fix: fix persistence issue on some distributions

This fixes an issue, #12, on some
distributions where the Bash shell is not located in /usr/bin/ by
falling back to the one in /bin/ or returning an error otherwise.

README.md

@@ -41,7 +41,7 @@ There have also been some [problems setting the charging threshold inside of a v
 
 ## Installation
 
-Precompiled binaries (Linux x86-64) are available from the [GitHub releases page](https://github.com/leveson/bat/releases), the latest of which can be downloaded from [here](https://github.com/leveson/bat/releases/download/0.8/bat).
+Precompiled binaries (Linux x86-64) are available from the [GitHub releases page](https://github.com/leveson/bat/releases), the latest of which can be downloaded from [here](https://github.com/leveson/bat/releases/download/0.8.1/bat).
 
 After downloading the binary, give it permission to execute on your system by running the following command. For example, assuming the binary is located in the user's Downloads folder:
 

cmd/bat/main.go

@@ -47,6 +47,9 @@ func main() {
         err := persist.WriteServices()
         if err != nil {
             switch {
+            case err.Error() == "bash not found":
+                fmt.Println("Requires Bash to persist the charging threshold.")
+                os.Exit(1)
             case err.Error() == "incompatible systemd version":
                 fmt.Println("Requires systemd version 244-rc1 or later.")
                 os.Exit(1)

internal/docs/version.txt

@@ -1,3 +1,3 @@
-bat 0.8
+bat 0.8.1
 Copyright (c) 2021 Tshaka Eric Lekholoane.
 MIT Licence.

internal/persist/persist.go

@@ -18,6 +18,28 @@ import (
 //go:embed unit.tmpl
 var unit string
 
+// bashLocation returns the location of the Bash shell as a string. A
+// successful call returns err == nil. It will return the first instance
+// found starting by searching in /usr/bin/ and then in /bin/ as a last
+// resort.
+func bashLocation() (string, error) {
+    _, err := os.Stat("/usr/bin/bash")
+    if err != nil {
+        if os.IsNotExist(err) {
+            _, err = os.Stat("/bin/bash")
+            if err != nil {
+                if os.IsNotExist(err) {
+                    return "", errors.New("bash not found") 
+                }
+                return "", err
+            }
+            return "/bin/bash", nil
+        }
+        return "", err
+    }
+    return "/usr/bin/bash", nil
+}
+
 // hasRequiredSystemd returns true if the systemd version of the system
 // in question is later than 244 and returns false otherwise. (systemd
 // v244-rc1 is the earliest version to allow restarts for oneshot
@@ -85,14 +107,18 @@ func WriteServices() error {
     if !ok {
         return errors.New("incompatible systemd version")
     }
+    shell, err := bashLocation()
+    if err != nil {
+        return err
+    }
     threshold, err := io.FileContents("charge_control_end_threshold")
     if err != nil {
         return err
     }
     units := [3]Service{
-        {"boot", "multi-user", threshold},
-        {"hibernation", "hibernate", threshold},
-        {"sleep", "suspend", threshold},
+        {"boot", shell, "multi-user", threshold},
+        {"hibernation", shell, "hibernate", threshold},
+        {"sleep", shell, "suspend", threshold},
     }
     tmpl, err := template.New("unit").Parse(unit)
     if err != nil {

internal/persist/service.go

@@ -3,6 +3,7 @@ package persist
 // Service holds information for a systemd service.
 type Service struct {
     Event     string
+    Shell     string
     Target    string
     Threshold string
 }

internal/persist/unit.tmpl

@@ -6,7 +6,7 @@ StartLimitBurst=0
 [Service]
 Type=oneshot
 Restart=on-failure
-ExecStart=/usr/bin/bash -c 'echo {{ .Threshold }} > /sys/class/power_supply/BAT?/charge_control_end_threshold'
+ExecStart={{ .Shell }} -c 'echo {{ .Threshold }} > /sys/class/power_supply/BAT?/charge_control_end_threshold'
 
 [Install]
 WantedBy={{ .Target }}.target