How can I escape a command passed to bash via bash -c? - linux

Question

I would like to run the following command via docker -c:
for line in `docker ps | awk '{print $1}' | grep -v CONTAINER`; do docker ps | grep $line | awk '{printf $NF" "}' && echo $(( `cat /sys/fs/cgroup/memory/docker/$line*/memory.usage_in_bytes` / 1024 / 1024 ))MB ; done
How do I have to escape the command when passing it via -c? What symbols do I have to escape?
I tried various versions, including this one, which gives me the error unexpected EOF while looking for matching "
bash -c 'for line in \`docker ps | awk \'{print $1}\' | grep -v CONTAINER\`\; do docker ps | grep $line | awk \'{printf $NF\\" \\"}\' && echo $(( \`cat /sys/fs/cgroup/memory/docker/$line*/memory.usage_in_bytes\` / 1024 / 1024 ))MB \; done
Sidenote: The command gives you the memory consumption for each docker container.

Answer 1

I am guessing you are trying to divide the number of bytes.
In order to do arithmetic calculations you need to use expr.
Try this:
for line in `docker ps | awk '{print $1}' | grep -v CONTAINER`; do docker ps | grep $line | awk '{printf $NF" "}' && echo $(expr $( cat /sys/fs/cgroup/memory/docker/$line*/memory.usage_in_bytes) / 1024 / 1024 )MB ; done

Answer 2

Found the solution:
bash -c 'for line in $(docker ps | awk '"'"'{print $1}'"'"' | grep -v CONTAINER); do docker ps | grep $line | awk '"'"'{printf $NF" "}'"'"' && echo $(( $(cat /sys/fs/cgroup/memory/docker/$line*/memory.usage_in_bytes) / 1024 / 1024 ))MB ; done'
Can someone explain it to me?

Answer 3

IIUC, it's a good use case for Bash printf %q specifier. Save a line to a
file, say /tmp/DOCKER-COMMAND and then format it with printf %q:
$ printf "%q\n" "$(< /tmp/DOCKER-COMMAND)"
for\ line\ in\ \`docker\ ps\ \|\ awk\ \'\{print\ \$1\}\'\ \|\ grep\ -v\ CONTAINER\`\;\ do\ docker\ ps\ \|\ grep\ \$line\ \|\ awk\ \'\{printf\ \$NF\"\ \"\}\'\ \&\&\ echo\ \$\(\(\ \`cat\ /sys/fs/cgroup/memory/docker/\$line\*/memory.usage_in_bytes\`\ /\ 1024\ /\ 1024\ \)\)MB\ \;\ done
You can copy the output line and paste it literally to bash -c:
$ bash -c for\ line\ in\ \`docker\ ps\ \|\ awk\ \'\{print\ \$1\}\'\ \|\ grep\ -v\ CONTAINER\`\;\ do\ docker\ ps\ \|\ grep\ \$line\ \|\ awk\ \'\{printf\ \$NF\"\ \"\}\'\ \&\&\ echo\ \$\(\(\ \`cat\ /sys/fs/cgroup/memory/docker/\$line\*/memory.usage_in_bytes\`\ /\ 1024\ /\ 1024\ \)\)MB\ \;\ done
fervent_gates 2MB
youthful_wozniak 3MB

Answer 4

Does it need to fit in a single line? Using a quoted heredoc gets you out of most quoting trouble:
bash <<'END_BASH'
docker ps | {
read header
while read -ra fields; do
mem=$(< /sys/fs/cgroup/memory/docker/"${fields[0]}"*/memory.usage_in_bytes)
printf "%s %dMB\n" "${fields[-1]}" $((mem / 1024 / 1024))
done
}
END_BASH