This commit introduces a basic help feature. We can go to it

with the `help` command to explore and list all commands available.

Enter will also try to see if the location to be entered is an existing
Nu command, if it is it will let you inspect the command under `help`.

This provides baseline needed so we can iterate on it.

README.md

@@ -209,6 +209,7 @@ Nu adheres closely to a set of goals that make up its design philosophy. As feat
 | date (--utc) | Get the current datetime |
 | ps | View current processes |
 | sys | View information about the current system |
+| which filename | Finds a program file. |
 | open {filename or url} | Load a file into a cell, convert to table if possible (avoid by appending '--raw') |
 | post url body (--user <user>) (--password <password>) | Post content to a url and retrieve data as a table if possible |
 | rm   {file or directory} | Remove a file, (for removing directory append '--recursive') |
@@ -217,6 +218,8 @@ Nu adheres closely to a set of goals that make up its design philosophy. As feat
 | p | Go to previous shell |
 | n | Go to next shell |
 | shells | Display the list of current shells |
+| help | Display help information about commands |
+| version | Display Nu version |
 
 ## Filters on tables (structured data)
 | command | description |
@@ -230,8 +233,11 @@ Nu adheres closely to a set of goals that make up its design philosophy. As feat
 | add field value | Add a new field to the table |
 | sum | Sum a column of values |
 | edit field value | Edit an existing field to have a new value |
+| reverse | Reverses the table. |
 | skip amount | Skip a number of rows |
+| skip-while condition | Skips rows while the condition matches. |
 | first amount | Show only the first number of rows |
+| last amount | Show only the last number of rows |
 | nth row-number | Return only the selected row |
 | str (field) | Apply string function. Optional use the field of a table |
 | tags | Read the tags (metadata) for values |
@@ -240,13 +246,13 @@ Nu adheres closely to a set of goals that make up its design philosophy. As feat
 | to-json | Convert table into .json text |
 | to-toml | Convert table into .toml text |
 | to-yaml | Convert table into .yaml text |
+| to-bson | Convert table into .bson text |
 | to-csv  | Convert table into .csv text  |
 | to-bson | Convert table into .bson binary data |
 | to-tsv | Convert table into .tsv text |
 | to-sqlite | Convert table to sqlite .db binary data |
 | reverse | Reverse the rows of a table |
 
-
 ## Filters on text (unstructured data)
 | command | description |
 | ------------- | ------------- |
@@ -256,7 +262,7 @@ Nu adheres closely to a set of goals that make up its design philosophy. As feat
 | from-json | Parse text as .json and create table |
 | from-sqlite | Parse binary data as sqlite .db and create table |
 | from-toml | Parse text as .toml and create table |
-| from-tsv | Parse text as .tsv and create table |
+| from-tsv  | Parse text as .tsv and create table  |
 | from-xml | Parse text as .xml and create a table |
 | from-yaml | Parse text as a .yaml/.yml and create a table |
 | lines | Split single string into rows, one per line |

src/cli.rs

@@ -212,6 +212,7 @@ pub async fn cli() -> Result<(), Box<dyn Error>> {
             whole_stream_command(Config),
             whole_stream_command(SkipWhile),
             per_item_command(Enter),
+            per_item_command(Help),
             whole_stream_command(Exit),
             whole_stream_command(Autoview),
             per_item_command(Cpy),

src/commands.rs

@@ -25,6 +25,7 @@ pub(crate) mod from_tsv;
 pub(crate) mod from_xml;
 pub(crate) mod from_yaml;
 pub(crate) mod get;
+pub(crate) mod help;
 pub(crate) mod last;
 pub(crate) mod lines;
 pub(crate) mod ls;
@@ -91,6 +92,7 @@ pub(crate) use from_xml::FromXML;
 pub(crate) use from_yaml::FromYAML;
 pub(crate) use from_yaml::FromYML;
 pub(crate) use get::Get;
+pub(crate) use help::Help;
 pub(crate) use last::Last;
 pub(crate) use lines::Lines;
 pub(crate) use ls::LS;

src/commands/autoview.rs

@@ -12,6 +12,14 @@ impl WholeStreamCommand for Autoview {
         "autoview"
     }
 
+    fn signature(&self) -> Signature {
+        Signature::build("autoview")
+    }
+
+    fn usage(&self) -> &str {
+        "View the contents of the pipeline as a table or list."
+    }
+
     fn run(
         &self,
         args: CommandArgs,
@@ -19,10 +27,6 @@ impl WholeStreamCommand for Autoview {
     ) -> Result<OutputStream, ShellError> {
         Ok(args.process_raw(registry, autoview)?.run())
     }
-
-    fn signature(&self) -> Signature {
-        Signature::build("autoview")
-    }
 }
 
 pub fn autoview(

src/commands/cd.rs

@@ -5,6 +5,19 @@ use crate::prelude::*;
 pub struct CD;
 
 impl WholeStreamCommand for CD {
+    fn name(&self) -> &str {
+        "cd"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("cd")
+            .optional("directory", SyntaxType::Path)
+    }
+
+    fn usage(&self) -> &str {
+        "Change to a new path."
+    }
+
     fn run(
         &self,
         args: CommandArgs,
@@ -12,14 +25,6 @@ impl WholeStreamCommand for CD {
     ) -> Result<OutputStream, ShellError> {
         cd(args, registry)
     }
-
-    fn name(&self) -> &str {
-        "cd"
-    }
-
-    fn signature(&self) -> Signature {
-        Signature::build("cd").optional("directory", SyntaxType::Path)
-    }
 }
 
 fn cd(args: CommandArgs, registry: &CommandRegistry) -> Result<OutputStream, ShellError> {

src/commands/classified.rs

@@ -140,6 +140,29 @@ impl InternalCommand {
                         context.add_span_source(uuid, span_source);
                     }
                     CommandAction::Exit => std::process::exit(0),
+                    CommandAction::EnterHelpShell(value) => {
+                        match value {
+                            Tagged {
+                                item: Value::Primitive(Primitive::String(cmd)),
+                                ..
+                            } => {
+                                context.shell_manager.insert_at_current(Box::new(
+                                    HelpShell::for_command(
+                                        Tagged::from_simple_spanned_item(
+                                            Value::string(cmd),
+                                            Span::unknown(),
+                                        ),
+                                        &context.registry().clone(),
+                                    )?,
+                                ));
+                            }
+                            _ => {
+                                context.shell_manager.insert_at_current(Box::new(
+                                    HelpShell::index(&context.registry().clone())?,
+                                ));
+                            }
+                        }
+                    }
                     CommandAction::EnterValueShell(value) => {
                         context
                             .shell_manager

src/commands/clip.rs

@@ -18,6 +18,15 @@ pub mod clipboard {
         fn name(&self) -> &str {
             "clip"
         }
+
+        fn signature(&self) -> Signature {
+            Signature::build("clip")
+        }
+
+        fn usage(&self) -> &str {
+            "Copy the contents of the pipeline to the copy/paste buffer"
+        }
+
         fn run(
             &self,
             args: CommandArgs,
@@ -25,10 +34,6 @@ pub mod clipboard {
         ) -> Result<OutputStream, ShellError> {
             args.process(registry, clip)?.run()
         }
-
-        fn signature(&self) -> Signature {
-            Signature::build("clip")
-        }
     }
 
     pub fn clip(

src/commands/command.rs

@@ -417,6 +417,7 @@ pub enum CommandAction {
     Exit,
     EnterShell(String),
     EnterValueShell(Tagged<Value>),
+    EnterHelpShell(Tagged<Value>),
     PreviousShell,
     NextShell,
     LeaveShell,
@@ -434,6 +435,9 @@ impl ToDebug for CommandAction {
             CommandAction::EnterValueShell(t) => {
                 write!(f, "action:enter-value-shell={:?}", t.debug())
             }
+            CommandAction::EnterHelpShell(t) => {
+                write!(f, "action:enter-help-shell={:?}", t.debug())
+            }
             CommandAction::PreviousShell => write!(f, "action:previous-shell"),
             CommandAction::NextShell => write!(f, "action:next-shell"),
             CommandAction::LeaveShell => write!(f, "action:leave-shell"),
@@ -488,26 +492,42 @@ impl ReturnSuccess {
 pub trait WholeStreamCommand: Send + Sync {
     fn name(&self) -> &str;
 
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &registry::CommandRegistry,
-    ) -> Result<OutputStream, ShellError>;
-
     fn signature(&self) -> Signature {
         Signature {
             name: self.name().to_string(),
+            usage: self.usage().to_string(),
             positional: vec![],
             rest_positional: None,
             named: indexmap::IndexMap::new(),
             is_filter: true,
         }
     }
+
+    fn usage(&self) -> &str;
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &registry::CommandRegistry,
+    ) -> Result<OutputStream, ShellError>;
 }
 
 pub trait PerItemCommand: Send + Sync {
     fn name(&self) -> &str;
 
+    fn signature(&self) -> Signature {
+        Signature {
+            name: self.name().to_string(),
+            usage: self.usage().to_string(),
+            positional: vec![],
+            rest_positional: None,
+            named: indexmap::IndexMap::new(),
+            is_filter: true,
+        }
+    }
+
+    fn usage(&self) -> &str;
+
     fn run(
         &self,
         call_info: &CallInfo,
@@ -515,16 +535,6 @@ pub trait PerItemCommand: Send + Sync {
         raw_args: &RawCommandArgs,
         input: Tagged<Value>,
     ) -> Result<OutputStream, ShellError>;
-
-    fn signature(&self) -> Signature {
-        Signature {
-            name: self.name().to_string(),
-            positional: vec![],
-            rest_positional: None,
-            named: indexmap::IndexMap::new(),
-            is_filter: true,
-        }
-    }
 }
 
 pub enum Command {
@@ -547,6 +557,13 @@ impl Command {
         }
     }
 
+    pub fn usage(&self) -> &str {
+        match self {
+            Command::WholeStream(command) => command.usage(),
+            Command::PerItem(command) => command.usage(),
+        }
+    }
+
     pub fn run(&self, args: CommandArgs, registry: &registry::CommandRegistry) -> OutputStream {
         match self {
             Command::WholeStream(command) => match command.run(args, registry) {
@@ -618,6 +635,10 @@ impl WholeStreamCommand for FnFilterCommand {
         &self.name
     }
 
