I'm running this command do get a value from the json;
addr=$(./xuez-cli getnetworkinfo | jq -r '.localaddresses[0].address')
and it works just fine.
BUT if this .localaddresses[0].address part empty or doesn't even exist, jq sets the addr variable as null like this; addr=null
and I want to check if the json is empty/null and run some other command instead of parsing it as null string.
I couldn't find a way to work this around. How can I do this?
Something useful I found for shell scripts was:
jq '.foo // empty'
Which returns the match if successful, and the empty string if unsuccessful. So in bash I use:
addr=$(./xuez-cli getnetworkinfo | jq -r '.localaddresses[0].address // empty')
if [[ ! -z "$addr" ]]; then
# do something
fi
Ref: https://github.com/stedolan/jq/issues/354#issuecomment-43147898 https://unix.stackexchange.com/questions/451479/jq-print-for-null-values
First, a note: There's nothing inherently wrong with addr=null; you can just test for it:
if [[ $addr = null ]]; then ...code here...; fi
The rest of this answer pretends the above were untrue. :)
There are two practices that are notable as improving ease of error handling for this case:
set -o pipefail will detect whether any part -- not just the last component -- of a shell pipeline fails.jq -e will cause jq's exit status to reflect whether it returned content that was either false or null.Thus:
set -o pipefail
if addr=$(./xuez-cli getnetworkinfo | jq -er '.localaddresses[0].address'); then
: "address retrieved successfully; this message is not logged unless set -x is active"
else
echo "Running other logic here"
fi
...goes to Running other logic here if either jq fails (and -e specifies that false and null shall be treated as failures), or if xuez-cli reports an unsuccessful exit status.