how to verify at least XG free space on /var

Question

we have the following df -h output

[root@trump var]# df -h | grep "/var"

/dev/mapper/vg-lvm_var   101G   85G   17G  84% /var

how to verify at least 10G free space on /var in bash/awk/perl one liner

meanwhile I write this syntax :

[[ ` df -h | grep "/var" | awk '{print $4}' | sed s'/G//g' ` -lt 10 ]] && echo "/var need at least 10G"

but this syntax isn't elegant and ugly and maybe I missed some rules

Answer 1

With a new enough GNU df, you could extract just the available space using the --output option. And you could the rest of the comparison with awk:

$ df -k --output=avail /var | awk 'NR == 2 && ($1 < 10*2**20) {print "/var need at least 10G"}'
/var need at least 10G

Even without that, if you wanted to get a specific filesystem, it's best to do df /var instead of df | grep /var (unless you want to catch the case of nothing being mounted on /var).

For running other commands based on this, with bash, use the (( )) arithmetic context:

if (( $(df -k --output=avail /var | tail -1) < 10*2**20 ))
then
    log "/var need at least 10G"
fi