+    fn usage(&self) -> &str {
+        "usage"
+    }
+
     fn run(
         &self,
         args: CommandArgs,

src/commands/config.rs

@@ -32,6 +32,10 @@ impl WholeStreamCommand for Config {
             .switch("path")
     }
 
+    fn usage(&self) -> &str {
+        "Configuration management."
+    }
+
     fn run(
         &self,
         args: CommandArgs,

src/commands/cp.rs

@@ -15,16 +15,6 @@ pub struct CopyArgs {
 }
 
 impl PerItemCommand for Cpy {
-    fn run(
-        &self,
-        call_info: &CallInfo,
-        _registry: &CommandRegistry,
-        raw_args: &RawCommandArgs,
-        _input: Tagged<Value>,
-    ) -> Result<OutputStream, ShellError> {
-        call_info.process(&raw_args.shell_manager, cp)?.run()
-    }
-
     fn name(&self) -> &str {
         "cp"
     }
@@ -36,6 +26,20 @@ impl PerItemCommand for Cpy {
             .named("file", SyntaxType::Any)
             .switch("recursive")
     }
+
+    fn usage(&self) -> &str {
+        "Copy files."
+    }
+
+    fn run(
+        &self,
+        call_info: &CallInfo,
+        _registry: &CommandRegistry,
+        raw_args: &RawCommandArgs,
+        _input: Tagged<Value>,
+    ) -> Result<OutputStream, ShellError> {
+        call_info.process(&raw_args.shell_manager, cp)?.run()
+    }
 }
 
 fn cp(args: CopyArgs, context: &RunnablePerItemContext) -> Result<OutputStream, ShellError> {

src/commands/date.rs

@@ -12,6 +12,20 @@ use indexmap::IndexMap;
 pub struct Date;
 
 impl WholeStreamCommand for Date {
+    fn name(&self) -> &str {
+        "date"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("date")
+            .switch("utc")
+            .switch("local")
+    }
+
+    fn usage(&self) -> &str {
+        "Get the current datetime."
+    }
+
     fn run(
         &self,
         args: CommandArgs,
@@ -19,13 +33,6 @@ impl WholeStreamCommand for Date {
     ) -> Result<OutputStream, ShellError> {
         date(args, registry)
     }
-    fn name(&self) -> &str {
-        "date"
-    }
-
-    fn signature(&self) -> Signature {
-        Signature::build("date").switch("utc").switch("local")
-    }
 }
 
 pub fn date_to_value<T: TimeZone>(dt: DateTime<T>, span: Span) -> Tagged<Value>

src/commands/debug.rs

@@ -5,14 +5,6 @@ use crate::prelude::*;
 pub struct Debug;
 
 impl WholeStreamCommand for Debug {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        debug(args, registry)
-    }
-
     fn name(&self) -> &str {
         "debug"
     }
@@ -20,6 +12,18 @@ impl WholeStreamCommand for Debug {
     fn signature(&self) -> Signature {
         Signature::build("debug")
     }
+
+    fn usage(&self) -> &str {
+        "Debug input fed."
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        debug(args, registry)
+    }
 }
 
 pub fn debug(args: CommandArgs, _registry: &CommandRegistry) -> Result<OutputStream, ShellError> {

src/commands/enter.rs

@@ -17,6 +17,10 @@ impl PerItemCommand for Enter {
         Signature::build("enter").required("location", SyntaxType::Block)
     }
 
+    fn usage(&self) -> &str {
+        "Create a new shell and begin at this path."
+    }
+
     fn run(
         &self,
         call_info: &CallInfo,
@@ -33,7 +37,13 @@ impl PerItemCommand for Enter {
             } => {
                 let location = location.to_string();
                 let location_clone = location.to_string();
-                if PathBuf::from(location).is_dir() {
+
+                if registry.has(&location) {
+                    Ok(vec![Ok(ReturnSuccess::Action(CommandAction::EnterHelpShell(
+                        Value::string(location_clone).tagged(Tag::unknown()),
+                    )))]
+                    .into())
+                } else if PathBuf::from(location).is_dir() {
                     Ok(vec![Ok(ReturnSuccess::Action(CommandAction::EnterShell(
                         location_clone,
                     )))]

src/commands/exit.rs

@@ -6,6 +6,19 @@ use crate::prelude::*;
 pub struct Exit;
 
 impl WholeStreamCommand for Exit {
+    fn name(&self) -> &str {
+        "exit"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("exit")
+            .switch("now")
+    }
+
+    fn usage(&self) -> &str {
+        "Exit the current shell (or all shells)"
+    }
+
     fn run(
         &self,
         args: CommandArgs,
@@ -13,14 +26,6 @@ impl WholeStreamCommand for Exit {
     ) -> Result<OutputStream, ShellError> {
         exit(args, registry)
     }
-
-    fn name(&self) -> &str {
-        "exit"
-    }
-
-    fn signature(&self) -> Signature {
-        Signature::build("exit").switch("now")
-    }
 }
 
 pub fn exit(args: CommandArgs, registry: &CommandRegistry) -> Result<OutputStream, ShellError> {

src/commands/first.rs

@@ -6,6 +6,19 @@ use crate::prelude::*;
 pub struct First;
 
 impl WholeStreamCommand for First {
+    fn name(&self) -> &str {
+        "first"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("first")
+            .required("amount", SyntaxType::Literal)
+    }
+
+    fn usage(&self) -> &str {
+        "Show only the first number of rows."
+    }
+
     fn run(
         &self,
         args: CommandArgs,
@@ -13,14 +26,6 @@ impl WholeStreamCommand for First {
     ) -> Result<OutputStream, ShellError> {
         first(args, registry)
     }
-
-    fn name(&self) -> &str {
-        "first"
-    }
-
-    fn signature(&self) -> Signature {
-        Signature::build("first").required("amount", SyntaxType::Literal)
-    }
 }
 
 fn first(args: CommandArgs, registry: &CommandRegistry) -> Result<OutputStream, ShellError> {

src/commands/from_array.rs

@@ -5,14 +5,6 @@ use crate::prelude::*;
 pub struct FromArray;
 
 impl WholeStreamCommand for FromArray {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        from_array(args, registry)
-    }
-
     fn name(&self) -> &str {
         "from-array"
     }
@@ -20,6 +12,18 @@ impl WholeStreamCommand for FromArray {
     fn signature(&self) -> Signature {
         Signature::build("from-array")
     }
+
+    fn usage(&self) -> &str {
+        "Expand an array/list into rows"
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        from_array(args, registry)
+    }
 }
 
 fn from_array(args: CommandArgs, _registry: &CommandRegistry) -> Result<OutputStream, ShellError> {

src/commands/from_bson.rs

@@ -7,14 +7,6 @@ use std::str::FromStr;
 pub struct FromBSON;
 
 impl WholeStreamCommand for FromBSON {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        from_bson(args, registry)
-    }
-
     fn name(&self) -> &str {
         "from-bson"
     }
@@ -22,6 +14,18 @@ impl WholeStreamCommand for FromBSON {
     fn signature(&self) -> Signature {
         Signature::build("from-bson")
     }
+
+    fn usage(&self) -> &str {
+        "Parse text as .bson and create table."
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        from_bson(args, registry)
+    }
 }
 
 fn convert_bson_value_to_nu_value(v: &Bson, tag: impl Into<Tag>) -> Tagged<Value> {

src/commands/from_csv.rs

@@ -16,7 +16,12 @@ impl WholeStreamCommand for FromCSV {
     }
 
     fn signature(&self) -> Signature {
-        Signature::build("from-csv").switch("headerless")
+        Signature::build("from-csv")
+            .switch("headerless")
+    }
+
+    fn usage(&self) -> &str {
+        "Parse text as .csv and create table"
     }
 
     fn run(

src/commands/from_ini.rs

@@ -6,14 +6,6 @@ use std::collections::HashMap;
 pub struct FromINI;
 
 impl WholeStreamCommand for FromINI {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        from_ini(args, registry)
-    }
-
     fn name(&self) -> &str {
         "from-ini"
     }
@@ -21,6 +13,18 @@ impl WholeStreamCommand for FromINI {
     fn signature(&self) -> Signature {
         Signature::build("from-ini")
     }
+
+    fn usage(&self) -> &str {
+        "Parse text as .ini and create table"
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        from_ini(args, registry)
+    }
 }
 
 fn convert_ini_second_to_nu_value(

src/commands/from_json.rs

@@ -15,7 +15,12 @@ impl WholeStreamCommand for FromJSON {
     }
 
     fn signature(&self) -> Signature {
-        Signature::build("from-json").switch("objects")
+        Signature::build("from-json")
+            .switch("objects")
+    }
+
+    fn usage(&self) -> &str {
+        "Parse text as .json and create table."
     }
 
     fn run(

src/commands/from_sqlite.rs

@@ -9,14 +9,6 @@ use std::path::Path;
 pub struct FromSQLite;
 
 impl WholeStreamCommand for FromSQLite {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        from_sqlite(args, registry)
-    }
-
     fn name(&self) -> &str {
         "from-sqlite"
     }
@@ -24,11 +16,11 @@ impl WholeStreamCommand for FromSQLite {
     fn signature(&self) -> Signature {
         Signature::build("from-sqlite")
     }
-}
 
-pub struct FromDB;
+    fn usage(&self) -> &str {
+        "Parse binary data as sqlite .db and create table."
+    }
 
-impl WholeStreamCommand for FromDB {
     fn run(
         &self,
         args: CommandArgs,
@@ -36,7 +28,11 @@ impl WholeStreamCommand for FromDB {
     ) -> Result<OutputStream, ShellError> {
         from_sqlite(args, registry)
     }
+}
 
