to get output from a ssh for a for loop

Question

I need to get result of which process is using most swap space on a remote server. I am using below command which works fine if I log on to remote and run it, but it gives no output if I run it by using ssh to remote. I need to use ssh as I'll be doing this for multiple servers in a script

ssh someserver "for file in /proc/*/status; do awk '/VmSwap|Name/{printf $2 " " $3} END{print ""}' $file; done | sort -k 2 -n -r | head -1 | awk '{print $1}'"

I also tried using suggestions from previous questions on ths portal to enclose complete command in single quotes and awk in double quotes but that errors out for me as the double quote in printf statement is interpreted as closing of outer double quote of awk.

Answer 1

The problem is the quoting.

Use echo instead of ssh to see what would be transmitted to the ssh server:

$ echo "for file in /proc/*/status; do awk '/VmSwap|Name/{printf $2 " " $3} END{print ""}' $file; done | sort -k 2 -n -r | head -1 | awk '{print $1}'"
for file in /proc/*/status; do awk '/VmSwap|Name/{printf    } END{print }' ; done | sort -k 2 -n -r | head -1 | awk '{print }'

You see that the shell expands $1, $2 and $3. In an interactive shell, these are most likely empty strings. It might be enough to replace $ with \$, I didn't test it.

In general I prefer to send the commands on stdin, obviously this doesn't work if you need stdin. An additional advantage is that you can format it on multiple lines.

cat << 'EOF' |
for file in /proc/*/status; do
  awk '/VmSwap|Name/{printf $2 " " $3} END{print ""}' $file
done | sort -k 2 -n -r | head -1 | awk '{print $1}'
EOF
ssh someserver /bin/sh