Using Command Arguments and the $in Variable in Nushell Pipelines

# => │ 0 │ 6585 │ 6584 │ nu │ Running │ 0.00 │ 31.9 MiB │ 1.2 GiB │ # => ╰───┴──────┴──────┴──────┴─────────┴──────┴──────────┴─────────╯ ``` ::: tip Remember above, where the `size` column from the `ls` command was a `filesize`? Here, `status` is really just a string, and you can use all the normal string operations and commands with it, including (as above) the `==` comparison. You can examine the types for the table's columns using: ```nu ps | describe # => table<pid: int, ppid: int, name: string, status: string, cpu: float, mem: filesize, virtual: filesize> (stream) ``` The [`describe` command](/commands/docs/describe.md) can be used to display the output type of any command or expression. ::: ## Command Arguments in a Pipeline Sometimes, a command takes an _argument_ instead of pipeline _input_. For this scenario, Nushell provides the [`$in` variable](./pipelines.md#pipeline-input-and-the-special-in-variable) that let's you use the previous command's output in variable-form. For example: ```nu:line-numbers ls | sort-by size | reverse | first | get name | cp $in ~ ``` ::: tip Nushell Design Note Whenever possible, Nushell commands are designed to act on pipeline _input_. However, some commands, like `cp` in this example, have two (or more) arguments with different meanings. In this case, `cp` needs to know both the path to _copy_ as well as the _target_ path. As a result, this command is more ergonomic with two _positional parameters_. ::: ::: tip Nushell commands can extend across multiple lines for readability. The above is the same as: ```nu ls | sort-by size | reverse | first | get name | cp $in ~ ``` See Also: [Multi-line Editing](./line_editor.md#multi-line-editing) ::: The first three lines are the same commands we used in the second example above, so let's examine the last three: 4. The [`first` command](/commands/docs/first.md) simply returns the first value from the table. In this case, that means the file with the largest size. That's the `Cargo.lock` file if using the directory listing from the second example above. This "file" is a [`record`](./types_of_data.md#records) from the table which still contains its `name`, `type`, `size`, and `modified` columns/fields. 5. `get name` returns the _value_ of the `name` field from the previous command, so `"Cargo.lock"` (a string). This is also a simple example of a [`cell-path`](./types_of_data.md#cell-paths) that can be used to navigate and isolate structured data. 6. The last line uses the `$in` variable to reference the output of line 5. The result is a command that says _"Copy 'Cargo.lock' to the home directory"_ ::: tip [`get`](/commands/docs/get.md) and its counterpart [`select`](/commands/docs/select.md) are two of the most used filters in Nushell, but it might not be easy to

This section explains how to use command arguments in Nushell pipelines with the `$in` variable when a command requires arguments instead of pipeline input. It demonstrates an example that copies the largest file from a directory to the home directory, showcasing the use of `ls`, `sort-by`, `reverse`, `first`, `get`, and `cp` commands in conjunction with `$in`. It clarifies that `cp` needs positional parameters, so it is more ergonomic using `$in`.