Support help op, add color to error

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>

cmd/kubectx/help.go

@@ -0,0 +1,24 @@
+package main
+
+import (
+	"fmt"
+	"io"
+)
+
+func printHelp(out io.Writer) {
+	help := `USAGE:
+  kubectx                       : list the contexts
+  kubectx <NAME>                : switch to context <NAME>
+  kubectx -                     : switch to the previous context
+  kubectx -c, --current         : show the current context name
+  kubectx <NEW_NAME>=<NAME>     : rename context <NAME> to <NEW_NAME>
+  kubectx <NEW_NAME>=.          : rename current-context to <NEW_NAME>
+  kubectx -d <NAME> [<NAME...>] : delete context <NAME> ('.' for current-context)
+                                  (this command won't delete the user/cluster entry
+                                  that is used by the context)
+  kubectx -u, --unset           : unset the current context
+
+  kubectx -h,--help             : show this message`
+
+	fmt.Fprintf(out, "%s\n", help)
+}

cmd/kubectx/help_test.go

@@ -0,0 +1,21 @@
+package main
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+)
+
+func TestPrintHelp(t *testing.T) {
+	var buf bytes.Buffer
+	printHelp(&buf)
+
+	out := buf.String()
+	if !strings.Contains(out, "USAGE:") {
+		t.Errorf("help string doesn't contain USAGE: ; output=%q", out)
+	}
+
+	if !strings.HasSuffix(out, "\n") {
+		t.Errorf("does not end with new line; output=%q", out)
+	}
+}

cmd/kubectx/main.go

@@ -4,6 +4,8 @@ import (
 	"fmt"
 	"os"
 	"strings"
+
+	"github.com/fatih/color"
 )
 
 func main() {
@@ -12,6 +14,8 @@ func main() {
 	op = parseArgs(os.Args[1:])
 
 	switch v := op.(type) {
+	case HelpOp:
+		printHelp(os.Stdout)
 	case ListOp:
 		// TODO implement
 		panic("not implemented")
@@ -19,8 +23,10 @@ func main() {
 		// TODO implement
 		panic("not implemented")
 	case UnknownOp:
-		fmt.Printf("error: unsupported operation: %s\n", strings.Join(v.Args, " "))
+		fmt.Printf("%s unsupported operation: %s\n",
-		// TODO print --help string
+			color.RedString("error:"),
+			strings.Join(v.Args, " "))
+		printHelp(os.Stdout)
 		os.Exit(1)
 	default:
 		fmt.Printf("internal error: operation type %T not handled", op)

go.mod

@@ -2,4 +2,7 @@ module github.com/ahmetb/kubectx
 
 go 1.14
 
-require github.com/google/go-cmp v0.4.0
+require (
+	github.com/fatih/color v1.9.0
+	github.com/google/go-cmp v0.4.0
+)

go.sum

@@ -1,3 +1,13 @@
+github.com/fatih/color v1.9.0 h1:8xPHl4/q1VyqGIPif1F+1V3Y3lSmrq01EabUW3CoW5s=
+github.com/fatih/color v1.9.0/go.mod h1:eQcE1qtQxscV5RaZvpXrrb8Drkc3/DdQ+uUYCNjL+zU=
 github.com/google/go-cmp v0.4.0 h1:xsAVV57WRhGj6kEIi8ReJzQlHHqcBYCElAvkovg3B/4=
 github.com/google/go-cmp v0.4.0/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+github.com/mattn/go-colorable v0.1.4 h1:snbPLB8fVfU9iwbbo30TPtbLRzwWu6aJS6Xh4eaaviA=
+github.com/mattn/go-colorable v0.1.4/go.mod h1:U0ppj6V5qS13XJ6of8GYAs25YV2eR4EVcfRqFIhoBtE=
+github.com/mattn/go-isatty v0.0.8/go.mod h1:Iq45c/XA43vh69/j3iqttzPXn0bhXyGjM0Hdxcsrc5s=
+github.com/mattn/go-isatty v0.0.11 h1:FxPOTFNqGkuDUGi3H/qkUbQO4ZiBa2brKq5r0l8TGeM=
+github.com/mattn/go-isatty v0.0.11/go.mod h1:PhnuNfih5lzO57/f3n+odYbM4JtupLOxQOAqxQCu2WE=
+golang.org/x/sys v0.0.0-20190222072716-a9d3bda3a223/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20191026070338-33540a1f6037 h1:YyJpGZS1sBuBCzLAR1VEpK193GlqGZbnPFnPV/5Rsb4=
+golang.org/x/sys v0.0.0-20191026070338-33540a1f6037/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=