make it possible to update via git extras

Installation.md

@@ -34,13 +34,18 @@ and the basic [msys2][1].
 Second, clone the `git-extras` repo into any folder you like.
 ```bash
 git clone https://github.com/tj/git-extras.git
+# checkout the latest tag (optional)
+git checkout $(git describe --tags $(git rev-list --tags --max-count=1))
 ```
-After that, open the script `install.cmd` in the folder with any text editor you like.
-Modify the `PREFIX` variable to where your `Git for Windows 2.x` is installed.
+
+After that, execute the `install.cmd` in the command prompt, with the path your `Git for Windows 2.x` is installed.
 For example, I install it in the folder called `C:\SCM\PortableGit` and
 the `PREFIX` should be `C:\SCM\PortableGit\mingw64` (for 64-bit release)
-or `C:\SCM\PortableGit\mingw32` (for 32-bit release).
-Third, execute the `install.cmd` directly or in the command prompt.
+or `C:\SCM\PortableGit\mingw32` (for 32-bit release). So I will execute the `install.cmd` like this:
+```batch
+install.cmd "C:\SCM\PortableGit\mingw64"
+```
+
 Last, please copy `colrm.exe` and `column.exe` from `folder-your-msys2-installed/usr/bin` to
 `folder-your-git-installed/usr/bin`.
 Enjoy `git-extras`!

bin/git-extras

@@ -13,12 +13,40 @@ update() {
     && echo "... updated git-extras $VERSION -> $(git extras --version)"
 }
 
+updateForWindows() {
+  local bin=$(which git-extras)
+  local prefix=${bin%/*/*}
+  local orig=$PWD
+  
+  # we need to clean up /tmp manually on windows
+  cd /tmp \
+    && rm -rf ./git-extras \
+    && echo "Setting up 'git-exras'...." \
+    && git clone https://github.com/tj/git-extras.git &> /dev/null \
+    && cd git-extras \
+	&& git checkout \
+        $(git describe --tags $(git rev-list --tags --max-count=1)) \
+        &> /dev/null \
+	&& ./install.cmd "$prefix" \
+	&& cd "$orig" \
+	&& echo "... updated git-extras $VERSION -> $(git extras --version)"
+  rm -rf /tmp/git-extras &> /dev/null
+}
+
 case "$1" in
   -v|--version)
     echo $VERSION && exit 0
     ;;
   update)
-    update
+    platform=$(uname -s)
+    if [ $(expr substr "$platform" 1 9) = "CYGWIN_NT" ] || \
+      [ $(expr substr "$platform" 1 10) = "MINGW32_NT" ] || \
+      [ $(expr substr "$platform" 1 10) = "MINGW64_NT" ]
+    then
+      updateForWindows
+    else
+      update
+    fi
     ;;
   *)
     git extras --help

install.cmd

@@ -1,5 +1,6 @@
 @ECHO OFF
 SET PREFIX=C:\SCM\PortableGit\mingw64
+IF NOT "%~1"=="" SET PREFIX="%~1"
 SET HTMLDIR=%PREFIX%\share\doc\git-doc
 SET GITEXTRAS=%~dp0
 
@@ -22,6 +23,6 @@ FOR %%i in (%COMMANDS_WITHOUT_REPO%) DO (
 	MORE +2 %GITEXTRAS%\bin\%%i >> %PREFIX%\bin\%%i
 )
 
-ROBOCOPY %GITEXTRAS%\man %HTMLDIR% *.html
+ROBOCOPY /IS %GITEXTRAS%\man %HTMLDIR% *.html
 
 @ECHO ON