Partial support for csh and cmd.exe

Both csh and cmd.exe are painful to script and may never be completely
supported.  In both cases, you will be better suited by just overriding
the shell:

  set shell=/bin/sh

Use of cmd.exe currently requires you to set shellslash.

plugin/fugitive.vim

@@ -27,6 +27,8 @@ endfunction
 function! s:shellesc(arg) abort
   if a:arg =~ '^[A-Za-z0-9_/.-]\+$'
     return a:arg
+  elseif &shell =~# 'cmd' && a:arg !~# '"'
+    return '"'.a:arg.'"'
   else
     return shellescape(a:arg)
   endif
@@ -616,12 +618,21 @@ function! s:Commit(args) abort
   let errorfile = tempname()
   try
     execute cd.'`=s:repo().tree()`'
-    let command = 'GIT_EDITOR=false '.s:repo().git_command('commit').' '.a:args
+    let command = ''
-    if a:args =~# '\%(^\| \)--interactive\>'
+    if &shell =~# 'cmd'
+      let old_editor = $GIT_EDITOR
+      let $GIT_EDITOR = 'false'
+    elseif &shell !~# 'csh'
+      let command = 'GIT_EDITOR=false '
+    endif
+    let command .= s:repo().git_command('commit').' '.a:args
+    if &shell =~# 'csh'
+      silent execute '!setenv GIT_EDITOR false; ('.command.' > '.outfile.') >& '.errorfile
+    elseif a:args =~# '\%(^\| \)--interactive\>'
       execute '!'.command.' 2> '.errorfile
     else
       silent execute '!'.command.' > '.outfile.' 2> '.errorfile
-    end
+    endif
     if !v:shell_error
       if filereadable(outfile)
         for line in readfile(outfile)
@@ -656,6 +667,9 @@ function! s:Commit(args) abort
   catch /^fugitive:/
     return 'echoerr v:errmsg'
   finally
+    if exists('old_editor')
+      let $GIT_EDITOR = old_editor
+    endif
     call delete(outfile)
     call delete(errorfile)
     execute cd.'`=dir`'
@@ -1182,15 +1196,29 @@ endfunction
 " }}}1
 " File access {{{1
 
-function! s:ReplaceCmd(cmd) abort
+function! s:ReplaceCmd(cmd,...) abort
   let fn = bufname('')
   let tmp = tempname()
   let aw = &autowrite
+  let prefix = ''
   try
+    if a:0 && a:1 != ''
+      if &shell =~# 'cmd'
+        let old_index = $GIT_INDEX_FILE
+        let $GIT_INDEX_FILE = a:1
+      elseif &shell =~# 'csh'
+        let prefix = 'setenv GIT_INDEX_FILE '.s:shellesc(a:1).'; '
+      else
+        let prefix = 'GIT_INDEX_FILE='.s:shellesc(a:1).' '
+      endif
+    endif
     set noautowrite
-    silent exe '!'.escape(a:cmd,'%#') ' > '.tmp
+    silent exe '!'.escape(prefix.a:cmd,'%#').' > '.tmp
   finally
     let &autowrite = aw
+    if exists('old_index')
+      let $GIT_INDEX_FILE = 'old_index'
+    endif
   endtry
   silent exe 'keepalt file '.tmp
   silent edit!
@@ -1209,19 +1237,19 @@ function! s:BufReadIndex()
     let b:git_dir = s:repo().dir()
     setlocal noro ma
     if fnamemodify($GIT_INDEX_FILE !=# '' ? $GIT_INDEX_FILE : b:git_dir . '/index', ':p') ==# expand('%:p')
-      let indexspec = ''
+      let index = ''
     else
-      let indexspec = 'GIT_INDEX_FILE='.s:shellesc(expand('%')).' '
+      let index = expand('%')
     endif
     if b:fugitive_display_format
-      call s:ReplaceCmd(indexspec.s:repo().git_command('ls-files','--stage'))
+      call s:ReplaceCmd(s:repo().git_command('ls-files','--stage'),index)
       set ft=git nospell
     else
       let cd = exists('*haslocaldir') && haslocaldir() ? 'lcd ' : 'cd '
       let dir = getcwd()
       try
         execute cd.'`=s:repo().tree()`'
-        call s:ReplaceCmd(indexspec.s:repo().git_command('status'))
+        call s:ReplaceCmd(s:repo().git_command('status'),index)
       finally
         execute cd.'`=dir`'
       endtry