4 ms·

Am I the only one completely confused by the examples that appear to put command line arguments after shell end-of-line comments? Is that not a typical shell?

Am I the only one completely confused by the examples that appear to put command line arguments after shell end-of-line comments? Is that not a typical shell? example: nix run .#cowsay -- flakes are neat Some explanation of what the heck this means would be really useful.

dvdkon 3y ago
"--" isn't anything special in a typical shell. It's just another argument, one that customarily means "pass the rest of arguments on to a subprocess". Or are you confused about the "#"? It doesn't start a comment in the middle of a token.
- heleninboodler 3y ago
  It was the "#". I didn't realize that about the behavior in the middle of a token, and apparently the syntax colorizer doesn't either.
- Izkata 3y ago
  > one that customarily means "pass the rest of arguments on to a subprocess". It's convenient for passing options and args to a subprocess, but it customarily means "don't interpret anything following this as a short or long option, just as a positional argument". For example: touch -f # error touch -- -f # creates a file named "-f" rm * # oh crap we just passed "rm -f" a bunch of files rm -- * # don't treat that "-f" as an option, just delete the file named "-f"
femiagbabiaka 3y ago
https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap12.html#tag_12_02 https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1... The first -- argument that is not an option-argument should be accepted as a delimiter indicating the end of options. Any following arguments should be treated as operands, even if they begin with the '-' character.
pushtheenvelope 3y ago
yikes! thanks for pointing that out. The blog's renderer is confused too and renders the `#cowsay -- flakes are neat` as a comment. To explain what's happening: - The example above is running `nix run <flake output attribute> -- <arguments to pass to the flake output's binary>`. - The `<flake output attribute>` here is `.#cowsay`, which is to be read as: `<flake reference>#<attribute path>`. The # is a separator here. - The `<flake reference>` being `.` implies its a local flake at the current directory. The `<attribute path>` in this case is the output from the flake i.e. the `cowsay` program. further fun to be found at: https://nixos.org/manual/nix/stable/command-ref/new-cli/nix.html#flake-output-attribute https://nixos.org/manual/nix/stable/command-ref/new-cli/nix.... As a meta-comment, yeah, this is kinda non-trivial for most of us. This is why we build devbox which provides a more familiar UX like `devbox add cowsay && devbox run -- cowsay "flakes are neat"`
tripdout 3y ago
It's nix run, the dot means current directory, # means flake, cowsay is the attribute, and then anything after -- is passed to what's run by that command, which is typical of many Unix programs. So it's run the cowsay attribute from the flake in the current directory, passing flakes are neat as input to cowsay.
pxc 3y ago
The comment syntax for most (virtually all?) shells actually doesn't start with a pound sign but with the word boundary or whitespace preceding the pound sign. You can have unescaped pound signs within tokens in shell languages, and thus they are used (perhaps unfortunately) as delimiters in the current flake URI schema.

dvdkon 3y ago

"--" isn't anything special in a typical shell. It's just another argument, one that customarily means "pass the rest of arguments on to a subprocess". Or are you confused about the "#"? It doesn't start a comment in the middle of a token.

heleninboodler 3y ago
It was the "#". I didn't realize that about the behavior in the middle of a token, and apparently the syntax colorizer doesn't either.
Izkata 3y ago
> one that customarily means "pass the rest of arguments on to a subprocess". It's convenient for passing options and args to a subprocess, but it customarily means "don't interpret anything following this as a short or long option, just as a positional argument". For example: touch -f # error touch -- -f # creates a file named "-f" rm * # oh crap we just passed "rm -f" a bunch of files rm -- * # don't treat that "-f" as an option, just delete the file named "-f"

femiagbabiaka 3y ago

https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap12.html#tag_12_02 https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1... The first -- argument that is not an option-argument should be accepted as a delimiter indicating the end of options. Any following arguments should be treated as operands, even if they begin with the '-' character.

pushtheenvelope 3y ago

yikes! thanks for pointing that out. The blog's renderer is confused too and renders the `#cowsay -- flakes are neat` as a comment. To explain what's happening: - The example above is running `nix run <flake output attribute> -- <arguments to pass to the flake output's binary>`. - The `<flake output attribute>` here is `.#cowsay`, which is to be read as: `<flake reference>#<attribute path>`. The # is a separator here. - The `<flake reference>` being `.` implies its a local flake at the current directory. The `<attribute path>` in this case is the output from the flake i.e. the `cowsay` program. further fun to be found at: https://nixos.org/manual/nix/stable/command-ref/new-cli/nix.html#flake-output-attribute https://nixos.org/manual/nix/stable/command-ref/new-cli/nix.... As a meta-comment, yeah, this is kinda non-trivial for most of us. This is why we build devbox which provides a more familiar UX like `devbox add cowsay && devbox run -- cowsay "flakes are neat"`

tripdout 3y ago

It's nix run, the dot means current directory, # means flake, cowsay is the attribute, and then anything after -- is passed to what's run by that command, which is typical of many Unix programs. So it's run the cowsay attribute from the flake in the current directory, passing flakes are neat as input to cowsay.

pxc 3y ago

The comment syntax for most (virtually all?) shells actually doesn't start with a pound sign but with the word boundary or whitespace preceding the pound sign. You can have unescaped pound signs within tokens in shell languages, and thus they are used (perhaps unfortunately) as delimiters in the current flake URI schema.