Emacs offers convenient variables for customizing indentation styles: indent-tabs-mode and sws-tab-width. For many programming modes, a user can set these variables globally, and they will automatically be applied to different file formats. Of course, these can be customized per-mode with hooks.
However, shell-mode does not appear to respect these variables, only responding to its own internal variable names sh-basic-offset and sh-indentation. In the future, could shell-mode please automatically default these to follow sws-tab-width, so that fewer individual modes require specific configuration?