Shell Programming and Scripting

you dont use df commands output with file. df command is disk fragment (can only be used with the directory.)
bdf - block disk fragment (can only be used with directory.)

i think i wrongly understood your question. i thought what you were asking is .. in which directory your file is present show the disk usage. this is what the above command will do.
if your requirement is something else. please let me know and sorry for misunderstanding.

I think everyone is confused, i asked simple question that i have file, and i need to check first line and last line to calculate its usage size, if its 90% >= then i got email on someid.