+pub struct FromDB;
+
+impl WholeStreamCommand for FromDB {
     fn name(&self) -> &str {
         "from-db"
     }
@@ -44,6 +40,18 @@ impl WholeStreamCommand for FromDB {
     fn signature(&self) -> Signature {
         Signature::build("from-db")
     }
+
+    fn usage(&self) -> &str {
+        "Parse binary data as db and create table."
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        from_sqlite(args, registry)
+    }
 }
 
 pub fn convert_sqlite_file_to_nu_value(

src/commands/from_toml.rs

@@ -5,14 +5,6 @@ use crate::prelude::*;
 pub struct FromTOML;
 
 impl WholeStreamCommand for FromTOML {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        from_toml(args, registry)
-    }
-
     fn name(&self) -> &str {
         "from-toml"
     }
@@ -20,6 +12,18 @@ impl WholeStreamCommand for FromTOML {
     fn signature(&self) -> Signature {
         Signature::build("from-toml")
     }
+
+    fn usage(&self) -> &str {
+        "Parse text as .toml and create table."
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        from_toml(args, registry)
+    }
 }
 
 pub fn convert_toml_value_to_nu_value(v: &toml::Value, tag: impl Into<Tag>) -> Tagged<Value> {

src/commands/from_tsv.rs

@@ -19,6 +19,10 @@ impl WholeStreamCommand for FromTSV {
         Signature::build("from-tsv").switch("headerless")
     }
 
+    fn usage(&self) -> &str {
+        "Parse text as .tsv and create table."
+    }
+
     fn run(
         &self,
         args: CommandArgs,

src/commands/from_xml.rs

@@ -5,14 +5,6 @@ use crate::prelude::*;
 pub struct FromXML;
 
 impl WholeStreamCommand for FromXML {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        from_xml(args, registry)
-    }
-
     fn name(&self) -> &str {
         "from-xml"
     }
@@ -20,6 +12,18 @@ impl WholeStreamCommand for FromXML {
     fn signature(&self) -> Signature {
         Signature::build("from-xml")
     }
+
+    fn usage(&self) -> &str {
+        "Parse text as .xml and create table."
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        from_xml(args, registry)
+    }
 }
 
 fn from_node_to_value<'a, 'd>(n: &roxmltree::Node<'a, 'd>, tag: impl Into<Tag>) -> Tagged<Value> {

src/commands/from_yaml.rs

@@ -5,14 +5,6 @@ use crate::prelude::*;
 pub struct FromYAML;
 
 impl WholeStreamCommand for FromYAML {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        from_yaml(args, registry)
-    }
-
     fn name(&self) -> &str {
         "from-yaml"
     }
@@ -20,11 +12,11 @@ impl WholeStreamCommand for FromYAML {
     fn signature(&self) -> Signature {
         Signature::build("from-yaml")
     }
-}
 
-pub struct FromYML;
+    fn usage(&self) -> &str {
+        "Parse text as .yaml/.yml and create table."
+    }
 
-impl WholeStreamCommand for FromYML {
     fn run(
         &self,
         args: CommandArgs,
@@ -32,7 +24,11 @@ impl WholeStreamCommand for FromYML {
     ) -> Result<OutputStream, ShellError> {
         from_yaml(args, registry)
     }
+}
 
+pub struct FromYML;
+
+impl WholeStreamCommand for FromYML {
     fn name(&self) -> &str {
         "from-yml"
     }
@@ -40,6 +36,18 @@ impl WholeStreamCommand for FromYML {
     fn signature(&self) -> Signature {
         Signature::build("from-yml")
     }
+
+    fn usage(&self) -> &str {
+        "Parse text as .yaml/.yml and create table."
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        from_yaml(args, registry)
+    }
 }
 
 fn convert_yaml_value_to_nu_value(v: &serde_yaml::Value, tag: impl Into<Tag>) -> Tagged<Value> {

src/commands/get.rs

@@ -15,6 +15,14 @@ impl WholeStreamCommand for Get {
         "get"
     }
 
+    fn signature(&self) -> Signature {
+        Signature::build("get").rest(SyntaxType::Member)
+    }
+
+    fn usage(&self) -> &str {
+        "Open given cells as text."
+    }
+
     fn run(
         &self,
         args: CommandArgs,
@@ -22,10 +30,6 @@ impl WholeStreamCommand for Get {
     ) -> Result<OutputStream, ShellError> {
         args.process(registry, get)?.run()
     }
-
-    fn signature(&self) -> Signature {
-        Signature::build("get").rest(SyntaxType::Member)
-    }
 }
 
 fn get_member(path: &Tagged<String>, obj: &Tagged<Value>) -> Result<Tagged<Value>, ShellError> {

src/commands/help.rs

@@ -0,0 +1,55 @@
+use crate::commands::command::CommandAction;
+use crate::commands::PerItemCommand;
+use crate::errors::ShellError;
+use crate::parser::registry;
+use crate::prelude::*;
+
+pub struct Help;
+
+impl PerItemCommand for Help {
+    fn name(&self) -> &str {
+        "help"
+    }
+
+    fn signature(&self) -> registry::Signature {
+        Signature::build("help").rest(SyntaxType::Any)
+    }
+
+    fn usage(&self) -> &str {
+        "Display help information about commands."
+    }
+
+    fn run(
+        &self,
+        call_info: &CallInfo,
+        _registry: &CommandRegistry,
+        _raw_args: &RawCommandArgs,
+        _input: Tagged<Value>,
+    ) -> Result<OutputStream, ShellError> {
+        let span = call_info.name_span;
+
+        if call_info.args.len() == 0 {
+            return Ok(
+                vec![
+                Ok(ReturnSuccess::Action(
+                    CommandAction::EnterHelpShell(
+                        Tagged::from_simple_spanned_item(Value::nothing(), span)
+                    )))].into()
+            )
+        }
+
+        match call_info.args.expect_nth(0)? {
+            Tagged {
+                item: Value::Primitive(Primitive::String(document)),
+                ..
+            } => Ok(vec![Ok(ReturnSuccess::Action(CommandAction::EnterHelpShell(
+                Tagged::from_simple_spanned_item(Value::string(document), span)
+            )))]
+            .into()),
+            x => Ok(
+                vec![Ok(ReturnSuccess::Action(CommandAction::EnterHelpShell(x.clone())))]
+                .into(),
+            ),
+        }
+    }
+}

src/commands/last.rs

@@ -6,6 +6,19 @@ use crate::prelude::*;
 pub struct Last;
 
 impl WholeStreamCommand for Last {
+    fn name(&self) -> &str {
+        "last"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("last")
+            .required("amount", SyntaxType::Number)
+    }
+
+    fn usage(&self) -> &str {
+        "Show only the last number of rows."
+    }
+
     fn run(
         &self,
         args: CommandArgs,
@@ -13,14 +26,6 @@ impl WholeStreamCommand for Last {
     ) -> Result<OutputStream, ShellError> {
         last(args, registry)
     }
-
-    fn name(&self) -> &str {
-        "last"
-    }
-
-    fn signature(&self) -> Signature {
-        Signature::build("last").required("amount", SyntaxType::Literal)
-    }
 }
 
 fn last(args: CommandArgs, registry: &CommandRegistry) -> Result<OutputStream, ShellError> {

src/commands/lines.rs

@@ -7,14 +7,6 @@ use log::trace;
 pub struct Lines;
 
 impl WholeStreamCommand for Lines {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        lines(args, registry)
-    }
-
     fn name(&self) -> &str {
         "lines"
     }
@@ -22,6 +14,18 @@ impl WholeStreamCommand for Lines {
     fn signature(&self) -> Signature {
         Signature::build("lines")
     }
+
+    fn usage(&self) -> &str {
+        "Split single string into rows, one per line."
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        lines(args, registry)
+    }
 }
 
 // TODO: "Amount remaining" wrapper

src/commands/ls.rs

@@ -5,14 +5,6 @@ use crate::prelude::*;
 pub struct LS;
 
 impl WholeStreamCommand for LS {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        ls(args, registry)
-    }
-
     fn name(&self) -> &str {
         "ls"
     }
@@ -20,6 +12,18 @@ impl WholeStreamCommand for LS {
     fn signature(&self) -> Signature {
         Signature::build("ls").optional("path", SyntaxType::Path)
     }
+
+    fn usage(&self) -> &str {
+        "View the contents of the current or given path."
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        ls(args, registry)
+    }
 }
 
 fn ls(args: CommandArgs, registry: &CommandRegistry) -> Result<OutputStream, ShellError> {

src/commands/mkdir.rs

@@ -12,6 +12,18 @@ pub struct MkdirArgs {
 }
 
 impl PerItemCommand for Mkdir {
+    fn name(&self) -> &str {
+        "mkdir"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("mkdir").rest(SyntaxType::Path)
+    }
+
+    fn usage(&self) -> &str {
+        "Make directories, creates intermediary directories as required."
+    }
+
     fn run(
         &self,
         call_info: &CallInfo,
@@ -21,14 +33,6 @@ impl PerItemCommand for Mkdir {
     ) -> Result<OutputStream, ShellError> {
         call_info.process(&raw_args.shell_manager, mkdir)?.run()
     }
-
-    fn name(&self) -> &str {
-        "mkdir"
-    }
-
-    fn signature(&self) -> Signature {
-        Signature::build("mkdir").rest(SyntaxType::Path)
-    }
 }
 
 fn mkdir(args: MkdirArgs, context: &RunnablePerItemContext) -> Result<OutputStream, ShellError> {

src/commands/mv.rs

@@ -25,6 +25,10 @@ impl PerItemCommand for Move {
             .named("file", SyntaxType::Any)
     }
 
