(d+)%s*/$

# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/xvda             15997904   2404540  12943248  16% /
tmpfs                   252456         0    252456   0% /lib/init/rw
tmpfs                   252456        36    252420   1% /dev/shm

df | awk 'NR > 1 {print $5, $6;}'

65% /
1% /dev
1% /dev/shm

df | awk 'NR > 1 {print $5;}' | tr -d '%'

df | awk '//dev/shm$/ {print $5;}' | tr -d '%'

df | awk '//$/ {print $5;}' | tr -d '%'

df -h | egrep --only-matching '[[:digit:]]+%' | tr -d '%'

import subprocess
import re
print re.search('(d+)% /', subprocess.Popen(["df"], stdout=subprocess.PIPE).communicate()[0]).group(1)

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import subprocess
import re

p = subprocess.Popen(["df"], stdout=subprocess.PIPE)
for line in p.stdout:
    usage = re.search('(d+)% /', line.rstrip())
    if usage != None:
        print usage.group(1)

df --output=pcent,target