because AWK is it's own language as well as a program (awk), I'll add to ocicats post by noting the easiest way to get a specific column out of 'df' output with awk.
Code:
df | awk '{ print $1 }'
which will print the first column to standard output, $2 the second column, $3 the third column and so on.
Accessing the column(s) a line at a time is also easy as pie but I'll let you figure that out along with more useful things ;-)
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Thou shalt check the array bounds of all strings (indeed, all arrays), for surely where thou typest ``foo'' someone someday shall type ``supercalifragilisticexpialidocious''.