Add a batch of help examples (#1759)

crates/nu-cli/src/commands/config.rs

@@ -72,6 +72,39 @@ impl WholeStreamCommand for Config {
     ) -> Result<OutputStream, ShellError> {
         args.process(registry, config)?.run()
     }
+
+    fn examples(&self) -> &[Example] {
+        &[
+            Example {
+                description: "See all config values",
+                example: "config",
+            },
+            Example {
+                description: "Set completion_mode to circular",
+                example: "config --set [completion_mode circular]",
+            },
+            Example {
+                description: "Store the contents of the pipeline as a path",
+                example: "echo ['/usr/bin' '/bin'] | config --set_into path",
+            },
+            Example {
+                description: "Get the current startup commands",
+                example: "config --get startup",
+            },
+            Example {
+                description: "Remove the startup commands",
+                example: "config --remove startup",
+            },
+            Example {
+                description: "Clear the config (be careful!)",
+                example: "config --clear",
+            },
+            Example {
+                description: "Get the path to the current config file",
+                example: "config --path",
+            },
+        ]
+    }
 }
 
 pub fn config(

crates/nu-cli/src/commands/cp.rs

@@ -42,6 +42,19 @@ impl WholeStreamCommand for Cpy {
     ) -> Result<OutputStream, ShellError> {
         args.process(registry, cp)?.run()
     }
+
+    fn examples(&self) -> &[Example] {
+        &[
+            Example {
+                description: "Copy myfile to dir_b",
+                example: "cp myfile dir_b",
+            },
+            Example {
+                description: "Recursively copy dir_a to dir_b",
+                example: "cp -r dir_a dir_b",
+            },
+        ]
+    }
 }
 
 pub fn cp(args: CopyArgs, context: RunnableContext) -> Result<OutputStream, ShellError> {

crates/nu-cli/src/commands/default.rs

@@ -40,6 +40,13 @@ impl WholeStreamCommand for Default {
     ) -> Result<OutputStream, ShellError> {
         args.process(registry, default)?.run()
     }
+
+    fn examples(&self) -> &[Example] {
+        &[Example {
+            description: "Give a default 'target' to all file entries",
+            example: "ls -af | default target 'nothing'",
+        }]
+    }
 }
 
 fn default(

crates/nu-cli/src/commands/drop.rs

@@ -36,6 +36,19 @@ impl WholeStreamCommand for Drop {
     ) -> Result<OutputStream, ShellError> {
         args.process(registry, drop)?.run()
     }
+
+    fn examples(&self) -> &[Example] {
+        &[
+            Example {
+                description: "Remove the last item of a list/table",
+                example: "echo [1 2 3] | drop",
+            },
+            Example {
+                description: "Remove the last 2 items of a list/table",
+                example: "echo [1 2 3] | drop 2",
+            },
+        ]
+    }
 }
 
 fn drop(DropArgs { rows }: DropArgs, context: RunnableContext) -> Result<OutputStream, ShellError> {

crates/nu-cli/src/commands/du.rs

@@ -78,6 +78,13 @@ impl WholeStreamCommand for Du {
     ) -> Result<OutputStream, ShellError> {
         args.process(registry, du)?.run()
     }
+
+    fn examples(&self) -> &[Example] {
+        &[Example {
+            description: "Disk usage of the current directory",
+            example: "du *",
+        }]
+    }
 }
 
 fn du(args: DuArgs, ctx: RunnableContext) -> Result<OutputStream, ShellError> {

crates/nu-cli/src/commands/each.rs

@@ -41,6 +41,13 @@ impl WholeStreamCommand for Each {
     ) -> Result<OutputStream, ShellError> {
         Ok(args.process_raw(registry, each)?.run())
     }
+
+    fn examples(&self) -> &[Example] {
+        &[Example {
+            description: "Print the name of each file",
+            example: "ls | each { echo $it.name }",
+        }]
+    }
 }
 