+    fn usage(&self) -> &str {
+        "Move files or directories."
+    }
+
     fn run(
         &self,
         call_info: &CallInfo,

src/commands/next.rs

@@ -6,14 +6,6 @@ use crate::prelude::*;
 pub struct Next;
 
 impl WholeStreamCommand for Next {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        next(args, registry)
-    }
-
     fn name(&self) -> &str {
         "n"
     }
@@ -21,6 +13,18 @@ impl WholeStreamCommand for Next {
     fn signature(&self) -> Signature {
         Signature::build("n")
     }
+
+    fn usage(&self) -> &str {
+        "Go to next shell."
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        next(args, registry)
+    }
 }
 
 fn next(_args: CommandArgs, _registry: &CommandRegistry) -> Result<OutputStream, ShellError> {

src/commands/nth.rs

@@ -11,14 +11,6 @@ struct NthArgs {
 pub struct Nth;
 
 impl WholeStreamCommand for Nth {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        args.process(registry, nth)?.run()
-    }
-
     fn name(&self) -> &str {
         "nth"
     }
@@ -26,6 +18,18 @@ impl WholeStreamCommand for Nth {
     fn signature(&self) -> Signature {
         Signature::build("nth").required("amount", SyntaxType::Any)
     }
+
+    fn usage(&self) -> &str {
+        "Return only the selected row"
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        args.process(registry, nth)?.run()
+    }
 }
 
 fn nth(

src/commands/open.rs

@@ -23,6 +23,10 @@ impl PerItemCommand for Open {
             .switch("raw")
     }
 
+    fn usage(&self) -> &str {
+        "Load a file into a cell, convert to table if possible (avoid by appending '--raw')"
+    }
+
     fn run(
         &self,
         call_info: &CallInfo,

src/commands/pick.rs

@@ -20,6 +20,10 @@ impl WholeStreamCommand for Pick {
         Signature::build("pick").rest(SyntaxType::Any)
     }
 
+    fn usage(&self) -> &str {
+        "Down-select table to only these columns."
+    }
+
     fn run(
         &self,
         args: CommandArgs,

src/commands/plugin.rs

@@ -51,6 +51,10 @@ impl WholeStreamCommand for PluginCommand {
         self.config.clone()
     }
 
+    fn usage(&self) -> &str {
+        &self.config.usage
+    }
+
     fn run(
         &self,
         args: CommandArgs,
@@ -270,6 +274,10 @@ impl WholeStreamCommand for PluginSink {
         self.config.clone()
     }
 
+    fn usage(&self) -> &str {
+        &self.config.usage
+    }
+
     fn run(
         &self,
         args: CommandArgs,

src/commands/post.rs

@@ -27,6 +27,10 @@ impl PerItemCommand for Post {
             .switch("raw")
     }
 
+    fn usage(&self) -> &str {
+        "Post content to a url and retrieve data as a table if possible."
+    }
+
     fn run(
         &self,
         call_info: &CallInfo,

src/commands/prev.rs

@@ -7,14 +7,6 @@ use crate::commands::WholeStreamCommand;
 pub struct Previous;
 
 impl WholeStreamCommand for Previous {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        previous(args, registry)
-    }
-
     fn name(&self) -> &str {
         "p"
     }
@@ -22,6 +14,18 @@ impl WholeStreamCommand for Previous {
     fn signature(&self) -> Signature {
         Signature::build("p")
     }
+
+    fn usage(&self) -> &str {
+        "Go to previous shell."
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        previous(args, registry)
+    }
 }
 
 fn previous(_args: CommandArgs, _registry: &CommandRegistry) -> Result<OutputStream, ShellError> {

src/commands/ps.rs

@@ -12,14 +12,6 @@ use heim::units::{ratio, Ratio};
 pub struct PS;
 
 impl WholeStreamCommand for PS {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        ps(args, registry)
-    }
-
     fn name(&self) -> &str {
         "ps"
     }
@@ -27,6 +19,18 @@ impl WholeStreamCommand for PS {
     fn signature(&self) -> Signature {
         Signature::build("ps")
     }
+
+    fn usage(&self) -> &str {
+        "View current processes."
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        ps(args, registry)
+    }
 }
 
 async fn usage(process: Process) -> ProcessResult<(process::Process, Ratio)> {

src/commands/reject.rs

@@ -11,14 +11,6 @@ pub struct RejectArgs {
 pub struct Reject;
 
 impl WholeStreamCommand for Reject {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        args.process(registry, reject)?.run()
-    }
-
     fn name(&self) -> &str {
         "reject"
     }
@@ -26,6 +18,18 @@ impl WholeStreamCommand for Reject {
     fn signature(&self) -> Signature {
         Signature::build("reject").rest(SyntaxType::Member)
     }
+
+    fn usage(&self) -> &str {
+        "Remove the given columns from the table."
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        args.process(registry, reject)?.run()
+    }
 }
 
 fn reject(

src/commands/reverse.rs

@@ -6,14 +6,6 @@ use crate::prelude::*;
 pub struct Reverse;
 
 impl WholeStreamCommand for Reverse {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        reverse(args, registry)
-    }
-
     fn name(&self) -> &str {
         "reverse"
     }
@@ -21,6 +13,18 @@ impl WholeStreamCommand for Reverse {
     fn signature(&self) -> Signature {
         Signature::build("reverse")
     }
+
+    fn usage(&self) -> &str {
+        "Reverses the table."
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        reverse(args, registry)
+    }
 }
 
 fn reverse(args: CommandArgs, registry: &CommandRegistry) -> Result<OutputStream, ShellError> {

src/commands/rm.rs

@@ -24,6 +24,10 @@ impl PerItemCommand for Remove {
             .switch("recursive")
     }
 
+    fn usage(&self) -> &str {
+        "Remove a file, (for removing directory append '--recursive')"
+    }
+
     fn run(
         &self,
         call_info: &CallInfo,

src/commands/save.rs

@@ -23,6 +23,10 @@ impl WholeStreamCommand for Save {
             .switch("raw")
     }
 
+    fn usage(&self) -> &str {
+        "Save the contents of the pipeline to a file."
+    }
+
     fn run(
         &self,
         args: CommandArgs,

src/commands/shells.rs

@@ -6,14 +6,6 @@ use crate::prelude::*;
 pub struct Shells;
 
 impl WholeStreamCommand for Shells {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        shells(args, registry)
-    }
-
     fn name(&self) -> &str {
         "shells"
     }
@@ -21,6 +13,18 @@ impl WholeStreamCommand for Shells {
     fn signature(&self) -> Signature {
         Signature::build("shells")
     }
+
+    fn usage(&self) -> &str {
+        "Display the list of current shells."
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        shells(args, registry)
+    }
 }
 
 fn shells(args: CommandArgs, _registry: &CommandRegistry) -> Result<OutputStream, ShellError> {

src/commands/size.rs

@@ -6,14 +6,6 @@ use crate::prelude::*;
 pub struct Size;
 
 impl WholeStreamCommand for Size {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        size(args, registry)
-    }
-
     fn name(&self) -> &str {
         "size"
     }
@@ -21,6 +13,18 @@ impl WholeStreamCommand for Size {
     fn signature(&self) -> Signature {
         Signature::build("size")
     }
+
+    fn usage(&self) -> &str {
+        "Gather word count statistics on the text."
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        size(args, registry)
+    }
 }
 
 fn size(args: CommandArgs, _registry: &CommandRegistry) -> Result<OutputStream, ShellError> {

src/commands/skip_while.rs

@@ -20,6 +20,10 @@ impl WholeStreamCommand for SkipWhile {
             .filter()
     }
 
+    fn usage(&self) -> &str {
+        "Skips rows while the condition matches."
+    }
+
     fn run(
         &self,
         args: CommandArgs,

src/commands/sort_by.rs

@@ -10,14 +10,6 @@ pub struct SortByArgs {
 }
 
 impl WholeStreamCommand for SortBy {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        args.process(registry, sort_by)?.run()
-    }
-
     fn name(&self) -> &str {
         "sort-by"
     }
@@ -25,6 +17,18 @@ impl WholeStreamCommand for SortBy {
     fn signature(&self) -> Signature {
         Signature::build("sort-by").rest(SyntaxType::String)
     }
+
+    fn usage(&self) -> &str {
+        "Sort by the given columns."
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        args.process(registry, sort_by)?.run()
+    }
 }
 
 fn sort_by(

src/commands/split_column.rs

@@ -15,14 +15,6 @@ struct SplitColumnArgs {
 pub struct SplitColumn;
 
 impl WholeStreamCommand for SplitColumn {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        args.process(registry, split_column)?.run()
-    }
-
     fn name(&self) -> &str {
         "split-column"
     }
@@ -33,6 +25,18 @@ impl WholeStreamCommand for SplitColumn {
             .switch("collapse-empty")
             .rest(SyntaxType::Member)
     }
+
+    fn usage(&self) -> &str {
+        "Split row contents across multiple columns via the separator."
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        args.process(registry, split_column)?.run()
+    }
 }
 
 fn split_column(

src/commands/split_row.rs

@@ -12,6 +12,19 @@ struct SplitRowArgs {
 pub struct SplitRow;
 
 impl WholeStreamCommand for SplitRow {
+    fn name(&self) -> &str {
+        "split-row"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("split-row")
+            .required("separator", SyntaxType::Any)
+    }
+
+    fn usage(&self) -> &str {
+        "Split row contents over multiple rows via the separator."
+    }
+
     fn run(
         &self,
         args: CommandArgs,
@@ -19,14 +32,6 @@ impl WholeStreamCommand for SplitRow {
     ) -> Result<OutputStream, ShellError> {
         args.process(registry, split_row)?.run()
     }
-
-    fn name(&self) -> &str {
-        "split-row"
-    }
-
-    fn signature(&self) -> Signature {
-        Signature::build("split-row").required("separator", SyntaxType::Any)
-    }
 }
 
 fn split_row(

src/commands/table.rs

@@ -13,6 +13,15 @@ impl WholeStreamCommand for Table {
     fn name(&self) -> &str {
         "table"
     }
+
+    fn signature(&self) -> Signature {
+        Signature::build("table")
+    }
+
+    fn usage(&self) -> &str {
+        "View the contents of the pipeline as a table."
+    }
+
     fn run(
         &self,
         args: CommandArgs,
@@ -20,9 +29,6 @@ impl WholeStreamCommand for Table {
     ) -> Result<OutputStream, ShellError> {
         args.process(registry, table)?.run()
     }
-    fn signature(&self) -> Signature {
-        Signature::build("table")
-    }
 }
 
