Added: Write termux shell environment to /data/data/com.termux/files/usr/etc/termux/termux.env on app startup and package changes

The `termux.env` can be sourced by shells to set termux environment normally exported. This can be useful for users starting termux shells with `adb` `run-as` or `root`. The file will not contain `SHELL_CMD__` variables since those are shell command specific.

The items in the `termux.env` file have the format `export name="value"`.
The `"`\$` characters will be escaped with `a backslash `\`, like `\"` if characters are for literal value. Note that if `$` is escaped and if its part of variable, then variable expansion will not happen if `.env` file is sourced. The `\` at the end of a value line means line continuation. Value can contain newline characters.

The `termux.env` file should be sourceable by `POSIX` compliant shells like `bash`, `zsh`, `sh`, android's `mksh`, etc. Other shells with require manual parsing of the file to export variables.

Related discussion #2565

app/src/main/java/com/termux/app/TermuxApplication.java

@@ -12,6 +12,7 @@ import com.termux.shared.termux.crash.TermuxCrashUtils;
 import com.termux.shared.termux.file.TermuxFileUtils;
 import com.termux.shared.termux.settings.preferences.TermuxAppSharedPreferences;
 import com.termux.shared.termux.settings.properties.TermuxAppSharedProperties;
+import com.termux.shared.termux.shell.command.environment.TermuxShellEnvironment;
 import com.termux.shared.termux.shell.am.TermuxAmSocketServer;
 import com.termux.shared.termux.shell.TermuxShellManager;
 import com.termux.shared.termux.theme.TermuxThemeUtils;
@@ -48,9 +49,8 @@ public class TermuxApplication extends Application {
         // Check and create termux files directory. If failed to access it like in case of secondary
         // user or external sd card installation, then don't run files directory related code
         Error error = TermuxFileUtils.isTermuxFilesDirectoryAccessible(this, true, true);
-        if (error != null) {
-            Logger.logErrorExtended(LOG_TAG, "Termux files directory is not accessible\n" + error);
-        } else {
+        boolean isTermuxFilesDirectoryAccessible = error == null;
+        if (isTermuxFilesDirectoryAccessible) {
             Logger.logInfo(LOG_TAG, "Termux files directory is accessible");
 
             error = TermuxFileUtils.isAppsTermuxAppDirectoryAccessible(true, true);
@@ -59,10 +59,17 @@ public class TermuxApplication extends Application {
                 return;
             }
 
+            // Setup termux-am-socket server
             TermuxAmSocketServer.setupTermuxAmSocketServer(context);
+        } else {
+            Logger.logErrorExtended(LOG_TAG, "Termux files directory is not accessible\n" + error);
+        }
 
         // Init TermuxShellEnvironment constants and caches after everything has been setup including termux-am-socket server
         TermuxShellEnvironment.init(this);
+
+        if (isTermuxFilesDirectoryAccessible) {
+            TermuxShellEnvironment.writeEnvironmentToFile(this);
         }
     }
 

app/src/main/java/com/termux/app/TermuxService.java

@@ -19,6 +19,7 @@ import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 
 import com.termux.R;
+import com.termux.app.event.SystemEventReceiver;
 import com.termux.app.terminal.TermuxTerminalSessionClient;
 import com.termux.shared.termux.plugins.TermuxPluginUtils;
 import com.termux.shared.data.IntentUtils;
@@ -116,6 +117,8 @@ public final class TermuxService extends Service implements AppShell.AppShellCli
         mShellManager = TermuxShellManager.getShellManager();
 
         runStartForeground();
+
+        SystemEventReceiver.registerPackageUpdateEvents(this);
     }
 
     @SuppressLint("Wakelock")
@@ -172,6 +175,9 @@ public final class TermuxService extends Service implements AppShell.AppShellCli
             killAllTermuxExecutionCommands();
 
         TermuxShellManager.onAppExit(this);
+
+        SystemEventReceiver.unregisterPackageUpdateEvents(this);
+
         runStopForeground();
     }
 

app/src/main/java/com/termux/app/event/SystemEventReceiver.java

@@ -2,12 +2,18 @@ package com.termux.app.event;
 
 import android.content.BroadcastReceiver;
 import android.content.Context;
+import android.content.Intent;
+import android.content.IntentFilter;
+import android.net.Uri;
 
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 
 import com.termux.shared.data.IntentUtils;
 import com.termux.shared.logger.Logger;
+import com.termux.shared.termux.TermuxUtils;
+import com.termux.shared.termux.file.TermuxFileUtils;
+import com.termux.shared.termux.shell.command.environment.TermuxShellEnvironment;
 import com.termux.shared.termux.shell.TermuxShellManager;
 
 public class SystemEventReceiver extends BroadcastReceiver {
@@ -35,6 +41,11 @@ public class SystemEventReceiver extends BroadcastReceiver {
             case Intent.ACTION_BOOT_COMPLETED:
                 onActionBootCompleted(context, intent);
                 break;
+            case Intent.ACTION_PACKAGE_ADDED:
+            case Intent.ACTION_PACKAGE_REMOVED:
+            case Intent.ACTION_PACKAGE_REPLACED:
+                onActionPackageUpdated(context, intent);
+                break;
             default:
                 Logger.logError(LOG_TAG, "Invalid action \"" + action + "\" passed to " + LOG_TAG);
         }
@@ -44,4 +55,37 @@ public class SystemEventReceiver extends BroadcastReceiver {
         TermuxShellManager.onActionBootCompleted(context, intent);
     }
 
+    public synchronized void onActionPackageUpdated(@NonNull Context context, @NonNull Intent intent) {
+        Uri data = intent.getData();
+        if (data != null && TermuxUtils.isUriDataForTermuxPluginPackage(data)) {
+            Logger.logDebug(LOG_TAG, intent.getAction().replaceAll("^android.intent.action.", "") +
+                " event received for \"" + data.toString().replaceAll("^package:", "") + "\"");
+            if (TermuxFileUtils.isTermuxFilesDirectoryAccessible(context, false, false) == null)
+                TermuxShellEnvironment.writeEnvironmentToFile(context);
+        }
+    }
+
+
+
+    /**
+     * Register {@link SystemEventReceiver} to listen to {@link Intent#ACTION_PACKAGE_ADDED},
+     * {@link Intent#ACTION_PACKAGE_REMOVED} and {@link Intent#ACTION_PACKAGE_REPLACED} broadcasts.
+     * They must be registered dynamically and cannot be registered implicitly in
+     * the AndroidManifest.xml due to Android 8+ restrictions.
+     *
+     *  https://developer.android.com/guide/components/broadcast-exceptions
+     */
+    public synchronized static void registerPackageUpdateEvents(@NonNull Context context) {
+        IntentFilter intentFilter = new IntentFilter();
+        intentFilter.addAction(Intent.ACTION_PACKAGE_ADDED);
+        intentFilter.addAction(Intent.ACTION_PACKAGE_REMOVED);
+        intentFilter.addAction(Intent.ACTION_PACKAGE_REPLACED);
+        intentFilter.addDataScheme("package");
+        context.registerReceiver(getInstance(), intentFilter);
+    }
+
+    public synchronized static void unregisterPackageUpdateEvents(@NonNull Context context) {
+        context.unregisterReceiver(getInstance());
+    }
+
 }