added support for regexp in -c parameter, added deduplication as well

lib/helpers.go

@@ -36,22 +36,56 @@ func contains(s []int, e int) bool {
 	return false
 }
 
-func PrepareColumns() error {
+// parse columns list given with -c
+func PrepareColumns(data *Tabdata) error {
+	UseColumns = nil
 	if len(Columns) > 0 {
 		for _, use := range strings.Split(Columns, ",") {
-			usenum, err := strconv.Atoi(use)
-			if err != nil {
-				msg := fmt.Sprintf("Could not parse columns list %s: %v", Columns, err)
+			if len(use) == 0 {
+				msg := fmt.Sprintf("Could not parse columns list %s: empty column", Columns)
 				return errors.New(msg)
 			}
-			UseColumns = append(UseColumns, usenum)
+
+			usenum, err := strconv.Atoi(use)
+			if err != nil {
+				// might be a regexp
+				colPattern, err := regexp.Compile(use)
+				if err != nil {
+					msg := fmt.Sprintf("Could not parse columns list %s: %v", Columns, err)
+					return errors.New(msg)
+				}
+
+				// find matching header fields
+				for i, head := range data.headers {
+					if colPattern.MatchString(head) {
+						UseColumns = append(UseColumns, i+1)
+					}
+
+				}
+			} else {
+				// we digress from go  best practises here, because if
+				// a colum spec is not a number, we process them above
+				// inside the err handler  for atoi(). so only add the
+				// number, if it's really just a number.
+				UseColumns = append(UseColumns, usenum)
+			}
+		}
+
+		// deduplicate
+		imap := make(map[int]int)
+		for _, i := range UseColumns {
+			imap[i] = 0
+		}
+		UseColumns = nil
+		for k := range imap {
+			UseColumns = append(UseColumns, k)
 		}
 	}
 	return nil
 }
 
+// prepare headers: add numbers to headers
 func numberizeHeaders(data *Tabdata) {
-	// prepare headers: add numbers to headers
 	numberedHeaders := []string{}
 	maxwidth := 0 // start from scratch, so we only look at displayed column widths
 
@@ -83,8 +117,8 @@ func numberizeHeaders(data *Tabdata) {
 	}
 }
 
+// exclude columns, if any
 func reduceColumns(data *Tabdata) {
-	// exclude columns, if any
 	if len(Columns) > 0 {
 		reducedEntries := [][]string{}
 		var reducedEntry []string

lib/helpers_test.go

@@ -45,6 +45,23 @@ func Testcontains(t *testing.T) {
 }
 
 func TestPrepareColumns(t *testing.T) {
+	data := Tabdata{
+		maxwidthHeader: 5,
+		maxwidthPerCol: []int{
+			5,
+			5,
+			8,
+		},
+		columns: 3,
+		headers: []string{
+			"ONE", "TWO", "THREE",
+		},
+		entries: [][]string{
+			{
+				"2", "3", "4",
+			},
+		},
+	}
 	var tests = []struct {
 		input     string
 		exp       []int
@@ -52,14 +69,15 @@ func TestPrepareColumns(t *testing.T) {
 	}{
 		{"1,2,3", []int{1, 2, 3}, false},
 		{"1,2,", []int{}, true},
-		{"a,b", []int{}, true},
+		{"T", []int{2, 3}, false},
+		{"T,2,3", []int{2, 3}, false},
 	}
 
 	for _, tt := range tests {
 		testname := fmt.Sprintf("PrepareColumns-%s-%t", tt.input, tt.wanterror)
 		t.Run(testname, func(t *testing.T) {
 			Columns = tt.input
-			err := PrepareColumns()
+			err := PrepareColumns(&data)
 			if err != nil {
 				if !tt.wanterror {
 					t.Errorf("got error: %v", err)

lib/io.go

@@ -44,6 +44,12 @@ func ProcessFiles(args []string) error {
 		if err != nil {
 			return err
 		}
+
+		err = PrepareColumns(&data)
+		if err != nil {
+			return err
+		}
+
 		printData(&data)
 	}