 pub fn table(_args: TableArgs, context: RunnableContext) -> Result<OutputStream, ShellError> {

src/commands/tags.rs

@@ -6,14 +6,6 @@ use crate::prelude::*;
 pub struct Tags;
 
 impl WholeStreamCommand for Tags {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        tags(args, registry)
-    }
-
     fn name(&self) -> &str {
         "tags"
     }
@@ -21,6 +13,18 @@ impl WholeStreamCommand for Tags {
     fn signature(&self) -> Signature {
         Signature::build("tags")
     }
+
+    fn usage(&self) -> &str {
+        "Read the tags (metadata) for values."
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        tags(args, registry)
+    }
 }
 
 fn tags(args: CommandArgs, _registry: &CommandRegistry) -> Result<OutputStream, ShellError> {

src/commands/to_array.rs

@@ -5,14 +5,6 @@ use crate::prelude::*;
 pub struct ToArray;
 
 impl WholeStreamCommand for ToArray {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        to_array(args, registry)
-    }
-
     fn name(&self) -> &str {
         "to-array"
     }
@@ -20,6 +12,18 @@ impl WholeStreamCommand for ToArray {
     fn signature(&self) -> Signature {
         Signature::build("to-array")
     }
+
+    fn usage(&self) -> &str {
+        "Collapse rows into a single list."
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        to_array(args, registry)
+    }
 }
 
 fn to_array(args: CommandArgs, registry: &CommandRegistry) -> Result<OutputStream, ShellError> {

src/commands/to_bson.rs

@@ -7,14 +7,6 @@ use std::convert::TryInto;
 pub struct ToBSON;
 
 impl WholeStreamCommand for ToBSON {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        to_bson(args, registry)
-    }
-
     fn name(&self) -> &str {
         "to-bson"
     }
@@ -22,6 +14,18 @@ impl WholeStreamCommand for ToBSON {
     fn signature(&self) -> Signature {
         Signature::build("to-bson")
     }
+
+    fn usage(&self) -> &str {
+        "Convert table into .bson text."
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        to_bson(args, registry)
+    }
 }
 
 pub fn value_to_bson_value(v: &Value) -> Bson {

src/commands/to_csv.rs

@@ -16,7 +16,12 @@ impl WholeStreamCommand for ToCSV {
     }
 
     fn signature(&self) -> Signature {
-        Signature::build("to-csv").switch("headerless")
+        Signature::build("to-csv")
+            .switch("headerless")
+    }
+
+    fn usage(&self) -> &str {
+        "Convert table into .csv text "
     }
 
     fn run(

src/commands/to_json.rs

@@ -5,14 +5,6 @@ use crate::prelude::*;
 pub struct ToJSON;
 
 impl WholeStreamCommand for ToJSON {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        to_json(args, registry)
-    }
-
     fn name(&self) -> &str {
         "to-json"
     }
@@ -20,6 +12,18 @@ impl WholeStreamCommand for ToJSON {
     fn signature(&self) -> Signature {
         Signature::build("to-json")
     }
+
+    fn usage(&self) -> &str {
+        "Convert table into .json text"
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        to_json(args, registry)
+    }
 }
 
 pub fn value_to_json_value(v: &Value) -> serde_json::Value {

src/commands/to_sqlite.rs

@@ -8,14 +8,6 @@ use std::io::Read;
 pub struct ToSQLite;
 
 impl WholeStreamCommand for ToSQLite {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        to_sqlite(args, registry)
-    }
-
     fn name(&self) -> &str {
         "to-sqlite"
     }
@@ -23,11 +15,11 @@ impl WholeStreamCommand for ToSQLite {
     fn signature(&self) -> Signature {
         Signature::build("to-sqlite")
     }
-}
 
-pub struct ToDB;
+    fn usage(&self) -> &str {
+        "Convert table to sqlite .db binary data"
+    }
 
-impl WholeStreamCommand for ToDB {
     fn run(
         &self,
         args: CommandArgs,
@@ -35,7 +27,11 @@ impl WholeStreamCommand for ToDB {
     ) -> Result<OutputStream, ShellError> {
         to_sqlite(args, registry)
     }
+}
 
+pub struct ToDB;
+
+impl WholeStreamCommand for ToDB {
     fn name(&self) -> &str {
         "to-db"
     }
@@ -43,6 +39,18 @@ impl WholeStreamCommand for ToDB {
     fn signature(&self) -> Signature {
         Signature::build("to-db")
     }
+
+    fn usage(&self) -> &str {
+        "Convert table to db data"
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        to_sqlite(args, registry)
+    }
 }
 
 fn comma_concat(acc: String, current: String) -> String {

src/commands/to_toml.rs

@@ -6,14 +6,6 @@ use crate::prelude::*;
 pub struct ToTOML;
 
 impl WholeStreamCommand for ToTOML {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        to_toml(args, registry)
-    }
-
     fn name(&self) -> &str {
         "to-toml"
     }
@@ -21,6 +13,18 @@ impl WholeStreamCommand for ToTOML {
     fn signature(&self) -> Signature {
         Signature::build("to-toml")
     }
+
+    fn usage(&self) -> &str {
+        "Convert table into .toml text"
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        to_toml(args, registry)
+    }
 }
 
 pub fn value_to_toml_value(v: &Value) -> Result<toml::Value, ShellError> {

src/commands/to_tsv.rs

@@ -16,7 +16,12 @@ impl WholeStreamCommand for ToTSV {
     }
 
     fn signature(&self) -> Signature {
-        Signature::build("to-tsv").switch("headerless")
+        Signature::build("to-tsv")
+            .switch("headerless")
+    }
+
+    fn usage(&self) -> &str {
+        "Convert table into .tsv text"
     }
 
     fn run(

src/commands/to_yaml.rs

@@ -5,14 +5,6 @@ use crate::prelude::*;
 pub struct ToYAML;
 
 impl WholeStreamCommand for ToYAML {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        to_yaml(args, registry)
-    }
-
     fn name(&self) -> &str {
         "to-yaml"
     }
@@ -20,6 +12,18 @@ impl WholeStreamCommand for ToYAML {
     fn signature(&self) -> Signature {
         Signature::build("to-yaml")
     }
+
+    fn usage(&self) -> &str {
+        "Convert table into .yaml/.yml text"
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        to_yaml(args, registry)
+    }
 }
 
 pub fn value_to_yaml_value(v: &Value) -> serde_yaml::Value {

src/commands/trim.rs

@@ -6,14 +6,6 @@ use crate::prelude::*;
 pub struct Trim;
 
 impl WholeStreamCommand for Trim {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        trim(args, registry)
-    }
-
     fn name(&self) -> &str {
         "trim"
     }
@@ -21,6 +13,18 @@ impl WholeStreamCommand for Trim {
     fn signature(&self) -> Signature {
         Signature::build("trim")
     }
+
+    fn usage(&self) -> &str {
+        "Trim leading and following whitespace from text data."
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        trim(args, registry)
+    }
 }
 
 fn trim(args: CommandArgs, _registry: &CommandRegistry) -> Result<OutputStream, ShellError> {

src/commands/version.rs

@@ -8,14 +8,6 @@ use indexmap::IndexMap;
 pub struct Version;
 
 impl WholeStreamCommand for Version {
-    fn run(
-        &self,
-        args: CommandArgs,
-        registry: &CommandRegistry,
-    ) -> Result<OutputStream, ShellError> {
-        date(args, registry)
-    }
-
     fn name(&self) -> &str {
         "version"
     }
@@ -23,6 +15,18 @@ impl WholeStreamCommand for Version {
     fn signature(&self) -> Signature {
         Signature::build("version")
     }
+
+    fn usage(&self) -> &str {
+        "Display Nu version"
+    }
+
+    fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        date(args, registry)
+    }
 }
 
 pub fn date(args: CommandArgs, registry: &CommandRegistry) -> Result<OutputStream, ShellError> {

src/commands/vtable.rs

@@ -12,6 +12,15 @@ impl WholeStreamCommand for VTable {
     fn name(&self) -> &str {
         "vtable"
     }
+
+    fn signature(&self) -> Signature {
+        Signature::build("vtable")
+    }
+
+    fn usage(&self) -> &str {
+        "View the contents of the pipeline as a vertical (rotated) table."
+    }
+
     fn run(
         &self,
         args: CommandArgs,
@@ -19,9 +28,6 @@ impl WholeStreamCommand for VTable {
     ) -> Result<OutputStream, ShellError> {
         args.process(registry, vtable)?.run()
     }
-    fn signature(&self) -> Signature {
-        Signature::build("vtable")
-    }
 }
 
 pub fn vtable(_args: VTableArgs, context: RunnableContext) -> Result<OutputStream, ShellError> {

src/commands/where_.rs

@@ -12,7 +12,12 @@ impl PerItemCommand for Where {
     }
 
     fn signature(&self) -> registry::Signature {
-        Signature::build("where").required("condition", SyntaxType::Block)
+        Signature::build("where")
+            .required("condition", SyntaxType::Block)
+    }
+
+    fn usage(&self) -> &str {
+        "Filter table to match the condition."
     }
 
     fn run(

src/commands/which_.rs

@@ -8,6 +8,19 @@ use crate::parser::registry::Signature;
 pub struct Which;
 
 impl WholeStreamCommand for Which {
+    fn name(&self) -> &str {
+        "which"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("which")
+            .required("name", SyntaxType::Any)
+    }
+
+    fn usage(&self) -> &str {
+        "Finds a program file."
+    }
+
     fn run(
         &self,
         args: CommandArgs,
@@ -15,13 +28,6 @@ impl WholeStreamCommand for Which {
     ) -> Result<OutputStream, ShellError> {
         which(args, registry)
     }
-    fn name(&self) -> &str {
-        "which"
-    }
-
-    fn signature(&self) -> Signature {
-        Signature::build("which").required("name", SyntaxType::Any)
-    }
 }
 
 pub fn which(args: CommandArgs, registry: &CommandRegistry) -> Result<OutputStream, ShellError> {

src/context.rs

@@ -53,7 +53,7 @@ impl CommandRegistry {
         registry.get(name).map(|c| c.clone())
     }
 
