How to format output linux script result - linux

Question

I have a project to execute a script and need to format the output, including unexpected errors. I know that I can use trap to intercept errors, so I tried to use it to format the output, the example is as follows
#!/bin/bash
set -o errtrace
status=false
trap "print " ERR
print() {
echo "{\"status\":$status,\"result\":\"$1\"}"
exit 0
}
main(){
arg=$1
if [ "$arg" == "0" ];then
status=true
print "successfully finish"
else
cat /a/b/c/d >>/dev/null
echo "abnormal termination"
fi
}
main "$#"
The logic of success meets my needs as follows
# bash format-print.sh 0
{"status":true,"result":"successfully finish"}
But when an exception error is caught it doesn't meet my needs
# bash format-print.sh 1
cat: /a/b/c/d: No such file or directory
{"status":false,"result":""}
I would like to enter the following result
# bash format-print.sh 1
cat: /a/b/c/d: No such file or directory
{"status":false,"result":"cat: /a/b/c/d: No such file or directory"}
How can I modify the code to meet my needs, and if trap does not work or is not the standard way, can you please tell me how to implement it?

Answer 1

It sounds like what you need is to capture the error output from your command so that you can include it in your formatted output. You don't need a trap for this, although if you wanted to use a trap to invoke print you could do that (maybe with EXIT instead of ERR though).
With direct calls to the print function, this will do what you're looking for:
#!/bin/bash
set -o errtrace
status=false
#trap "print " ERR # removed trap for testing
print() {
echo "{\"status\":$status,\"result\":\"$1\"}"
exit 0
}
main(){
arg=$1
if [ "$arg" == "0" ];then
status=true
print "successfully finish"
else
# captures stderr into a variable while discarding stdout
result=$( cat /a/b/c/d 2>&1 >/dev/null )
print "$result"
fi
}
main "$#"
This will provide the output:
$ ./test.sh 1
{"status":false,"result":"cat: /a/b/c/d: No such file or directory"}