Even if you need something just once, just install it and then uninstall it, takes like 10 seconds.
apt install foo && apt remove foo
That’s essentially what nix-shell -p does. Not a special feature of nix, just nix’s way of doing the above.
Actually using it though is pretty convenient; it disappears on its own when I exit the shell. I used it just the other day with nix-shell -p ventoy to install ventoy onto an ssd, I may not need that program again for years. Just used it with audible-cli to download my library and strip the DRM with ffmpeg. Probably won’t be needing that for a while either.
The other thing to keep in mind is that since Nix is meant to be declarative, everything goes in a config file, which screams semi-permenant. Having to do that with ventoy and audible-cli would just be pretty inconvenient. That’s why it exists; due to how Nix is, you need a subcommand for temporary one-off operations.
Here’s one I have saved in my shell aliases.
nscript() { local name="${1:-nscript-$(printf '%s' $(echo "$RANDOM" | md5sum) | cut -c 1-10)}" echo -e "#!/usr/bin/env bash\n#set -Eeuxo pipefail\nset -e" > ./"$name".sh && chmod +x ./"$name".sh && hx ./"$name".sh } alias nsh='nscript'Admittedly much more complicated than necessary, but it’s pretty full featured. first line constructs a filename for the new script from a generated 10 character random hash and prepends “nscript” and a user provided name.
The second line writes out the shebang and a few oft used bash flags, makes the file executable and opens in in my editor (Helix in my case).
The third line is just a shortened alias for the function.