-    fn has(&self, name: &str) -> bool {
+    pub(crate) fn has(&self, name: &str) -> bool {
         let registry = self.registry.lock().unwrap();
 
         registry.contains_key(name)

src/object.rs

@@ -1,4 +1,5 @@
 pub(crate) mod base;
+pub(crate) mod command;
 pub(crate) mod config;
 pub(crate) mod dict;
 pub(crate) mod files;
@@ -8,5 +9,6 @@ pub(crate) mod types;
 
 #[allow(unused)]
 pub(crate) use base::{Block, Primitive, Switch, Value};
-pub(crate) use dict::{Dictionary, TaggedDictBuilder};
+pub(crate) use dict::{Dictionary, TaggedListBuilder, TaggedDictBuilder};
 pub(crate) use files::dir_entry_dict;
+pub(crate) use command::command_dict;

src/object/command.rs

@@ -0,0 +1,67 @@
+use crate::commands::command::Command;
+use crate::object::{TaggedDictBuilder, TaggedListBuilder, Value};
+use crate::parser::registry::{NamedType, PositionalType, Signature};
+use crate::prelude::*;
+use std::ops::Deref;
+
+pub(crate) fn command_dict(command: Arc<Command>, tag: impl Into<Tag>) -> Tagged<Value> {
+    let tag = tag.into();
+
+    let mut cmd_dict = TaggedDictBuilder::new(tag);
+
+    cmd_dict.insert("name", Value::string(command.name()));
+
+    cmd_dict.insert(
+        "type",
+        Value::string(match command.deref() {
+            Command::WholeStream(_) => "Command",
+            Command::PerItem(_) => "Filter",
+        }),
+    );
+
+    cmd_dict.insert_tagged("signature", signature_dict(command.signature(), tag));
+    cmd_dict.insert("usage", Value::string(command.usage()));
+
+    cmd_dict.into_tagged_value()
+}
+
+fn for_spec(name: &str, ty: &str, required: bool, tag: impl Into<Tag>) -> Tagged<Value> {
+    let tag = tag.into();
+
+    let mut spec = TaggedDictBuilder::new(tag);
+
+    spec.insert("name", Value::string(name));
+    spec.insert("type", Value::string(ty));
+    spec.insert("required", Value::string(if required { "yes" } else { "no" }));
+
+    spec.into_tagged_value()
+}
+
+fn signature_dict(signature: Signature, tag: impl Into<Tag>) -> Tagged<Value> {
+    let tag = tag.into();
+    let mut sig = TaggedListBuilder::new(tag);
+
+    for arg in signature.positional.iter() {
+        let is_required = match arg {
+            PositionalType::Mandatory(_,_) => true,
+            PositionalType::Optional(_,_) => false,
+        };
+
+        sig.insert_tagged(for_spec(arg.name(), "argument", is_required, tag));
+    }
+
+    if let Some(_) = signature.rest_positional {
+        let is_required = false;
+        sig.insert_tagged(for_spec("rest", "argument", is_required, tag));
+    }
+
+    for (name, ty) in signature.named.iter() {
+        match ty {
+            NamedType::Mandatory(_) => sig.insert_tagged(for_spec(name, "flag", true, tag)),
+            NamedType::Optional(_) => sig.insert_tagged(for_spec(name, "flag", false, tag)),
+            NamedType::Switch => sig.insert_tagged(for_spec(name, "switch", false, tag)),
+        }
+    }
+
+    sig.into_tagged_value()
+}

src/object/dict.rs

@@ -1,5 +1,4 @@
 use crate::prelude::*;
-
 use crate::object::{Primitive, Value};
 use derive_new::new;
 use indexmap::IndexMap;

src/parser/hir/baseline_parse_tokens.rs

@@ -49,6 +49,24 @@ pub enum SyntaxType {
     Boolean,
 }
 
+impl std::fmt::Display for SyntaxType {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        match self {
+            SyntaxType::Any => write!(f, "Any"),
+            SyntaxType::List => write!(f, "List"),
+            SyntaxType::Literal => write!(f, "Literal"),
+            SyntaxType::String => write!(f, "String"),
+            SyntaxType::Member => write!(f, "Member"),
+            SyntaxType::Variable => write!(f, "Variable"),
+            SyntaxType::Number => write!(f, "Number"),
+            SyntaxType::Path => write!(f, "Path"),
+            SyntaxType::Binary => write!(f, "Binary"),
+            SyntaxType::Block => write!(f, "Block"),
+            SyntaxType::Boolean => write!(f, "Boolean")
+        }
+    }
+}
+
 pub fn baseline_parse_next_expr(
     tokens: &mut TokensIterator,
     context: &Context,

src/parser/registry.rs

@@ -73,6 +73,8 @@ impl PositionalType {
 pub struct Signature {
     pub name: String,
     #[new(default)]
+    pub usage: String,
+    #[new(default)]
     pub positional: Vec<PositionalType>,
     #[new(value = "None")]
     pub rest_positional: Option<SyntaxType>,
@@ -87,6 +89,11 @@ impl Signature {
         Signature::new(name.into())
     }
 
+    pub fn desc(mut self, usage: impl Into<String>) -> Signature {
+        self.usage = usage.into();
+        self
+    }
+
     pub fn required(mut self, name: impl Into<String>, ty: impl Into<SyntaxType>) -> Signature {
         self.positional
             .push(PositionalType::Mandatory(name.into(), ty.into()));

src/plugins/add.rs

@@ -43,6 +43,7 @@ impl Add {
 impl Plugin for Add {
     fn config(&mut self) -> Result<Signature, ShellError> {
         Ok(Signature::build("add")
+            .desc("Add a new field to the table.")
             .required("Field", SyntaxType::String)
             .required("Value", SyntaxType::String)
             .rest(SyntaxType::String).filter())

src/plugins/binaryview.rs

@@ -12,7 +12,9 @@ impl BinaryView {
 
 impl Plugin for BinaryView {
     fn config(&mut self) -> Result<Signature, ShellError> {
-        Ok(Signature::build("binaryview").switch("lores"))
+        Ok(Signature::build("binaryview")
+            .desc("Autoview of binary data.")
+            .switch("lores"))
     }
 
     fn sink(&mut self, call_info: CallInfo, input: Vec<Tagged<Value>>) {

src/plugins/edit.rs

@@ -42,6 +42,7 @@ impl Edit {
 impl Plugin for Edit {
     fn config(&mut self) -> Result<Signature, ShellError> {
         Ok(Signature::build("edit")
+            .desc("Edit an existing field to have a new value.")
             .required("Field", SyntaxType::String)
             .required("Value", SyntaxType::String)
             .filter())

src/plugins/inc.rs

@@ -70,7 +70,7 @@ impl Inc {
         self.error = Some(message.to_string());
     }
 
-    fn usage(&self) -> &'static str {
+    pub fn usage() -> &'static str {
         "Usage: inc field [--major|--minor|--patch]"
     }
 
@@ -116,6 +116,7 @@ impl Inc {
 impl Plugin for Inc {
     fn config(&mut self) -> Result<Signature, ShellError> {
         Ok(Signature::build("inc")
+            .desc("Increment a value or version. Optional use the field of a table.")
             .switch("major")
             .switch("minor")
             .switch("patch")
@@ -159,7 +160,7 @@ impl Plugin for Inc {
 
         match &self.error {
             Some(reason) => {
-                return Err(ShellError::string(format!("{}: {}", reason, self.usage())))
+                return Err(ShellError::string(format!("{}: {}", reason, Inc::usage())))
             }
             None => Ok(vec![]),
         }

src/plugins/skip.rs

@@ -1,4 +1,3 @@
-use indexmap::IndexMap;
 use nu::{
     serve_plugin, CallInfo, Plugin, Primitive, ReturnSuccess, ReturnValue, ShellError, Signature,
     SyntaxType, Tagged, Value,
@@ -15,13 +14,10 @@ impl Skip {
 
 impl Plugin for Skip {
     fn config(&mut self) -> Result<Signature, ShellError> {
-        Ok(Signature {
-            name: "skip".to_string(),
-            positional: vec![],
-            is_filter: true,
-            named: IndexMap::new(),
-            rest_positional: Some(SyntaxType::Number),
-        })
+       Ok(Signature::build("skip")
+            .desc("Skip a number of rows")
+            .rest(SyntaxType::Number)
+            .filter())
     }
     fn begin_filter(&mut self, call_info: CallInfo) -> Result<Vec<ReturnValue>, ShellError> {
         if let Some(args) = call_info.args.positional {

src/plugins/str.rs

@@ -124,7 +124,7 @@ impl Str {
         }
     }
 
-    fn usage(&self) -> &'static str {
+    pub fn usage() -> &'static str {
         "Usage: str field [--downcase|--upcase|--to-int|--replace|--find-replace]"
     }
 }
@@ -154,7 +154,7 @@ impl Str {
                 None => Err(ShellError::string(format!(
                     "{}: {}",
                     "str needs a field when applying it to a value in an object",
-                    self.usage()
+                    Str::usage()
                 ))),
             },
             x => Err(ShellError::string(format!(
@@ -168,6 +168,7 @@ impl Str {
 impl Plugin for Str {
     fn config(&mut self) -> Result<Signature, ShellError> {
         Ok(Signature::build("str")
+            .desc("Apply string function. Optional use the field of a table")
             .switch("downcase")
             .switch("upcase")
             .switch("to-int")
@@ -240,7 +241,7 @@ impl Plugin for Str {
 
         match &self.error {
             Some(reason) => {
-                return Err(ShellError::string(format!("{}: {}", reason, self.usage())))
+                return Err(ShellError::string(format!("{}: {}", reason, Str::usage())))
             }
             None => Ok(vec![]),
         }

src/plugins/sum.rs

@@ -64,7 +64,9 @@ impl Sum {
 
 impl Plugin for Sum {
     fn config(&mut self) -> Result<Signature, ShellError> {
-        Ok(Signature::build("sum").filter())
+        Ok(Signature::build("sum")
+            .desc("Sum a column of values.")
+            .filter())
     }
 
