Bash: Breaking out of IF loop in FOR loop

Question

I am trying to combine a FOR loop (that iterates over IP addresses) and an IF loop (that uses nc to check for a successful ssh connection before moving on).

I have an array ${INSTANCE_IPS[@]} with the IP addresses in it (at the moment it contains 2 IP Addresses). Here is the code:

while [ $ITERATION -le 30 ]
do
    for instance in ${INSTANCE_IPS[@]}
    do    
        nc -w 2 $instance 22 > /dev/null
            if [ $? -eq 0 ]
            then echo "connection succeeded to $instance"
            else
                ITERATION=$((ITERATION+1))
                echo ITERATION=$ITERATION
                echo "[info] connection to $instance unsuccessful. trying again. iteration=$ITERATION"
                sleep 20
            fi
    done
done

The 'else' statement in the IF loop works fine. It is the 'then' statement I am having problems with... I don't know how to break out of the IF loop once the connections are successful. Here's an example output when I run the above:

connection succeeded to 10.11.143.171
connection succeeded to 10.11.143.170
connection succeeded to 10.11.143.171
connection succeeded to 10.11.143.170
connection succeeded to 10.11.143.171
connection succeeded to 10.11.143.170

If I use break after then echo "connection succeeded to $instance then it only iterates through 1 IP address and never breaks out:

connection succeeded to 10.11.143.171
connection succeeded to 10.11.143.171
connection succeeded to 10.11.143.171

Ideally I think the best thing to do would be to query the number of elements in the array, then perform a netcat connection an increment some value by 1 until it equals the number of elements in the array, but I'm really not sure how to dot that.

Any help is appreciated :) Please let me know if you need any more information.

Cheers

do you want to break both loops - stop as soon as you find one working? If so you could set $ITERATION to 30 and then call break — Jerry Jeremiah
– Jerry Jeremiah, Commented Apr 23, 2014 at 1:35
By "IF loop" I assume you mean "IP loop"? But maybe you don't. There's no such thing as an "if loop". — ooga
– ooga, Commented Apr 23, 2014 at 1:36
@ Jerry - So I want to make sure a successful ssh connection is made to all elements (IP addresses) in the array. So if there's 2 IP addresses I want to make sure that two successful connections (one to each IP address) is made before exiting the for loop and continuing on with the bash script — user3558925
– user3558925, Commented Apr 23, 2014 at 1:39
@ ooga - Nah I just meant "IF". Sorry I for the terminology wrong. I just meant I am nesting IF in a FOR loop. — user3558925
– user3558925, Commented Apr 23, 2014 at 1:40

that other guy · Accepted Answer · 2014-04-23 01:43:20Z

6

Reformulate your logic. You can't break if something succeeds, because you don't know whether another item might fail.

Instead, keep a flag saying whether you've successfully gone through all of them, and set it to false if something fails. At this point, you can also break and wait.

ITERATION=0
all_succeeded=false
while [ "$all_succeeded" = "false" -a $ITERATION -le 30 ]
do
    all_succeeded=true
    for instance in ${INSTANCE_IPS[@]}
    do    
        nc -w 2 $instance 22 > /dev/null
        if [ $? -eq 0 ]
        then 
          echo "connection succeeded to $instance"
        else
          all_succeeded=false
          echo "[info] connection to $instance unsuccessful."
          sleep 20
          break
        fi
    done
    let ITERATION++
done

if [ "$all_succeeded" = "true" ]
then
  echo "It worked"
else
  echo "Giving up"
fi

answered Apr 23, 2014 at 1:43

that other guy

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