Linux string manipulation to make two parameters from one

Question

I'm receiving a list of operating systems, one per line, such as:

alpine/3.13
alpine/edge
alt/Sisyphus
alt/p9
apertis/v2019.5

I need to massage each line into two parameters to yield:

lxc launch images:alpine/3.13 alpine-3-13
lxc launch images:alpine/edge alpine-edge
lxc launch images:alt/Sisyphus alt-Sisyphus
lxc launch images:alt/p9 alt-p9
lxc launch images:apertis/v2019.5 apertis-v2019-5

and then run those commands. Note the second parameter has had everything non-alphanumeric switched to hyphens. I came up with the following:

echo alpine/3.13 | sed 'h;s#[/.]#-#g;x;G;s/\n/ /' | xargs -ti lxc launch images:{}

Unfortunately, although the command that xargs runs looks correct, instead of passing two arguments to lxc, xargs passes the entire thing as a single argument, so lxc tries to download an image named "alpine/3.13 alpine-3-13", instead of downloading the image named alpine/3.13 and using it to create a container named alpine-3-13.

Is there a way to pass lxc two separate arguments?

Example output:

# echo alpine/3.13 | sed 'h;s#[/.]#-#g;x;G;s/\n/ /' | xargs -ti lxc launch images:{}
lxc launch images:alpine/3.13 alpine-3-13
Creating the instance
Error: Failed instance creation: The requested image couldn't be found
# lxc launch images:alpine/3.13 alpine-3-13
Creating alpine-3-13
Starting alpine-3-13
<works correctly>

Complete (working) final command based on below input from KamilCuk and markp-fuso:

lxc image list images: | grep -v cloud | grep -Po '^\| \K[^ ]+(?=.+x86_64.+CONTAINER)' | sed 'h;s#[^[:alnum:]]#-#g;x;G;s/\n/ /;s/^ */images:/' | xargs -n2 lxc launch

`that runs looks correct` how can that `sed` "look" correct? — KamilCuk, Apr 27 '21 at 20:11
The t param to xargs tells it to output what it is about to run. It says it is going to run "lxc launch images:alpine/3.13 alpine-3-13", which works fine when pasted to a bash prompt. — Pascal, Apr 27 '21 at 20:14

KamilCuk · Answer 1 · 2021-04-27T20:18:49.850

Looks over-complicated - you do not need to use hold space at all. For remembering stuff from pattern and shuffling it use backreferences. Just:

echo alpine/3.13 | sed 's#\(.*\)/\(.*\)#lxc launch images:& \1-\2#'

You could run like:

echo alpine/3.13 | sed 's#\(.*\)/\(.*\)#images:& \1-\2#' | xargs -n2 lxc launch

or just:

eval "$(echo alpine/3.13 | sed 's#\(.*\)/\(.*\)#lxc launch images:& \1-\2#')"

But I would go with proper code anyway.

func() {
  arg=${1//\//-}
  lxc launch images:"$1" "$arg"
}
while IFS= read -r line; do
     func "$line"
done <<EOF
alpine/3.13 
EOF

or with same function:

export -f func
echo alpine/3.13 | xargs -d '\n' -n1 bash -c 'func "$@"' _

Is there a way to pass lxc two separate arguments?

Yes, but xargs has to know what to do with it. You can't "glue" two arguments with something in xargs - -i grabs only one argument. You could glue the images: in sed and then pass it, using your sed hold space shuffling, it's:

echo alpine/3.13 | sed 'h;s#[/.]#-#g;x;G;s/\n/ /;s/^ */images:/' | xargs -t -n2 lxc launch

but I see no value in xargs here at all anyway.

Your first example displays a command but doesn't actually run it. Most of your examples do not replace all the non-alphanumeric characters.in the second parameter (currently that is only slashes and periods). Your last example does appear to work! Thank you! — Pascal, Apr 27 '21 at 20:42

markp-fuso · Answer 2 · 2021-04-27T22:17:24.440

OP's examples start with echo <operating_system_string> which I'm going to assume implies the input file (full of <operating_systen_string>'s) is being passed through some sort of loop, and upon each pass through the loop a variable is being assigned the current <operating_system_string>.

Key point here is that a variable is going to be used to hold the current <operating_system_string>.

I'm wondering if OP can use parameter substitution to accomplish the desired task, eg:

$ osname='alpine/3.13'
$ echo "${osname//[^[:alnum:]]/-}"     # replace all non-alphanumerics with a '-'
alpine-3-13

So making the lxc call would look like:

$ echo lxc launch images:"${osname}" "${osname//[^[:alnum:]]/-}"
lxc launch images:alpine/3.13 alpine-3-13

$ lxc launch images:"${osname}" "${osname//[^[:alnum:]]/-}"

Taking a run at the list of OS names ...

Input file:

$ cat oslist
alpine/3.13
alpine/edge
alt/Sisyphus
alt/p9
apertis/v2019.5

Running the file through a while loop:

while read -r osname
do
    echo lxc launch images:"${osname}" "${osname//[^[:alnum:]]/-}"
done < oslist

Which generates:

lxc launch images:alpine/3.13 alpine-3-13
lxc launch images:alpine/edge alpine-edge
lxc launch images:alt/Sisyphus alt-Sisyphus
lxc launch images:alt/p9 alt-p9
lxc launch images:apertis/v2019.5 apertis-v2019-5

Once OP is satisfied with the results the echo could be removed to instead invoke the lxc call on each pass through the loop.

Linux string manipulation to make two parameters from one

2 Answers2