Base Command implementation for Format

Note that run is not implemented yet

crates/nu-command/src/default_context.rs

@@ -42,6 +42,7 @@ pub fn create_default_context() -> EngineState {
             External,
             First,
             For,
+            Format,
             From,
             FromJson,
             Get,

crates/nu-command/src/strings/format/format.rs

@@ -0,0 +1,53 @@
+//use nu_engine::CallExt;
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EngineState, Stack};
+use nu_protocol::{Example, PipelineData, ShellError, Signature, SyntaxShape};
+
+#[derive(Clone)]
+pub struct Format;
+
+impl Command for Format {
+    fn name(&self) -> &str {
+        "format"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("format").required(
+            "pattern",
+            SyntaxShape::String,
+            "the pattern to output. e.g.) \"{foo}: {bar}\"",
+        )
+    }
+
+    fn usage(&self) -> &str {
+        "Format columns into a string using a simple pattern."
+    }
+
+    fn run(
+        &self,
+        _engine_state: &EngineState,
+        _stack: &mut Stack,
+        _call: &Call,
+        _input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        todo!()
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            description: "Print filenames with their sizes",
+            example: "ls | format '{name}: {size}'",
+            result: None,
+        }]
+    }
+}
+
+#[cfg(test)]
+mod test {
+    #[test]
+    fn test_examples() {
+        use super::Format;
+        use crate::test_examples;
+        test_examples(Format {})
+    }
+}

crates/nu-command/src/strings/format/mod.rs

@@ -0,0 +1,3 @@
+pub mod format;
+
+pub use format::Format;

crates/nu-command/src/strings/mod.rs

@@ -1,7 +1,9 @@
 mod build_string;
+mod format;
 mod size;
 mod split;
 
 pub use build_string::BuildString;
+pub use format::*;
 pub use size::Size;
 pub use split::*;