Run a default command when xargs input is empty

Question

the title is quite self explanatory. I'm am writing a bash script that will manage all my packages (update, upgrade every upgrade-able apt and flatpak packages as well as removing the unneeded ones.

In one of the lines I'm using xargs to automatically run the upgrade command on every upgrade-able package without having to do a while loop. I'd like to echo a simple "No packages to upgrade" in the case where there's none.

I have tried this line but it didn't work

apt-get -s --no-download upgrade -V | grep '=>' | awk '{print $1}' | { sudo xargs --no-run-if-empty apt-get --only-upgrade upgrade -y } || { echo "No package to upgrade" }

Is there a way to run a "default" command in the case where xargs is empty ?

score 1 · Answer 1 · answered Dec 16 '22 at 18:50

You can create a function like this

if_not_empty() {
    read -r -t 1 line
    if [[ -z "$line" ]]; then
        echo "$1" >&2
        echo "empty"
        exit 0
    fi

    echo "$line"
    exec cat -
}

and then include it in your pipeline

mycommand | if_not_empty "No packages to upgrade" | xargs -E empty <other-xargs-args...>

Run a default command when xargs input is empty

1 Answers1