Merge pull request git-for-windows#434: Integrate git update-microsoft-git with apt-get

Extend the `git update-microsoft-git` builtin to call `apt-get` in a similar way we do `brew` on macOS.

Author: derrickstolee

README.md

@@ -101,14 +101,15 @@ git version
 scalar version
 ```
 
-To upgrade microsoft/git, you can run the necessary `brew` commands:
+To upgrade `microsoft/git`, you can run the necessary `brew` commands:
 
 ```shell
 brew update
 brew upgrade --cask microsoft-git
 ```
 
-Or you can run the `git update-microsoft-git` command, which will run those brew commands for you.
+Or you can run the `git update-microsoft-git` command, which will run those
+`brew` commands for you.
 
 ## Linux
 
@@ -125,6 +126,16 @@ sudo apt-get update
 sudo apt-get install microsoft-git
 ```
 
+To upgrade `microsoft/git`, you can run the necessary `apt-get` commands:
+
+```shell
+sudo apt-get update
+sudo apt-get upgrade microsoft-git
+```
+
+Or you can run the `git update-microsoft-git` command, which will run those
+`apt-get` commands for you.
+
 ### Ubuntu 21.04 (Hirsute)
 
 ```shell
@@ -134,6 +145,16 @@ sudo apt-get update
 sudo apt-get install microsoft-git
 ```
 
+To upgrade `microsoft/git`, you can run the necessary `apt-get` commands:
+
+```shell
+sudo apt-get update
+sudo apt-get upgrade microsoft-git
+```
+
+Or you can run the `git update-microsoft-git` command, which will run those
+`apt-get` commands for you.
+
 ### Other Ubuntu/Debian distributions
 
 Please use the most recent
@@ -152,7 +173,11 @@ which should have the same output:
 git version
 scalar version
 ```
+
+To upgrade, you will need to repeat these steps to reinstall.
+
 ### Non-Ubuntu/Debian distributions
+
 You will need to compile and install `microsoft/git` from source:
 
 ```shell

builtin/update-microsoft-git.c

@@ -56,8 +56,26 @@ static int platform_specific_upgrade(void)
 #else
 static int platform_specific_upgrade(void)
 {
-	error(_("update-microsoft-git is not supported on this platform"));
-	return 1;
+	int res;
+	struct strvec args = STRVEC_INIT;
+
+	printf("Updating apt-get with 'sudo apt-get update'\n\n");
+
+	strvec_pushl(&args, "sudo", "apt-get", "update", NULL);
+	res = run_command_v_opt(args.v, 0);
+	strvec_clear(&args);
+
+	if (res) {
+		error(_("'sudo apt-get update' failed; is apt-get installed?"));
+		return 1;
+	}
+
+	printf("\nUpgrading microsoft-git with 'sudo apt-get upgrade microsoft-git'\n\n");
+	strvec_pushl(&args, "sudo", "apt-get", "upgrade", "microsoft-git", NULL);
+	res = run_command_v_opt(args.v, 0);
+	strvec_clear(&args);
+
+	return res;
 }
 #endif