 fn is_expanded_it_usage(head: &SpannedExpression) -> bool {

crates/nu-cli/src/commands/echo.rs

@@ -30,6 +30,19 @@ impl WholeStreamCommand for Echo {
     ) -> Result<OutputStream, ShellError> {
         args.process(registry, echo)?.run()
     }
+
+    fn examples(&self) -> &[Example] {
+        &[
+            Example {
+                description: "Put a hello message in the pipeline",
+                example: "echo 'hello'",
+            },
+            Example {
+                description: "Print the value of the special '$nu' variable",
+                example: "echo $nu",
+            },
+        ]
+    }
 }
 
 fn echo(args: EchoArgs, _: RunnableContext) -> Result<OutputStream, ShellError> {

crates/nu-cli/src/commands/enter.rs

@@ -40,6 +40,19 @@ impl WholeStreamCommand for Enter {
     ) -> Result<OutputStream, ShellError> {
         Ok(args.process_raw(registry, enter)?.run())
     }
+
+    fn examples(&self) -> &[Example] {
+        &[
+            Example {
+                description: "Enter a path as a new shell",
+                example: "enter ../projectB",
+            },
+            Example {
+                description: "Enter a file as a new shell",
+                example: "enter package.json",
+            },
+        ]
+    }
 }
 
 fn enter(

crates/nu-cli/src/commands/exit.rs

@@ -26,6 +26,19 @@ impl WholeStreamCommand for Exit {
     ) -> Result<OutputStream, ShellError> {
         exit(args, registry)
     }
+
+    fn examples(&self) -> &[Example] {
+        &[
+            Example {
+                description: "Exit the current shell",
+                example: "exit",
+            },
+            Example {
+                description: "Exit all shells (exiting Nu)",
+                example: "exit --now",
+            },
+        ]
+    }
 }
 
 pub fn exit(args: CommandArgs, registry: &CommandRegistry) -> Result<OutputStream, ShellError> {

crates/nu-cli/src/commands/first.rs

@@ -36,6 +36,19 @@ impl WholeStreamCommand for First {
     ) -> Result<OutputStream, ShellError> {
         args.process(registry, first)?.run()
     }
+
+    fn examples(&self) -> &[Example] {
+        &[
+            Example {
+                description: "Return the first item of a list/table",
+                example: "echo [1 2 3] | first",
+            },
+            Example {
+                description: "Return the first 2 items of a list/table",
+                example: "echo [1 2 3] | first 2",
+            },
+        ]
+    }
 }
 
 fn first(

crates/nu-cli/src/commands/format.rs

@@ -38,6 +38,13 @@ impl WholeStreamCommand for Format {
     ) -> Result<OutputStream, ShellError> {
         args.process(registry, format_command)?.run()
     }
+
+    fn examples(&self) -> &[Example] {
+        &[Example {
+            description: "Print filenames with their sizes",
+            example: "ls | format '{name}: {size}'",
+        }]
+    }
 }
 
 fn format_command(

crates/nu-cli/src/commands/from_bson.rs

@@ -28,6 +28,13 @@ impl WholeStreamCommand for FromBSON {
     ) -> Result<OutputStream, ShellError> {
         from_bson(args, registry)
     }
+
+    fn examples(&self) -> &[Example] {
+        &[Example {
+            description: "Convert bson data to a table",
+            example: "open file.bin | from bson",
+        }]
+    }
 }
 
 fn bson_array(input: &[Bson], tag: Tag) -> Result<Vec<Value>, ShellError> {

crates/nu-cli/src/commands/from_csv.rs

@@ -43,6 +43,23 @@ impl WholeStreamCommand for FromCSV {
     ) -> Result<OutputStream, ShellError> {
         args.process(registry, from_csv)?.run()
     }
+
+    fn examples(&self) -> &[Example] {
+        &[
+            Example {
+                description: "Convert comma-separated data to a table",
+                example: "open data.txt | from csv",
+            },
+            Example {
+                description: "Convert comma-separated data to a table, ignoring headers",
+                example: "open data.txt | from csv --headerless",
+            },
+            Example {
+                description: "Convert semicolon-separated data to a table",
+                example: "open data.txt | from csv --separator ';'",
+            },
+        ]
+    }
 }
 
 fn from_csv(