implement capturing groups

README.md

@@ -9,12 +9,37 @@ something that is not easy to achieve with tools like `grep` and `less`.
 # Usage
 ```
 Usage: colorexp [options] patterns...
--F, --fixed-strings   Don't interpret regular expression metacharacters.
--H, --highlight       Color by changing the background color.
--i, --ignore-case     Perform case insensitive matching.
+  -F, --fixed-strings           Do not interpret regular expression metacharacters.
+  -H, --highlight               Color by changing the background color. The default is to change the foreground color.
+  -i, --ignore-case             Perform case insensitive matching.
+  -g, --vary-group-colors-off   Turn off changing of colors for every capturing group. Defaults to on if exactly one pattern is given.
+  -G, --vary-group-colors-on    Turn on changing of colors for every capturing group. Defaults to on if exactly one pattern is given.
 ```
-## Example
-![Example](example.png)
+## Examples
+
+### Basic Usage
+- use the `-H` option to colorize the background, instead of the text
+
+![Example](example-basic.png)
+
+### Overlapping matches - last match wins
+- all matches are colorized, and the color of the last match will be used
+
+![Example](example-overlaps.png)
+
+### Capturing groups
+- when using capturing groups, only the matched group contents will be colorized
+#### Vary colors of groups in patterns
+- when exactly one pattern is given, the default is to use different colors for each capturing group
+  - in case of multiple patterns, the `-G` option can be used to enforce varying of the colors for each group
+
+![Example](example-group-varying-colors.png)
+
+#### Use the same color for all groups of a pattern
+- when multiple patterns are given, the default is to use the same colors for all capturing groups of a pattern
+    - in case of a single pattern, the `-g` option can be used to enforce use of a single color
+
+![Example](example-group-same-colors.png)
 
 # Installation
 

colorexp.go

@@ -8,7 +8,7 @@ import (
 	"regexp"
 )
 
-const version = "1.0.4"
+const version = "1.0.5"
 
 var foregroundColors = []string{
 	//"\033[30m", // Black
@@ -91,13 +91,31 @@ func addRange(ranges []rangeWithID, newRange rangeWithID) []rangeWithID {
 	return result
 }
 
-func match(line string, regexps []*regexp.Regexp) []rangeWithID {
+func match(line string, regexps []*regexp.Regexp, varyGroupColors bool) []rangeWithID {
 	var ranges []rangeWithID
-	for colorIdx, re := range regexps {
-		matchRanges := re.FindAllStringIndex(line, -1)
+	colorIdx := 0
+	for _, re := range regexps {
+		numGroups := re.NumSubexp()
+		matchRanges := re.FindAllStringSubmatchIndex(line, -1)
+		firstGroupToColorize := min(1, numGroups)
+		groupsToColorize := numGroups + 1 - firstGroupToColorize
 		for _, matchRange := range matchRanges {
-			ranges = addRange(ranges, rangeWithID{matchRange[0], matchRange[1], colorIdx})
+			// if there is no capturing group, the full match will be colorized (group 0)
+			// if there are capturing groups, all groups but group 0 (the full match) will be colorized
+			for i := 0; i < groupsToColorize; i++ {
+				curColorIdx := colorIdx
+				if varyGroupColors {
+					curColorIdx += i
+				}
+				gIdx := (i + firstGroupToColorize) * 2
+				matchRangeStart := matchRange[gIdx]
+				matchRangeEnd := matchRange[gIdx+1]
+				if matchRangeEnd > matchRangeStart {
+					ranges = addRange(ranges, rangeWithID{matchRangeStart, matchRangeEnd, curColorIdx})
+				}
+			}
 		}
+		colorIdx += groupsToColorize
 	}
 	return ranges
 }
@@ -127,11 +145,14 @@ func printUsage() {
 
 func main() {
 	var (
-		fixedStrings bool
-		showHelp     bool
-		highlight    bool
-		ignoreCase   bool
-		showVersion  bool
+		fixedStrings       bool
+		showHelp           bool
+		highlight          bool
+		ignoreCase         bool
+		showVersion        bool
+		varyGroupColorsOn  bool
+		varyGroupColorsOff bool
+		varyGroupColors    bool
 	)
 
 	pflag.BoolVarP(&fixedStrings, "fixed-strings", "F", false, "Do not interpret regular expression metacharacters.")
@@ -140,6 +161,9 @@ func main() {
 	pflag.BoolVarP(&ignoreCase, "ignore-case", "i", false, "Perform case insensitive matching.")
 	pflag.BoolVarP(&showVersion, "version", "V", false, "Display version information and exit.")
 
+	pflag.BoolVarP(&varyGroupColorsOn, "vary-group-colors-on", "G", false, "Turn on changing of colors for every capturing group. Defaults to on if exactly one pattern is given.")
+	pflag.BoolVarP(&varyGroupColorsOff, "vary-group-colors-off", "g", false, "Turn off changing of colors for every capturing group. Defaults to on if exactly one pattern is given.")
+
 	pflag.Parse()
 
 	if showVersion {
@@ -155,11 +179,24 @@ func main() {
 	regexStrings := pflag.Args()
 
 	if len(regexStrings) == 0 {
-		_, _ = fmt.Println("Error: At least one pattern argument is required.")
+		_, _ = fmt.Println("Error: At least one pattern argument is required.\n")
 		printUsage()
 		os.Exit(1)
 	}
 
+	if pflag.Lookup("vary-group-colors-on").Changed {
+		if pflag.Lookup("vary-group-colors-off").Changed {
+			_, _ = fmt.Println("Error: -G/-g arguments cannot both be used at the same time.\n")
+			printUsage()
+			os.Exit(1)
+		}
+		varyGroupColors = true
+	} else if pflag.Lookup("vary-group-colors-off").Changed {
+		varyGroupColors = false
+	} else {
+		varyGroupColors = len(regexStrings) == 1
+	}
+
 	// Note that the order in regexps is the reverse of the original order, to implement the "last regexp wins" logic
 	var regexps []*regexp.Regexp
 	for _, regexString := range regexStrings {
@@ -174,7 +211,8 @@ func main() {
 			_, _ = fmt.Printf("Invalid regular expression: %v\n", err)
 			os.Exit(1)
 		}
-		// insert at the beginning of the slice, to revert the order
+		// insert at the beginning of the slice, to invert the order,
+		// so that the last regex takes precedence
 		regexps = append([]*regexp.Regexp{re}, regexps...)
 	}
 
@@ -191,7 +229,7 @@ func main() {
 	scanner := bufio.NewScanner(os.Stdin)
 	for scanner.Scan() {
 		line := scanner.Text()
-		ranges := match(line, regexps)
+		ranges := match(line, regexps, varyGroupColors)
 		colorizedLine := colorize(line, colors, resetColor, ranges)
 		fmt.Println(colorizedLine)
 	}