^ syntax error in awk when called via ssh

Question

I'm running filesystem usage command to detect /var filesystem usage beyond 80% from one host to multiple remote hosts.

My command runs fine (df -h /var | awk '$1 > 80'), but with ssh it gives me syntax errors.

for i in `cat /etc/gridhosts`; do ssh -n -o BatchMode=yes ${i} "df -h /var | awk '$4 > 80'" ; done
awk:  > 80
awk:  ^ syntax error
awk:  > 80
awk:  ^ syntax error
awk:  > 80

Answer 1

The issue is that $4 in the awk program is part of a double quoted string. Since it is in double quotes, the (local) shell will expand it before calling ssh.

In the shell, $4 is the 4th positional parameter, which most likely is empty. The means that the $4 in the awk code will be replaced by an empty string, producing an invalid awk program.

In this case, there is no need to run the awk command on the remote host. Instead, just do

while IFS= read -r remote; do
    ssh -n -o BatchMode=yes "$remote" 'df /var' | awk 'FNR == 2 && $5 > 80'
done </etc/gridhosts

Note that I've changed the awk code to look at $5 on line 2 rather than at $4 on every line, as this is where the the percentage is usually located. Also, I've removed the -h option for df as it's not needed, and I've made the loop read the input file line by line rather than expanding the full contents of the file in a for loop header (which is inelegant, and could, in the general case, eat a lot of memory unnecessarily).

You may also be interested in evaluating Ansible or similar software, as this would make doing cluster-wide operations much easier.