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Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).

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Help with sed commands (lemmy.dbzer0.com)

submitted 3 weeks ago* (last edited 3 weeks ago) by [email protected] to c/[email protected]

19 comments fedilink hide all child comments

Hi all! I have always only used sed with s///, becouse I've never been able to figure out how to properly make use of its full capabilities. Right now, I'm trying to filter the output of df -h --output=avail,source to only get the available space from /dev/dm-2 (let's ignore that I just realized df accepts a device as parameter, which clearly solves my problem).

This is the command I'm using, which works:

df -h --output=avail,source \
    | grep /dev/dm-2 \
    | sed -E 's/^[[:blank:]]*([0-9]+(G|M|K)).*$/\1/

However, it makes use of grep, and I'd like to get rid of it. So I've tried with a combiantion of t, T, //d and some other stuff, but onestly the output I get makes no sense to me, and I can't figure out what I should do instead.

In short, my question is: given the following output

$ df -h --output=avail,source 
Avail Filesystem
  87G /dev/dm-2
 1.6G tmpfs
  61K efivarfs
  10M dev
...

How do I only get 87G using only sed as a filter?

EDIT:

Nevermind, I've figured it out...

$ df -h --output=avail,source \
    | sed -E 's/^[[:blank:]]*([0-9]+(G|M|K))[[:blank:]]+(\/dev\/dm-2).*$/\1/; t; /.*/d'
85G

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[–] [email protected] 8 points 3 weeks ago (1 children)

Are you opposed to using awk? Printing out a specific column is basically the only thing I actually know how to do with it: df -h --output=avail,source | awk '/dm-2/ {print $1}'

[–] [email protected] 2 points 3 weeks ago (1 children)

Are you opposed to using awk?

Not at all, I'm just not familiar with it so I find it confusing.

Although, looking at your command, i think I understand what it means

[–] [email protected] 1 points 3 weeks ago* (last edited 3 weeks ago)

I had to check the syntax because I also don't use it enough to be sure, definitely a bit weird. Basically just grep for a regex and print the specified column.