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
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}'A perfect example when to use 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
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.
Just a thumb of rule to make sense of it: A column in AWK is by default any space separated part. You can change the column separator to any other character too with
-F ":"in example would be a double colon. There is also a way to print all columns, but with certain exceptions. In example print all, but the third and fourth columns:ls -l | awk '{$3=""; $4=""; print $0}'. Admittely I forget this syntax often and have to look for it again.