Merge pull request #555 from nushell/help

Help baseline.

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");