various changes:

- added copying in every file
- disasembled rootCmd into separate wrapper func
- print usage if no file and no stdin

cmd/processinput.go

@@ -0,0 +1,79 @@
+/*
+Copyright © 2022 Thomas von Dein
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program. If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package cmd
+
+import (
+	"errors"
+	"github.com/alecthomas/repr"
+	"os"
+	"strconv"
+	"strings"
+)
+
+func process(args []string) error {
+	var pattern string
+	havefiles := false
+
+	if len(Columns) > 0 {
+		for _, use := range strings.Split(Columns, ",") {
+			usenum, err := strconv.Atoi(use)
+			if err != nil {
+				die(err)
+			}
+			UseColumns = append(UseColumns, usenum)
+		}
+	}
+
+	if len(args) > 0 {
+		if _, err := os.Stat(args[0]); err != nil {
+			pattern = args[0]
+			args = args[1:]
+		}
+
+		if len(args) > 0 {
+			for _, file := range args {
+				fd, err := os.OpenFile(file, os.O_RDONLY, 0755)
+				if err != nil {
+					die(err)
+				}
+
+				data := parseFile(fd, pattern)
+				if Debug {
+					repr.Print(data)
+				}
+				printTable(data)
+			}
+			havefiles = true
+		}
+	}
+
+	if !havefiles {
+		stat, _ := os.Stdin.Stat()
+		if (stat.Mode() & os.ModeCharDevice) == 0 {
+			data := parseFile(os.Stdin, pattern)
+			if Debug {
+				repr.Print(data)
+			}
+			printTable(data)
+		} else {
+			return errors.New("No file specified and nothing to read on stdin!")
+		}
+	}
+
+	return nil
+}