bash check if a command succeeds from variable

Question

I usually check if a command succeeds or time out like this, which works just fine;

if timeout 30 someCommand; then
    echo "we're good"
else
    echo "command either failed or timed out"
fi

But with my new script which works with loops and variables, this simply doesn't work as expected;

wallets=/usr/local/bin/*-cli

for i in $wallets; do
    current_blocks=$(timeout 30 $i getblockcount)

    if $current_blocks; then
        echo "we're good"
    else
        echo "command either failed or timed out"
    fi
done

how can I fix this?

with $( ..) you are storing the output to some variable not the return code — P....
– P...., Commented Feb 20, 2019 at 17:19
Immediately after current_blocks=$(timeout 30 $i getblockcount) you can do currentBlocksRetCode=$? to get the return code, then if [[ $currentBlocksRetcode -eq 0 ]] then you are good. — marekful
– marekful, Commented Feb 20, 2019 at 17:19
@PS. I thought it's the same as putting the command between code quotes. @marekful this way it always returns we're good even if the command fails or time outs. — Marry Jane
– Marry Jane, Commented Feb 20, 2019 at 17:22

that other guy · Accepted Answer · 2019-02-20 17:20:05Z

2

The status of the previous command is available as $?:

wallets=/usr/local/bin/*-cli

for i in $wallets; do
    current_blocks=$(timeout 30 "$i" getblockcount)
    status=$?

    if [ "$status" -eq 0 ]; then
        echo "we're good"
    else
        echo "command either failed or timed out"
    fi
done

Or you can check the status directly:

if current_blocks=$(timeout 30 "$i" getblockcount)
then
  echo "It's good and the result is $current_blocks"
fi

answered Feb 20, 2019 at 17:20

that other guy

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1 Comment

Konrad Rudolph Over a year ago

Never mind, my mistake. I’d put quotes around the subshell invocations but they are not required.

aks · Accepted Answer · 2019-02-20 17:26:34Z

1

Assuming that the normal result of $(timeout 30 $i getblockcount) is a bunch of JSON, you'll need to use more quotes in order to capture the string and then test it for non-emptiness.

The code fragment should look something like this:

  current_blocks="$(timeout 30 $i getblockcount)"

  if [[ -n "$current_blocks" ]]; then
    echo "we're good"
  else
    echo "Command failed or timed out"
  fi

Alternatively, if you only want to check the return status of the command, you can check the $? variable. However, when using timeout with a command, the result status can be either the command status, or 124 from a timeout. If the command does not manage status returns very well, testing for a consistent status might be challenging -- unless you simply want to test for a zero (success) status.

In which case, the code fragment might look like:

  current_blocks="$(timeout 30 $i getblockcount)"

  if (( $? == 0 )); then
    echo "we're good"
  else
    echo "Command failed or timed out"
  fi

edited Feb 20, 2019 at 17:26

answered Feb 20, 2019 at 17:21

aks

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2 Comments

Marry Jane Over a year ago

It just returns a number on its own and nothing else.

aks Over a year ago

You'll still need to use [[ -n $current_blocks ]] to test if the value of current_blocks is empty or not. [[ $current_blocks ]] can also work, but relies on the variable value being syntactically "safe".

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