     fn begin_filter(&mut self, _: CallInfo) -> Result<Vec<ReturnValue>, ShellError> {

src/plugins/sys.rs

@@ -309,7 +309,9 @@ async fn sysinfo(tag: Tag) -> Vec<Tagged<Value>> {
 
 impl Plugin for Sys {
     fn config(&mut self) -> Result<Signature, ShellError> {
-        Ok(Signature::build("sys").filter())
+        Ok(Signature::build("sys")
+            .desc("View information about the current system.")
+            .filter())
     }
 
     fn begin_filter(&mut self, callinfo: CallInfo) -> Result<Vec<ReturnValue>, ShellError> {

src/plugins/textview.rs

@@ -26,7 +26,8 @@ impl TextView {
 
 impl Plugin for TextView {
     fn config(&mut self) -> Result<Signature, ShellError> {
-        Ok(Signature::build("textview"))
+        Ok(Signature::build("textview")
+            .desc("Autoview of text data."))
     }
 
     fn sink(&mut self, call_info: CallInfo, input: Vec<Tagged<Value>>) {

src/plugins/tree.rs

@@ -80,7 +80,8 @@ struct TreeViewer;
 
 impl Plugin for TreeViewer {
     fn config(&mut self) -> Result<Signature, ShellError> {
-        Ok(Signature::build("tree"))
+        Ok(Signature::build("tree")
+            .desc("View the contents of the pipeline as a tree."))
     }
 
     fn sink(&mut self, _call_info: CallInfo, input: Vec<Tagged<Value>>) {

src/prelude.rs

@@ -68,6 +68,7 @@ pub(crate) use crate::parser::registry::Signature;
 pub(crate) use crate::shell::filesystem_shell::FilesystemShell;
 pub(crate) use crate::shell::shell_manager::ShellManager;
 pub(crate) use crate::shell::value_shell::ValueShell;
+pub(crate) use crate::shell::help_shell::HelpShell;
 pub(crate) use crate::stream::{InputStream, OutputStream};
 pub(crate) use crate::traits::{HasSpan, ToDebug};
 pub(crate) use crate::Span;

src/shell.rs

@@ -4,5 +4,6 @@ pub(crate) mod helper;
 pub(crate) mod shell;
 pub(crate) mod shell_manager;
 pub(crate) mod value_shell;
+pub(crate) mod help_shell;
 
 pub(crate) use helper::Helper;

src/shell/help_shell.rs

@@ -0,0 +1,234 @@
+use crate::commands::command::EvaluatedWholeStreamCommandArgs;
+use crate::commands::cp::CopyArgs;
+use crate::commands::mkdir::MkdirArgs;
+use crate::commands::mv::MoveArgs;
+use crate::commands::rm::RemoveArgs;
+use crate::context::SourceMap;
+use crate::object::{TaggedDictBuilder, command_dict};
+use crate::prelude::*;
+use crate::shell::shell::Shell;
+use std::ffi::OsStr;
+use std::path::PathBuf;
+
+#[derive(Clone, Debug)]
+pub struct HelpShell {
+    pub(crate) path: String,
+    pub(crate) value: Tagged<Value>,
+}
+
+impl HelpShell {
+    pub fn index(registry: &CommandRegistry) -> Result<HelpShell, std::io::Error> {
+        let mut cmds = TaggedDictBuilder::new(Tag::unknown());
+        let mut specs = Vec::new();
+
+        for cmd in registry.names() {
+            let mut spec = TaggedDictBuilder::new(Tag::unknown());
+            let value = command_dict(registry.get_command(&cmd).unwrap(), Tag::unknown());
+
+            spec.insert("name", cmd);
+            spec.insert("description", value.get_data_by_key("usage").unwrap().as_string().unwrap());
+            spec.insert_tagged("details", value);
+
+            specs.push(spec.into_tagged_value());
+        }
+
+        cmds.insert("help", Value::List(specs));
+
+        Ok(HelpShell {
+            path: "/help".to_string(),
+            value: cmds.into_tagged_value(),
+        })
+    }
+
+    pub fn for_command(
+        cmd: Tagged<Value>,
+        registry: &CommandRegistry,
+    ) -> Result<HelpShell, std::io::Error> {
+        let mut sh = HelpShell::index(&registry)?;
+
+        if let Tagged {
+            item: Value::Primitive(Primitive::String(name)), ..
+        } = cmd {
+            sh.set_path(format!("/help/{:}/details", name));
+        }
+
+        Ok(sh)
+    }
+
+    fn commands(&self) -> VecDeque<Tagged<Value>> {
+        let mut cmds = VecDeque::new();
+        let full_path = PathBuf::from(&self.path);
+
+        let mut viewed = self.value.clone();
+        let sep_string = std::path::MAIN_SEPARATOR.to_string();
+        let sep = OsStr::new(&sep_string);
+
+        for p in full_path.iter() {
+            match p {
+                x if x == sep => {}
+                step => match viewed.get_data_by_key(step.to_str().unwrap()) {
+                    Some(v) => {
+                        viewed = v.clone();
+                    }
+                    _ => {}
+                },
+            }
+        }
+        match viewed {
+            Tagged {
+                item: Value::List(l),
+                ..
+            } => {
+                for item in l {
+                    cmds.push_back(item.clone());
+                }
+            }
+            x => {
+                cmds.push_back(x.clone());
+            }
+        }
+
+        cmds
+    }
+}
+
+impl Shell for HelpShell {
+    fn name(&self, source_map: &SourceMap) -> String {
+        let origin_name = self.value.origin_name(source_map);
+        format!(
+            "{}",
+            match origin_name {
+                Some(x) => format!("{{{}}}", x),
+                None => format!("<{}>", self.value.item.type_name(),),
+            }
+        )
+    }
+
+    fn homedir(&self) -> Option<PathBuf> {
+        dirs::home_dir()
+    }
+
+    fn path(&self) -> String {
+        self.path.clone()
+    }
+
+    fn set_path(&mut self, path: String) {
+        let _ = std::env::set_current_dir(&path);
+        self.path = path.clone();
+    }
+
+    fn ls(&self, _args: EvaluatedWholeStreamCommandArgs) -> Result<OutputStream, ShellError> {
+        Ok(self
+            .commands()
+            .map(|x| ReturnSuccess::value(x))
+            .to_output_stream())
+    }
+
+    fn cd(&self, args: EvaluatedWholeStreamCommandArgs) -> Result<OutputStream, ShellError> {
+        let path = match args.nth(0) {
+            None => "/".to_string(),
+            Some(v) => {
+                let target = v.as_path()?;
+
+                let mut cwd = PathBuf::from(&self.path);
+
+                if target == PathBuf::from("..") {
+                    cwd.pop();
+                } else {
+                    match target.to_str() {
+                        Some(target) => match target.chars().nth(0) {
+                            Some(x) if x == '/' => cwd = PathBuf::from(target),
+                            _ => cwd.push(target),
+                        },
+                        None => cwd.push(target),
+                    }
+                }
+                cwd.to_string_lossy().to_string()
+            }
+        };
+
+        let mut stream = VecDeque::new();
+        stream.push_back(ReturnSuccess::change_cwd(path));
+        Ok(stream.into())
+    }
+
+    fn cp(&self, _args: CopyArgs, _name: Span, _path: &str) -> Result<OutputStream, ShellError> {
+        Ok(OutputStream::empty())
+    }
+
+    fn mv(&self, _args: MoveArgs, _name: Span, _path: &str) -> Result<OutputStream, ShellError> {
+        Ok(OutputStream::empty())
+    }
+
+    fn mkdir(
+        &self,
+        _args: MkdirArgs,
+        _name: Span,
+        _path: &str,
+    ) -> Result<OutputStream, ShellError> {
+        Ok(OutputStream::empty())
+    }
+
+    fn rm(&self, _args: RemoveArgs, _name: Span, _path: &str) -> Result<OutputStream, ShellError> {
+        Ok(OutputStream::empty())
+    }
+
+    fn complete(
+        &self,
+        line: &str,
+        pos: usize,
+        _ctx: &rustyline::Context<'_>,
+    ) -> Result<(usize, Vec<rustyline::completion::Pair>), rustyline::error::ReadlineError> {
+        let mut completions = vec![];
+
+        let mut possible_completion = vec![];
+        let commands = self.commands();
+        for cmd in commands {
+            match cmd {
+                Tagged { item, .. } => {
+                    for desc in item.data_descriptors() {
+                        possible_completion.push(desc);
+                    }
+                }
+            }
+        }
+
+        let line_chars: Vec<_> = line.chars().collect();
+        let mut replace_pos = pos;
+        while replace_pos > 0 {
+            if line_chars[replace_pos - 1] == ' ' {
+                break;
+            }
+            replace_pos -= 1;
+        }
+
+        for command in possible_completion.iter() {
+            let mut pos = replace_pos;
+            let mut matched = true;
+            if pos < line_chars.len() {
+                for chr in command.chars() {
+                    if line_chars[pos] != chr {
+                        matched = false;
+                        break;
+                    }
+                    pos += 1;
+                    if pos == line_chars.len() {
+                        break;
+                    }
+                }
+            }
+
+            if matched {
+                completions.push(rustyline::completion::Pair {
+                    display: command.to_string(),
+                    replacement: command.to_string(),
+                });
+            }
+        }
+        Ok((replace_pos, completions))
+    }
+
+    fn hint(&self, _line: &str, _pos: usize, _ctx: &rustyline::Context<'_>) -> Option<String> {
+        None
+    }
+}

src/shell/shell.rs

@@ -12,6 +12,7 @@ use std::path::PathBuf;
 pub trait Shell: std::fmt::Debug {
     fn name(&self, source_map: &SourceMap) -> String;
     fn homedir(&self) -> Option<PathBuf>;
+
     fn ls(&self, args: EvaluatedWholeStreamCommandArgs) -> Result<OutputStream, ShellError>;
     fn cd(&self, args: EvaluatedWholeStreamCommandArgs) -> Result<OutputStream, ShellError>;
     fn cp(&self, args: CopyArgs, name: Span, path: &str) -> Result<OutputStream, ShellError>;

