shell_posix.go

//go:build !darwin && !plan9 && unix

package shell

import (
	"bufio"
	"os"
	"os/exec"
	"os/user"
	"strings"
)

// CurrentUserShell returns the current user's shell.
func CurrentUserShell() (string, bool) {
	// If the SHELL environment variable is set, use it.
	if shell, ok := os.LookupEnv("SHELL"); ok {
		return shell, true
	}

	// Try to get the current user. If we can't then fallback to the default
	// shell.
	u, err := user.Current()
	if err != nil {
		return DefaultShell(), false
	}

	// If getpwnam_r is available, use it.
	if shell, ok := cgoGetUserShell(u.Username); ok {
		return shell, true
	}

	// If getent is available, use it.
	if getent, err := exec.LookPath("getent"); err == nil {
		if output, err := exec.Command(getent, "passwd", u.Username).Output(); err == nil {
			if fields := strings.SplitN(strings.TrimSuffix(string(output), "\n"), ":", 7); len(
				fields,
			) == 7 {
				return fields[6], true
			}
		}
	}

	// If the user has an entry in /etc/passwd, use it.
	if f, err := os.Open("/etc/passwd"); err == nil {
		defer f.Close()

		s := bufio.NewScanner(f)
		for s.Scan() {
			fields := strings.SplitN(strings.TrimSuffix(s.Text(), "\n"), ":", 7)
			if len(fields) == 7 && fields[0] == u.Username {
				return fields[6], true
			}
		}

		_ = s.Err() // Ignore errors.
	}

	// Fallback to the default shell.
	return DefaultShell(), false
}