Print E0 energy value from VASP calculations

e0.go

package main

import (
	"bufio"
	"fmt"
	"os"
	"path/filepath"
	"regexp"
)

func main() {
	args := os.Args[1:]

	// Check for help argument
	if len(args) > 0 && (args[0] == "-h" || args[0] == "--help") {
		printHelp()
		return
	}

	// If no directory is provided, use the current directory
	if len(args) == 0 {
		args = append(args, ".")
	}

	for _, dir := range args {
		e0, err := readEnergy(dir)
		if err != nil {
			fmt.Printf("%s is not a VASP calculation\n", dir)
		} else {
			fmt.Printf("%s: E0 = %f eV\n", dir, e0)
		}
	}
}

func printHelp() {
	fmt.Println("e0 - Read E0 values from OSZICAR files in given directories.")
	fmt.Println("Usage: e0 [DIRECTORY]...")
	fmt.Println("If no directory is given, the current working directory is used.")
}

func readEnergy(calcDir string) (float64, error) {
	filePath := filepath.Join(calcDir, "OSZICAR")
	file, err := os.Open(filePath)
	if err != nil {
		return 0, err
	}
	defer file.Close()

	var lastMatch string
	scanner := bufio.NewScanner(file)
	re := regexp.MustCompile(`E0\s*=\s*([-\d\.E\+]+)`)
	for scanner.Scan() {
		line := scanner.Text()
		if re.MatchString(line) {
			lastMatch = re.FindStringSubmatch(line)[1]
		}
	}

	if lastMatch == "" {
		return 0, fmt.Errorf("%s: E0 value not found", calcDir)
	}

	var e0 float64
	fmt.Sscanf(lastMatch, "%f", &e0)
	return e0, nil
}