feat: replace dependency on Bash with /bin/sh for cross-platform compatibility

This ensures cross-platform compatibility and accessibility for a wider range of users.

Resolves: #68.

Author: pepa65

README.md

@@ -95,4 +95,4 @@ sudo bat persist
 
 Linux kernel version later than 5.4-rc1 which is the [earliest version to expose the battery charging threshold variable](https://github.com/torvalds/linux/commit/7973353e92ee1e7ca3b2eb361a4b7cb66c92abee).
 
-To persist the threshold setting between restarts, the application relies on [systemd](https://systemd.io/), particularly a version later than 244, and [Bash](https://www.gnu.org/software/bash/) which are bundled with most Linux distributions. 
+To persist the threshold setting between restarts, the application relies on [systemd](https://systemd.io/) version 244 or later, which is bundled with most Linux distributions.

bat.service

@@ -5,7 +5,7 @@ StartLimitBurst=0
 
 [Service]
 Type=oneshot
-ExecStart={{.Shell}} -c 'echo {{.Threshold}} > /sys/class/power_supply/BAT?/charge_control_end_threshold'
+ExecStart={{.Shell}} -c 'echo {{.Threshold}} > {{.Path}}'
 Restart=on-failure
 RemainAfterExit=true
 

main_linux.go

@@ -11,6 +11,7 @@ import (
 	"log"
 	"os"
 	"os/exec"
+	"path"
 	"path/filepath"
 	"strconv"
 	"strings"
@@ -143,15 +144,17 @@ func main() {
 			log.Fatal(err)
 		}
 
-		shell, err := exec.LookPath("bash")
+		shell, err := exec.LookPath("sh")
 		if err != nil {
 			if errors.Is(err, exec.ErrNotFound) {
-				fmt.Fprintln(os.Stderr, "Could not find Bash on your system.")
+				fmt.Fprintln(os.Stderr, "Could not find 'sh' on your system.")
 				os.Exit(1)
 			}
 			log.Fatal(err)
 		}
 
+		path := path.Join(first, threshold)
+
 		for _, event := range events {
 			tmpl, err := template.New("unit").Parse(unit)
 			if err != nil {
@@ -171,9 +174,10 @@ func main() {
 
 			service := struct {
 				Event     string
+				Path      string
 				Shell     string
 				Threshold int
-			}{event, shell, current}
+			}{event, path, shell, current}
 			if err := tmpl.Execute(f, service); err != nil {
 				log.Fatal(err)
 			}