show usage of program (closes #3)

README.md

@@ -97,7 +97,7 @@ are not followed by colouring arguments are coloured based on previously
 provided colour:
 
 ```bash
-$ blush -b match1 match3 FILENAME
+$ blush -b match1 match2 FILENAME
 ```
 
 ![Colored](http://i.imgur.com/J6uZPQD.png)

cmd/helper_test.go

@@ -56,18 +56,21 @@ func setup(t *testing.T, args string) (stdout, stderr *stdFile, cleanup func())
 	if len(args) > 1 {
 		os.Args = append(os.Args, strings.Split(args, " ")...)
 	}
-	logFatalErr := func(msg ...interface{}) {
+	fatalPatch := monkey.Patch(log.Fatal, func(msg ...interface{}) {
 		fmt.Fprintln(os.Stderr, msg)
-	}
-	patch := monkey.Patch(log.Fatal, logFatalErr)
+	})
+	fatalfPatch := monkey.Patch(log.Fatalf, func(format string, v ...interface{}) {
+		fmt.Fprintf(os.Stderr, format, v...)
+	})
 
 	cleanup = func() {
 		outCleanup()
 		errCleanup()
 		os.Args = oldArgs
 		os.Stdout = oldStdout
 		os.Stderr = oldStderr
-		patch.Unpatch()
+		fatalPatch.Unpatch()
+		fatalfPatch.Unpatch()
 	}
 	return stdout, stderr, cleanup
 }

cmd/main.go

@@ -1,6 +1,7 @@
 package cmd
 
 import (
+	"fmt"
 	"io"
 	"log"
 	"os"
@@ -16,8 +17,13 @@ import (
 // blush.Blush instance. It then uses io.Copy() to write to standard output.
 func Main() {
 	b, err := GetBlush(os.Args)
-	if err != nil {
-		log.Fatal(err)
+	switch err {
+	case nil:
+	case errShowHelp:
+		fmt.Println(Usage)
+		return
+	default:
+		log.Fatalf("%s\n%s", err, Help)
 		return // this return statement should be here to support tests.
 	}
 	defer func() {
@@ -43,11 +49,18 @@ func GetBlush(input []string) (*blush.Blush, error) {
 		ok         bool
 		noCut      bool
 		noFileName bool
+		remaining  []string
+		err        error
+		r          io.ReadCloser
 	)
 	if len(input) == 1 {
 		return nil, ErrNoInput
 	}
-	remaining, r, err := getReader(input[1:])
+	if remaining, ok = hasArg(input[1:], "--help"); ok {
+		return nil, errShowHelp
+	}
+
+	remaining, r, err = getReader(remaining)
 	if err != nil {
 		return nil, err
 	}

cmd/main_test.go

@@ -21,6 +21,21 @@ func TestMainNoArgs(t *testing.T) {
 	if !strings.Contains(stderr.String(), cmd.ErrNoInput.Error()) {
 		t.Errorf("stderr = `%s`, want `%s` in it", stderr.String(), cmd.ErrNoInput.Error())
 	}
+	if !strings.Contains(stderr.String(), cmd.Help) {
+		t.Errorf("stderr = `%s`, want `%s` in it", stderr.String(), cmd.Help)
+	}
+}
+
+func TestMainHelp(t *testing.T) {
+	stdout, stderr, cleanup := setup(t, "--help")
+	defer cleanup()
+	cmd.Main()
+	if len(stderr.String()) > 0 {
+		t.Errorf("didn't expect any stderr, got: %s", stderr.String())
+	}
+	if !strings.Contains(stdout.String(), cmd.Usage) {
+		t.Errorf("stdout = `%s`, want `%s` in it", stdout.String(), cmd.Usage)
+	}
 }
 
 func TestPipeInput(t *testing.T) {

cmd/usage.go

@@ -0,0 +1,46 @@
+package cmd
+
+import "errors"
+
+// These variables are used for showing help messages on command line.
+var (
+	errShowHelp = errors.New("show errors")
+
+	Help  = "Usage: blush [OPTION]... PATTERN [FILE]...\nTry 'blush --help' for more information."
+	Usage = `Usage: blush [OPTION]... PATTERN [FILE]...
+Colours:
+    -r, --red       Match decorated with red colour. See Stock Colours section.
+    -r[G], --red[G] Matches are grouped with the group number.
+                    Example: blush -b1 match filename
+    -#RGB, --#RGB   Use user defined colour schemas.
+                    Example: blush -#1eF match filename
+    -#RRGGBB, --#RRGGBB Same as -#RGB/--#RGB.
+
+Pattern:
+    You can use simple pattern or regexp. If your pattern expands between
+    multiple words or has space in between, you should put them in quotations.
+
+Stock Colours:
+    -r, --red
+    -g, --green
+    -b, --blue
+    -w, --white
+    -bl, --black
+    -yl, --yellow
+    -mg, --magenta
+    -cy, --cyan
+
+
+Control arguments:
+    -C, --colour            Don't drop unmatched lines.
+    -i                      Case insensitive match.
+    --no-colour, --no-color Don't colourise the output.
+    -h, --no-filename       Suppress the prefixing of file names on output.
+
+Multi match colouring:
+    blush -b match1 [match2]...: will colourise all matches with the same colour.
+
+Using pipes:
+    cat FILE | blush -b match [-g match]...
+`
+)