support for reading from file rather than stdin

Signed-off-by: Alex Couture-Beil <alex@mofo.ca>

.golangci.yaml

@@ -0,0 +1,2 @@
+run:
+  timeout: 10m

cmd/main.go

@@ -5,6 +5,8 @@ import (
 	"fmt"
 	"os"
 	"regexp"
+	"sort"
+	"strings"
 )
 
 type pattern struct {
@@ -17,6 +19,55 @@ func die(msg string, args ...interface{}) {
 	os.Exit(1)
 }
 
+const nc = "\033[0m"
+
+var (
+	colors        map[string]string
+	defaultColors []string
+	colorOptions  string
+)
+
+func init() {
+	colors = map[string]string{
+		"red":         "\033[0;31m",
+		"green":       "\033[0;32m",
+		"orange":      "\033[0;33m",
+		"blue":        "\033[0;34m",
+		"purple":      "\033[0;35m",
+		"cyan":        "\033[0;36m",
+		"lightgray":   "\033[0;37m",
+		"darkgray":    "\033[1;30m",
+		"lightred":    "\033[1;31m",
+		"lightgreen":  "\033[1;32m",
+		"yellow":      "\033[1;33m",
+		"lightblue":   "\033[1;34m",
+		"lightpurple": "\033[1;35m",
+		"lightcyan":   "\033[1;36m",
+	}
+	l := []string{}
+	for c := range colors {
+		l = append(l, c)
+	}
+	sort.Strings(l)
+	colorOptions = strings.Join(l, ", ")
+
+	defaultColors = []string{
+		colors["red"],
+		colors["green"],
+		colors["orange"],
+		colors["blue"],
+		colors["purple"],
+		colors["cyan"],
+		colors["yellow"],
+		colors["lightred"],
+		colors["lightgreen"],
+		colors["lightblue"],
+		colors["lightpurple"],
+		colors["lightcyan"],
+	}
+
+}
+
 func main() {
 	progName := "colorgrep"
 	if len(os.Args) > 0 {
@@ -29,6 +80,9 @@ func main() {
 	wordBoundary := false
 	showHelp := false
 	colorNext := false
+	fileNext := false
+	file := ""
+	fileGiven := false
 	var color string
 	for _, arg := range os.Args[1:] {
 		if len(arg) == 0 {
@@ -39,7 +93,17 @@ func main() {
 			colorNext = false
 			continue
 		}
+		if fileGiven {
+			die("only a single file can be specified\n")
+		}
+		if fileNext {
+			file = arg
+			fileGiven = true
+			fileNext = false
+			continue
+		}
 		if arg[0] == '-' && !ignoreDashes {
+		shortFor:
 			for _, short := range arg[1:] {
 				switch short {
 				case 'h':
@@ -58,6 +122,16 @@ func main() {
 					wordBoundary = true
 				case 'e':
 					ignoreDashes = true
+				case '-':
+					switch arg[2:] {
+					case "help":
+						showHelp = true
+					case "":
+						fileNext = true
+					default:
+						die("Error: %s not recognized\n", arg)
+					}
+					break shortFor
 				default:
 					die("Error: -%c not recognized\n", short)
 				}
@@ -86,54 +160,34 @@ func main() {
 
 	if showHelp {
 		fmt.Printf(
-			"%s [options] <pattern> [[-i] [-w] [-c <color>] <pattern> [...]]\n"+
+			"usage: %s [options] <pattern> [[-i] [-w] [-c <color>] <pattern> [...]] [-- <file>]\n"+
+				"\n"+
+				"Reads from stdin (or <file> when specified), any regex patterns which match will cause the text to be highlighted.\n"+
+				"\n"+
 				"  -i           case insensitive matching\n"+
 				"  -w           word boundary matching\n"+
-				"  -c <color>   color to highlight match\n"+
+				"  -c <color>   color to highlight match: %s\n"+
 				"  -e <pattern> use pattern (useful for patterns starting with a hyphen)\n"+
-				"  -h, --help   display this help\n", progName)
+				"  -h, --help   display this help\n", progName, colorOptions)
 		os.Exit(0)
 	}
 
-	colors := map[string]string{
-		"red":         "\033[0;31m",
-		"green":       "\033[0;32m",
-		"orange":      "\033[0;33m",
-		"blue":        "\033[0;34m",
-		"purple":      "\033[0;35m",
-		"cyan":        "\033[0;36m",
-		"lightgray":   "\033[0;37m",
-		"darkgray":    "\033[1;30m",
-		"lightred":    "\033[1;31m",
-		"lightgreen":  "\033[1;32m",
-		"yellow":      "\033[1;33m",
-		"lightblue":   "\033[1;34m",
-		"lightpurple": "\033[1;35m",
-		"lightcyan":   "\033[1;36m",
-	}
-	nc := "\033[0m"
-
-	defaultColors := []string{
-		colors["red"],
-		colors["green"],
-		colors["orange"],
-		colors["blue"],
-		colors["purple"],
-		colors["cyan"],
-		colors["yellow"],
-		colors["lightred"],
-		colors["lightgreen"],
-		colors["lightblue"],
-		colors["lightpurple"],
-		colors["lightcyan"],
-	}
-
 	getColor := func(i int) string {
 		n := len(defaultColors)
 		return defaultColors[i%n]
 	}
 
-	scanner := bufio.NewScanner(os.Stdin)
+	var scanner *bufio.Scanner
+	if fileGiven {
+		fileHandle, err := os.Open(file)
+		if err != nil {
+			die("failed to open %s: %s\n", file, err.Error())
+		}
+		defer fileHandle.Close()
+		scanner = bufio.NewScanner(bufio.NewReader(fileHandle))
+	} else {
+		scanner = bufio.NewScanner(os.Stdin)
+	}
 	for scanner.Scan() {
 		l := scanner.Text()
 		for i, pat := range patterns {
@@ -142,7 +196,7 @@ func main() {
 				var ok bool
 				col, ok = colors[pat.color]
 				if !ok {
-					die("color %s not found", pat.color)
+					die("color %s not found\n", pat.color)
 				}
 			}
 			l = pat.re.ReplaceAllString(l, col+"$0"+nc)