Fix Windows colors: %ENV instead of exec prefix

Tested with GitHub for Windows 1.0.36.0 using cmd, Powershell, and Git
bash.
Coloration worked properly in all three environments. Git bash threw a
harmless "Unsuccessful stat on filename containing newline" warning, but
otherwise worked. (I blame the ancient perl included with msysgit.)

By adding a batch script launcher, we can thereby remove all the Windows
caveat documentation in the README file. To use eg, simply put this
directory
in your path, even on Windows.

Author: dfabulich

README

@@ -9,44 +9,6 @@ on each subcommand; for example, running
   eg help commit
 will explain how to commit and provide many examples of doing so.
 
-To Msysgit users [From Dan Fabulich]:
-  1) Msysgit users aren't supplied an ordinary git.exe executable on
-  the command-line, but a script called "git.cmd".  Out of the box,
-  "eg" can't find this script.
-
-  It's easy to update eg 0.99 to support a non-standard git executable
-  (for example: my $git_cmd = "git.cmd"), but that'll get you in
-  trouble...
-
-  2) ... because Perl's backtick (`) operator won't correctly detect
-  the return code of git in that case; it'll think that git.cmd always
-  returns 0.  This confuses eg's revision-detector code, etc.
-
-  The only workaround I've found is to make a copy of git.cmd and
-  change its behavior.  git.cmd terminates the script using "@exit /b
-  %ErrorLevel%"; I've made a copy called "gitx.cmd" that just uses
-  "@exit %ErrorLevel%" and I refer to "gitx.cmd" in eg; that works
-  perfectly.
-
-  3) eg assumes that you can set environment variables on the backtick
-  command-line like this: `GIT_PAGER_IN_USE=1 git log -1` ... that
-  works fine on UNIX but not on Windows.
-
-  I had to go through and comment out references to GIT_PAGER_IN_USE
-  to get "eg log" to work.  This disables color, but color is in a
-  wonky state on msysgit anyway, so I scarcely miss it.
-
-  I think there's another clever use of inline environment variables
-  in "eg revert"; it attempts to temporarily set GIT_INDEX_FILE when
-  reverting just unstaged changes.  I've never needed to do that, but
-  I'm sure I will someday :-p
-
-  I assume these inline variables are being used to make them
-  temporarily apply only to the child process?  Would it be harmful to
-  just set them as %ENV variables instead?
-(We should soon remove #3 from this README; I agree with Dan that we
-should just modify %ENV instead.)
-
 Note: bash-completion-eg.sh is NOT needed to run eg; it's here just for
 the people that have bash completion set up and want to use it with eg
 (google for bash_completion if you want to know more or how to make use of

eg

@@ -3300,8 +3300,12 @@ sub run {
   $names{$revision} = [$branch, 0];
 
   # Loop over the output of git log, printing/modifying as we go
-  my $use_colors = -t STDOUT ? "GIT_PAGER_IN_USE=1" : "";
-  open(INPUT, "$use_colors $git_cmd log @ARGV | ");
+  my $old_git_pager_in_use = $ENV{"GIT_PAGER_IN_USE"};
+  if (-t STDOUT) {
+    # use colors
+    $ENV{"GIT_PAGER_IN_USE"} = "1";
+  }
+  open(INPUT, "$git_cmd log @ARGV | ");
   $ENV{"LESS"} = "FRSX" unless defined $ENV{"LESS"};
   my $less = ($use_pager == 1) ? "less" :
              ($use_pager == 0) ? "cat" :
@@ -3330,6 +3334,7 @@ sub run {
   my ($ret1, $ret2, $ret3);
   close(INPUT);  $ret1 = $? >> 8;
   close(OUTPUT); $ret2 = $? >> 8;
+  $ENV{"GIT_PAGER_IN_USE"} = $old_git_pager_in_use;
 
   # Make sure we close the pipe from rev-list too; We use "$? && $!"
   # instead of "$?" because we don't care about the return value of the
@@ -5408,15 +5413,17 @@ sub run {
 
         if (@other_files || !$paths_specified) {
           my ($tmp_index) = Util::quote_args("$git_dir/tmp_index");
-          my $git_index = "GIT_INDEX_FILE=$tmp_index ";
 
           my $cf = "@other_files";
           if (!$paths_specified) {
             my ($cur_dir, $top_dir, $git_dir) = RepoUtil::get_dirs();
             ($cf) = Util::reroot_paths__from_to_files($top_dir, $cur_dir, '.');
           }
-          $ret = ExecUtil::execute("$git_index $git_cmd checkout $revision " .
+          my $old_git_index_file = $ENV{"GIT_INDEX_FILE"};
+          $ENV{"GIT_INDEX_FILE"} = $tmp_index;
+          $ret = ExecUtil::execute("$git_cmd checkout $revision " .
                                    "-- $cf", ignore_ret => 1);
+          $ENV{"GIT_INDEX_FILE"} = $old_git_index_file;
           exit $ret if $ret;
 
           $ret = ExecUtil::execute("rm $tmp_index");

eg.bat

@@ -0,0 +1,3 @@
+@echo off
+perl eg %*
+exit /b %errorlevel%