How not to interrupt the execution of the loop in case of errors and write them to a variable?

Question

I want to backup mikrotiks via scp. This script loops through the hosts from the hosts.txt. One by one, connects to each device from the list. Does backup and all manipulations. If at some stage it was not possible to connect to the device, then an empty backup is formed, which is then sent to the cloud. I want to check. If it was not possible to connect to the host, then write this host into a variable, line by line, and go to the next device. Next, I will notify about all failed connections. The problem is that only the first error is written to the variable, all subsequent ones are ignored. Tell me who knows what.

#!/bin/bash
readarray -t hosts < hosts.txt

DATE=$(date +'%Y-%m-%d_%H-%M-%S')
ROS='<br>'
ERR=( )

 #Get values from main list
for host in ${hosts[*]}
do
    #Get values from sub list
    hostname=($(echo ${host} | tr "_" " "))
    echo ${hostname[0]} - ${hostname[1]}
    #connect & backup & transfer & archive & rm old files & moove to cloud
    if ssh backup@${hostname[0]} -C "/system backup save name=${hostname[1]}_$DATE"; then
        scp backup@${hostname[0]}:"${hostname[1]}_$DATE.backup" ./
        ssh backup@${hostname[0]} -C "rm ${hostname[1]}_$DATE.backup"
        tar -czvf ./${hostname[1]}_$DATE.tar.gz ${hostname[1]}_$DATE.backup
        scp ./${hostname[1]}_$DATE.tar.gz my@cloud.com:/var/www/my.cloud.com/backups/mikrotik/
        rm ${hostname[1]}_$DATE.backup ${hostname[1]}_$DATE.tar.gz
        ROS=$ROS${hostname[1]}"<br>"
    else
        ERR+=(${hosts[*]} "is not ready")
    fi
done

---

hosts.txt
10.10.8.11_CAP-1
10.10.9.12_CAP-2
10.10.10.13_CAP-3

Answer 1

As I noted in the comments, you're misusing the array notation. Your line ERR=(${hosts[*]} "is not ready") should be ERR+=(${hosts[*]} "is not ready") and you should define ERR as an array, not a scalar: ERR=( ) for example, or declare -a ERR. Similarly with ROS.

Here's a test script that avoids all the ssh and scp work to demonstrate that lists of passing and failing hosts work — that the arrays hosts, ROS and ERR are handled correctly.

Note the use of "${ERR[@]}" with double quotes and @ instead of no quotes and *. The difference matters because the values in the array contain spaces. Try the alternatives. Note, too, that printf always prints, even when there is no argument corresponding to the %s in the format string. Hence the check on the number of elements in the array before invoking printf.

#!/bin/bash
# Needs Bash 4.x - Bash 3.2 as found on Macs does not support readarray

# readarray -t hosts < hosts.txt
hosts=( passed-1 failed-2 passed-3 failed-4 passed-5 )

declare -a ERR
declare -a ROS
status=passed
for host in "${hosts[@]}"
do
    if [ "$status" = "passed" ]
    then ROS+=( "$host $status" ); status="failed"
    else ERR+=( "$host $status" ); status="passed"
    fi
done

# Brute force but handles empty lists
for passed in "${ROS[@]}"
do printf "== PASS == [%s]\n" "$passed"
done
for failed in "${ERR[@]}"
do printf "!! FAIL !! [%s]\n" "$failed"
done

# Alternative - better spread over multiple lines each
if [ "${#ROS}" -gt 0 ]; then printf "== PASS == [%s]\n" "${ROS[@]}"; fi
if [ "${#ERR}" -gt 0 ]; then printf "!! FAIL !! [%s]\n" "${ERR[@]}"; fi

Output:

== PASS == [passed-1 passed]
== PASS == [passed-3 passed]
== PASS == [passed-5 passed]
!! FAIL !! [failed-2 failed]
!! FAIL !! [failed-4 failed]
== PASS == [passed-1 passed]
== PASS == [passed-3 passed]
== PASS == [passed-5 passed]
!! FAIL !! [failed-2 failed]
!! FAIL !! [failed-4 failed]

I'm sorry there are so many failures to backup your data!