Map shift-tab in vim to inverse tab in Vim - vim

Question

I've done some searching and found a wealth of information on binding keys in vim, but I can't find out, for sure, how to map shift-tab. Or what command I need to map it to for it to "tab backwards".
This is what I have at the moment:
map <S-tab> <S-,><S-,>
Possibly Relevant Information:
I'm running Debian with Terminal 2.22.3. with VIM - Vi IMproved 7.1

Answer 1

Vim already has built-in key commands for insert mode to shift the current line left or right one &shiftwidth. They are (in insert mode):
Ctrl-t : shift right (mnemonic "tab")
Ctrl-d : shift left (mnemonic "de-tab")
If you still want to use shift-tab, this is how you do it:
" for command mode
nnoremap <S-Tab> <<
" for insert mode
inoremap <S-Tab> <C-d>

Answer 2

Debugging why shift-tab in vim isn't performing an inverse tab in Vim
If you placed the code inoremap <S-Tab> <C-d> into your .vimrc and vim still isn't responding in insert mode, then that means your Shift-tab is being intercepted, gobbled, and ignored somewhere in the perilous 4-part journey between your keyboard and vim. You need to figure out where your Shift-Tab is getting silently orphaned.
Four stage journey of Shift+Tab between keyboard and vim
Keyboard -> Operating System
The first step of a keystroke's journey is the operating system that intercepts all keys and stops some of them to perform a behaviors for the Operating system. For example Alt+Tab which often means "change focus of current window to the next". If you send Alt+Tab into vim, vim will not respond because the operating system gobbled it. You have to find this keymapping area on your operating system. Windows, Mac and Linux are all different, and they have different programs that manage which keys are intercepted and which pass through to applications. Find this area and make sure your Shift+tab is set to pass-though to the Terminal you use.
Operating System -> Terminal Application
Step 2 assumes the OS allowed your Shift+Tab to pass through to your terminal Application that has focus. Your terminal application should have a configuration menu option (Most have more than one, that fight each other) under Settings -> shortcuts, or settings -> keymaps. There are hundreds of terminal apps out there and each have different ideologies for which keystrokes to trap and gobble and perform some action native to the app, or which to pass through to the shell. Find this area and make sure your Shift+tab is allowed to pass through and is passing through.
Terminal Application -> your Shell
Step 3 assumes your Terminal application allowed Shift+Tab to pass through to the shell. There is an area that defines which key combos are intercepted to perform an action on the shell, which pass through to the application that is on the front. For me this is inputrc but mac and Windows have different areas. You'll have to find this file and clear out anything that may be gobbling your Shift+Tab and erase that, or add a rule that says pass through.
Shell -> vim
Now we're at the level of Vim where the .vimrc can hear, trap and or rebroadcast the Shift+Tab to the next step in the command chain, and do whatever you want while it does so. Vim has the map keyword that controls this.
There's even a 5th step in the journey if we're talking about Browsers or webpages, who have interpreter engines that allow client side code to remap keys. But that's for a different post.
Debug chain instructions to isolate where your Shift+Tab is orphaned:
Make sure your OS isn't gobbling your Shift+tab and performing no-action. Try a different application like Eclipse, Browser or Notepad, and see if Shift+Tab performs any action. If it does then The OS is likely passing through your Shift+tab unaffected to applications.
Make sure your terminal app can receive and is receiving the Shift+Tab. Verify this by going to settings -> Shortcuts and erase any keymap that has Shift, or Tab in the name, then make a new keymapping that intercepts Shift+tab and performs some simple action like new tab doesn't matter. Save it, put focus in the terminal and press it, if a new tab appears then Terminal can hear and respond.
Make sure your terminal is passing through Shift+Tab to shell. Erase anything smelling of Tab or Shift in Settings -> keymaps and Settings -> Shortcuts. The default action (should be) do nothing and pass through.
Open any other shell program like nano, ed, or emacs. If any of these perform any action when you press Shift+Tab, then it's likely that the terminal is passing through Shift+tab to vim.
At this point we know vi/vim is receiving Shift+Tab, but not responding to it. To isolate the problem, blow away all your vim config files like .vimrc, .profile and anything under .vim. The problem could even be with vim or under /etc You run vanilla vim using vim -u NONE and make sure you're running vim. Vim's default behavior is straight pass through. So if Shift+Tab isn't doing something, then vi is bugged.
Uninstall vim with a blank config files/directories and re-install. If this doesn't work, then your operating system is bugged. Reinstall the operating system. If this doesn't work, throw the computer in the trash.

Answer 3

To test if vim actually gets your shift+tab go into insert mode
ctrl+v then tab and it should create a tab character
ctrl+v then shift+tab and it should create an inverse tab character (which appears as ^[[Z)
If it does not, then vim is not receiving the shift+tab input
In my case it was my terminal.
In the terminal window -> settings -> shortcuts
search shift+tab and unmap

Answer 4

OP's question specifies map, which applies to normal, visual, select, and operator-pending modes (see :h mapmode-nvo). I'm not sure such a mapping makes any sense in operator-pending mode, but it's very useful in visual and select modes. I'll also add forward indentation for completeness:
" both visual and select modes at once. gv means reselect the last selection
vnoremap <Tab> >gv
vnoremap <S-Tab> <gv
" just visual mode. this is unsurprisingly the same as vnoremap
xnoremap <Tab> >gv
xnoremap <S-Tab> <gv
" just select mode. <C-o> leaves select mode for visual mode, where the
" command is performed, and <C-g> reenters select mode from visual mode
snoremap <Tab> <C-o>>gv<C-g>
snoremap <S-Tab> <C-o><gv<C-g>
Please do note that Tab and CTRL-i map to each other in most terminal emulators, so mapping Tab can have unexpected results. See this question for more.

Answer 5

The following can be used with Vim tabs:
map <TAB> <ESC>gt<CR>
map <S-TAB> <ESC>gT<CR>