Add 'last' flag to print the last n lines of the log and implement ReadLastLines utility

Author: Timthreetwelve

cmd/printlog.go

@@ -55,4 +55,9 @@ func init() {
 	if err := viper.BindPFlag("totals", printlogCmd.Flags().Lookup("totals")); err != nil {
 		log.Printf("Error binding flag 'totals': %v", err)
 	}
+
+	printlogCmd.Flags().Int16P("last", "l", 0, "Prints only the last n lines of the log file.")
+	if err := viper.BindPFlag("last", printlogCmd.Flags().Lookup("last")); err != nil {
+		log.Printf("Error binding flag 'last': %v", err)
+	}
 }

utils/lastlines.go

@@ -0,0 +1,74 @@
+/*
+Copyright © 2025 Tim Kennedy
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+*/
+
+package utils
+
+import (
+	"io"
+	"os"
+)
+
+func ReadLastLines(filePath string, numLines int) ([]string, error) {
+	file, err := os.Open(filePath)
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+
+	stat, err := file.Stat()
+	if err != nil {
+		return nil, err
+	}
+
+	var lines []string
+	offset := stat.Size()
+	buffer := make([]byte, 1)
+	line := ""
+
+	for offset > 0 && len(lines) < numLines {
+		offset--
+		_, err := file.Seek(offset, io.SeekStart)
+		if err != nil {
+			return nil, err
+		}
+
+		_, err = file.Read(buffer)
+		if err != nil {
+			return nil, err
+		}
+
+		if buffer[0] == '\n' {
+			if line != "" {
+				lines = append([]string{line}, lines...)
+				line = ""
+			}
+		} else {
+			line = string(buffer[0]) + line
+		}
+	}
+
+	if line != "" && len(lines) < numLines {
+		lines = append([]string{line}, lines...)
+	}
+
+	return lines, nil
+}

utils/printlog.go

@@ -60,17 +60,31 @@ func PrintLog() error {
 	}
 	defer file.Close()
 
-	// Using bufio scanner here for memory-efficient line-by-line reading.
 	lineCounter := 0
 	scanner := bufio.NewScanner(file)
-	for scanner.Scan() {
-		fmt.Println(scanner.Text())
-		lineCounter++
+	getLast := viper.GetInt("last")
+
+	if getLast > 0 {
+		lastLines, _ := ReadLastLines(logFile, getLast)
+		for _, line := range lastLines {
+			fmt.Println(line)
+			lineCounter++
+		}
+	} else {
+		// Using bufio scanner here for memory-efficient line-by-line reading.
+		for scanner.Scan() {
+			fmt.Println(scanner.Text())
+			lineCounter++
+		}
 	}
 
 	// Print totals if flag is set
 	if viper.GetBool("totals") {
-		fmt.Printf("\n%s is %s and contains %d records.", logFile, formatFileSize(stat.Size()), lineCounter)
+		if lineCounter == 1 {
+			fmt.Printf("\n%s is %s.  %d record was printed.\n", logFile, formatFileSize(stat.Size()), lineCounter)
+		} else {
+			fmt.Printf("\n%s is %s.  %d records were printed.\n", logFile, formatFileSize(stat.Size()), lineCounter)
+		}
 	}
 
 	// Check for errors during scanning