ancient releases):
foo=( hello "cruel world" )
print_contents() {
printf '%q\n' "$@"
}
print_contents "${foo[@]}"
If you want to pass multiple arrays by value, by contrast:
foo=( hello "cruel world" )
bar=( more "stuff here" )
print_arrays() {
while (( $# )); do
printf '%s\n' "Started a new array:"
local -a contents=()
local array_len
array_len=$1; shift
for ((n=0; n<array_len; n++)); do
contents+=( "$1" ); shift
done
printf ' %q\n' "${contents[@]}"
done
}
print_arrays "${#foo[@]}" "${foo[@]}" \
"${#bar[@]}" "${bar[@]}"
I ended up finding my answer as I was writing the question. Here's the train of thought.
Several attempts below
bar=foo # String "foo"
bar=$foo # First element of array foo "a"
bar=${foo[@]}
echo "${#bar[@]}" # "1"
echo "${bar[0]}" # "a b c c"
bar=(${foo[@]})
echo "${#bar[@]}" # "4"
echo "${bar[2]}" # "c"
echo "${bar[3]}" # "c"
bar=("${foo[@]}")
echo "${#bar[@]}" # "3"
echo "${bar[2]}" # "c c"
baz () {
eval "bar=(\"\${$1[@]}\")"
for item in "${bar[@]}"
do
echo "$item"
done
# a
# b
# c c
}
baz isn't declaring bar local, so it's actually modifying the global variable bar, rather than scoping that to your function.$1 you pass in is the name of the variable -- a reference -- not its values.function baz {
set $1[@]
printf '%s\n' "${!1}"
}
foo=(a b 'c c')
bar=("${foo[@]}")
baz bar
eval? (Why do you think you needevalto accomplish that thing?)baz "${foo[@]}"is the accepted and conventional way to pass an array by value, which makes your values accessible as"$@"inside the function. What you're actually doing is not passing by value at all, but passing the name -- which is to say, passing by reference.evalinvolved.baz "${foo[@]}"correctly, it means no other arguments can be passed to the function?