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I need to find amount of free disk space on a RAM disk in a portable script (not GUI, not anything distro-specific). The df utility does the job, but it spews quite a lot of output so I have to fish it out, like:

df -P /tmp | tail -n 1 | awk '{print $4; }'

Tried also stat but cannot figure how to specify a 'filesystem' to it. Even when tmpfs is mounted on /tmp, stat "%f" /tmp interprets /tmp as a file, not as a filesystem.

Is there a better way?

(No this is not a duplicate for 'how to find free disk space and analyze usage'. Thank you for being so vigilant)

  • The way you do it is the way to go. You've a oneliner that does what you need (with only 3 commands), not sure why you look for a shorten way. – Chen A. Jul 26 '17 at 14:33
  • Thanks @Vinny. I'm not expert in Unix, thought there's something obvious I'm missing. And would like to minimize dependency on other things (tail,awk). – ddbug Jul 26 '17 at 14:36
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    For the filesystem information on /tmp, use stat -f /tmp. You'd still need some massaging of the output if you want a single number. – user4556274 Jul 26 '17 at 14:37
  • A compatible way would be to use read -d '' -ra df_arr < <(LC_ALL=C df -P /tmp); echo "${df_arr[11]}" See mywiki.wooledge.org/BashFAQ/094?highlight=%28disk%29 – Valentin Bajrami Jul 26 '17 at 14:37
  • @ddbug I think your solution is good, simple and readable. You should stick to it. with stat -f /tmp you still need to do manipulations, stat -f /tmp | grep 'Free' | head -n 1 | awk '{ print $5 }'. Looks less efficient if you ask me – Chen A. Jul 26 '17 at 14:44
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From the man page for stat(1)

-f, --file-system
display file system status instead of file status

So to pull the free blocks of the filesystem on which /tmp is located, you could try something like

stat -f /tmp -c "%f"

Or, to get the value in octets, multiply free blocks by blocksize:

stat -f /tmp -c "%f*%S" | bc
  • Perfect! except that bc is not available on my system ,so echo $(( $(stat -f /tmp -c "%f*%S") )) – ddbug Jul 26 '17 at 15:33

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