tests/filters_test.rs

@@ -19,10 +19,10 @@ fn converts_structured_table_to_csv_text() {
         sandbox.with_files(vec![FileWithContentToBeTrimmed(
             "csv_text_sample.txt",
             r#"
-                    importer,shipper,tariff_item,name,origin
-                    Plasticos Rival,Reverte,2509000000,Calcium carbonate,Spain
-                    Tigre Ecuador,OMYA Andina,3824909999,Calcium carbonate,Colombia
-                "#,
+                importer,shipper,tariff_item,name,origin
+                Plasticos Rival,Reverte,2509000000,Calcium carbonate,Spain
+                Tigre Ecuador,OMYA Andina,3824909999,Calcium carbonate,Colombia
+            "#,
         )]);
 
         let actual = nu!(
@@ -49,10 +49,10 @@ fn converts_structured_table_to_csv_text_skipping_headers_after_conversion() {
         sandbox.with_files(vec![FileWithContentToBeTrimmed(
             "csv_text_sample.txt",
             r#"
-                    importer,shipper,tariff_item,name,origin
-                    Plasticos Rival,Reverte,2509000000,Calcium carbonate,Spain
-                    Tigre Ecuador,OMYA Andina,3824909999,Calcium carbonate,Colombia
-                "#,
+                importer,shipper,tariff_item,name,origin
+                Plasticos Rival,Reverte,2509000000,Calcium carbonate,Spain
+                Tigre Ecuador,OMYA Andina,3824909999,Calcium carbonate,Colombia
+            "#,
         )]);
 
         let actual = nu!(
@@ -75,19 +75,19 @@ fn converts_structured_table_to_csv_text_skipping_headers_after_conversion() {
 fn converts_from_csv_text_to_structured_table() {
     Playground::setup("filter_from_csv_test_1", |dirs, sandbox| {
         sandbox.with_files(vec![FileWithContentToBeTrimmed(
-            "los_tres_amigos.txt",
+            "los_tres_caballeros.txt",
             r#"
-                    first_name,last_name,rusty_luck
-                    Andrés,Robalino,1
-                    Jonathan,Turner,1
-                    Yehuda,Katz,1
-                "#,
+                first_name,last_name,rusty_luck
+                Andrés,Robalino,1
+                Jonathan,Turner,1
+                Yehuda,Katz,1
+            "#,
         )]);
 
         let actual = nu!(
             cwd: dirs.test(), h::pipeline(
             r#"
-                open los_tres_amigos.txt 
+                open los_tres_caballeros.txt 
                 | from-csv 
                 | get rusty_luck 
                 | str --to-int 
@@ -106,11 +106,11 @@ fn converts_from_csv_text_skipping_headers_to_structured_table() {
         sandbox.with_files(vec![FileWithContentToBeTrimmed(
             "los_tres_amigos.txt",
             r#"
-                    first_name,last_name,rusty_luck
-                    Andrés,Robalino,1
-                    Jonathan,Turner,1
-                    Yehuda,Katz,1
-                "#,
+                first_name,last_name,rusty_luck
+                Andrés,Robalino,1
+                Jonathan,Turner,1
+                Yehuda,Katz,1
+            "#,
         )]);
 
         let actual = nu!(
@@ -151,15 +151,15 @@ fn converts_from_json_text_to_structured_table() {
         sandbox.with_files(vec![FileWithContentToBeTrimmed(
             "katz.txt",
             r#"
-                    {
-                        "katz": [
-                            {"name":   "Yehuda", "rusty_luck": 1}, 
-                            {"name": "Jonathan", "rusty_luck": 1}, 
-                            {"name":   "Andres", "rusty_luck": 1},
-                            {"name":"GorbyPuff", "rusty_luck": 1}
-                        ]
-                    }
-                "#,
+                {
+                    "katz": [
+                        {"name":   "Yehuda", "rusty_luck": 1}, 
+                        {"name": "Jonathan", "rusty_luck": 1}, 
+                        {"name":   "Andres", "rusty_luck": 1},
+                        {"name":"GorbyPuff", "rusty_luck": 1}
+                    ]
+                }
+            "#,
         )]);
 
         let actual = nu!(
@@ -177,11 +177,11 @@ fn converts_from_json_text_recognizing_objects_independendtly_to_structured_tabl
         sandbox.with_files(vec![FileWithContentToBeTrimmed(
             "katz.txt",
             r#"
-                    {"name":   "Yehuda", "rusty_luck": 1} 
-                    {"name": "Jonathan", "rusty_luck": 1} 
-                    {"name":   "Andres", "rusty_luck": 1}
-                    {"name":"GorbyPuff", "rusty_luck": 3}
-                "#,
+                {"name":   "Yehuda", "rusty_luck": 1} 
+                {"name": "Jonathan", "rusty_luck": 1} 
+                {"name":   "Andres", "rusty_luck": 1}
+                {"name":"GorbyPuff", "rusty_luck": 3}
+            "#,
         )]);
 
         let actual = nu!(
@@ -205,9 +205,9 @@ fn converts_structured_table_to_json_text() {
         sandbox.with_files(vec![FileWithContentToBeTrimmed(
             "sample.txt",
             r#"
-                    JonAndrehudaTZ,3
-                    GorbyPuff,100
-                "#,
+                JonAndrehudaTZ,3
+                GorbyPuff,100
+            "#,
         )]);
 
         let actual = nu!(
@@ -245,10 +245,10 @@ fn converts_structured_table_to_tsv_text() {
         sandbox.with_files(vec![FileWithContentToBeTrimmed(
             "tsv_text_sample.txt",
             r#"
-                    importer	shipper	tariff_item	name	origin
-                    Plasticos Rival	Reverte	2509000000	Calcium carbonate	Spain
-                    Tigre Ecuador	OMYA Andina	3824909999	Calcium carbonate	Colombia
-                "#,
+                importer	shipper	tariff_item	name	origin
+                Plasticos Rival	Reverte	2509000000	Calcium carbonate	Spain
+                Tigre Ecuador	OMYA Andina	3824909999	Calcium carbonate	Colombia
+            "#,
         )]);
 
         let actual = nu!(
@@ -275,10 +275,10 @@ fn converts_structured_table_to_tsv_text_skipping_headers_after_conversion() {
         sandbox.with_files(vec![FileWithContentToBeTrimmed(
             "tsv_text_sample.txt",
             r#"
-                    importer    shipper tariff_item name    origin
-                    Plasticos Rival Reverte 2509000000  Calcium carbonate   Spain
-                    Tigre Ecuador   OMYA Andina 3824909999  Calcium carbonate   Colombia
-                "#,
+                importer    shipper tariff_item name    origin
+                Plasticos Rival Reverte 2509000000  Calcium carbonate   Spain
+                Tigre Ecuador   OMYA Andina 3824909999  Calcium carbonate   Colombia
+            "#,
         )]);
 
         let actual = nu!(
@@ -303,11 +303,11 @@ fn converts_from_tsv_text_to_structured_table() {
         sandbox.with_files(vec![FileWithContentToBeTrimmed(
             "los_tres_amigos.txt",
             r#"
-                    first Name	Last Name	rusty_luck
-                    Andrés	Robalino	1
-                    Jonathan	Turner	1
-                    Yehuda	Katz	1
-                "#,
+                first Name	Last Name	rusty_luck
+                Andrés	Robalino	1
+                Jonathan	Turner	1
+                Yehuda	Katz	1
+            "#,
         )]);
 
         let actual = nu!(
@@ -332,11 +332,11 @@ fn converts_from_tsv_text_skipping_headers_to_structured_table() {
         sandbox.with_files(vec![FileWithContentToBeTrimmed(
             "los_tres_amigos.txt",
             r#"
-                    first Name	Last Name	rusty_luck
-                    Andrés	Robalino	1
-                    Jonathan	Turner	1
-                    Yehuda	Katz	1
-                "#,
+                first Name	Last Name	rusty_luck
+                Andrés	Robalino	1
+                Jonathan	Turner	1
+                Yehuda	Katz	1
+            "#,
         )]);
 
         let actual = nu!(
@@ -359,14 +359,15 @@ fn converts_from_tsv_text_skipping_headers_to_structured_table() {
 fn can_convert_table_to_bson_and_back_into_table() {
     let actual = nu!(
         cwd: "tests/fixtures/formats", h::pipeline(
-            r#"
-               open sample.bson
-               | to-bson
-               | from-bson
-               | get root
-               | nth 1
-               | get b
-               | echo $it"#
+        r#"
+            open sample.bson
+            | to-bson
+            | from-bson
+            | get root
+            | nth 1
+            | get b
+            | echo $it
+        "#
     ));
 
     assert_eq!(actual, "whel");
@@ -376,14 +377,15 @@ fn can_convert_table_to_bson_and_back_into_table() {
 fn can_convert_table_to_sqlite_and_back_into_table() {
     let actual = nu!(
         cwd: "tests/fixtures/formats", h::pipeline(
-             r#"
-                 open sample.db
-                 | to-sqlite
-                 | from-sqlite
-                 | get table_values
-                 | nth 2
-                 | get x
-                 | echo $it"#
+        r#"
+            open sample.db
+            | to-sqlite
+            | from-sqlite
+            | get table_values
+            | nth 2
+            | get x
+            | echo $it
+        "#
     ));
 
     assert_eq!(actual, "hello");
@@ -393,12 +395,13 @@ fn can_convert_table_to_sqlite_and_back_into_table() {
 fn can_convert_table_to_toml_text_and_from_toml_text_back_into_table() {
     let actual = nu!(
         cwd: "tests/fixtures/formats", h::pipeline(
-            r#"
-                open cargo_sample.toml
-                | to-toml
-                | from-toml
-                | get package.name
-                | echo $it"#
+        r#"
+            open cargo_sample.toml
+            | to-toml
+            | from-toml
+            | get package.name
+            | echo $it
+        "#
     ));
 
     assert_eq!(actual, "nu");