I'm using jq
to parse a JSON file, extracting each JSON array in a series into a shell array.
My current code looks like the following:
for ((i = 0; i < ${#nvars[@]}; i++)); do
v1=($(cat $INPUT | jq '."config"[i]."var1"[]'))
echo $v1
done
error message:
error: i is not defined
I also replaced
v1=($(cat $INPUT | jq '."config"[i]."var1"[]'))
with
v1=($(cat $INPUT | jq '."config"[$i]."var1"[]'))
still not working. Any idea? Any help is appreciated!
Edit: Sample Input Data
{
"config-vars":[
{
"var1":["v1","v2"],
"var2":""
},
{
"var1":["v3",""],
"var2":"v4"
}
]
}
Best Answer
There's a fair bit of room for improvement. Let's start here:
...first, you don't actually need to use
cat
; it's slowing your performance, because it forcesjq
to read from a pipe rather than from your input file directly. Just runningjq <"$INPUT"
would be more robust (or, better,<"$input"
, to avoid using all-uppercase names, which are reserved by convention for shell builtins and environment variables).Second, you need to quote all variable expansions, including the expansion of the input file's name -- otherwise, you'll get bugs whenever your filename contains spaces.
Third,
array=( $(stuff) )
splits the output ofstuff
on all characters in IFS, and expands the results of that splitting as a series of glob expressions (so if the output contains*.txt
, and you're running this script in a directory that contains text files, you get the names of those files in your result array). Splitting on newlines only would mean you could correctly parse multi-word strings, and disabling glob expansion is necessary before you can use this technique reliably in the presence of glob characters. One way to do this is to setIFS=$'\n'
and runset -h
before running this command; another is to redirect the output of your command into awhile read
loop (shown below).Fourth, string substitution into code is bad practice in any language -- that way lies (local equivalents to) Bobby Tables, allowing someone who's supposed to be able to only change the data passed into your process to provide content which is processed as executable code (albeit, in this case, as a
jq
script, which is less dangerous than arbitrary code execution in a more full-featured language; still, this can allow extra data to be added to the output).Next, once you're getting
jq
to emit newline-separated content, you don't need to read it into an array at all: You can iterate over the content as it's written fromjq
and read into your shell, thus preventing the shell from needing to allocate memory to buffer that content:Finally -- let's say you do want to work with an array. There are two ways to do this that avoid pitfalls. One is to set
IFS
explicitly and disable glob expansion before the assignment:The other is to assign to your array with a loop:
...or, as suggested by @JohnKugelman, to use
read -a
to read the whole array in one operation: