~-2 is shorter than messing with the dirs command but it does not improve over $c2. It does not rescue the whole directory stack misfeature which has no reason for existing as built-in C code inside Bash, with dedicated expansion syntax. It interferes with existing syntax, too; according to POSIX, that refers to the home directory of a user named -2.
We can "export c1" and the others to make them visible to child processes. That makes it possible to launch a subshell in which the parent shell's directory log is readily available.
Things that can be very effectively and ergonomically achieved with a bit of scripting in the user's environment should never be built into the command interpreter. That just adds to the executable size, documentation, and maintenance.
Personally, I'd find the completion output from `~-<Tab>` a worthy improvement, although admittedly with zsh you can configure completion to display both name and value for `$c<Tab>` too I guess(can't recall if that is possible with bash).
User names should not begin with a hyphen¹, so it shouldn't interfere with home directory references.
The child process point is an interesting one, I feel like you could workaround it by using a chpwd hook to export $dirstack and set it at startup(or a precmd function and $DIRSTACK if using bash). Something like `export DIRSTACK=${(pj#:#)dirstack}` in the hook and `dirstack=(${(ps#:#)DIRSTACK})` in the startup file. I'll concede this point though, as while a fun thought experiment the end result would be ghastly ;)
I'm noticing that in Bash, when I complete on ~-1 without a trailing slash, nothing happens. When I use $c1 and hit tab, it adds the slash for me! So in that situation, $c1 saves a keystroke. Well, not a keystroke per se, but having to use a different character rather than repeated Tab.
Also, I can shorten these variables to one letter, like $p, $q, ...
Bash has an option so that tab completion will expand out the directory.
shopt -s direxpand
this is useful because variables like $c1 or syntax like ~-1 entered into the history is not useful for recall.
I know about M-x C-e to expand everything, but that is far too clumsy compared to just the tab completion doing it.
Here is something: the direxpand option is not working for ~-n/[Tab] completions. Only for variable names!
My description above wasn't great. I meant completion would be an improvement in the sense that under zsh `~-<Tab>` can show not only the possible completion options, but also the value they expand to. For example, mine is set to display in the manner of a colorful version of the text below:
$ cd ~-
0 -- ~
1 -- ~/Downloads
2 -- ~/Desktop
The handling of tilde expansion under bash is a readline option, so users would configure it in their inputrc. It is pretty useful in general, because then it is also available to tools like imv¹ beyond just bash. Unfortunately, as it is handled separately from word completion you'd need to change the completion function to make it match the mark-directories behaviour you like.
If I wanted the text expanded for history use I'd probably expand it before writing using a zshaddhistory hook, but I don't think there is an equivalent in bash so changing the line buffer probably is the best option.
We can "export c1" and the others to make them visible to child processes. That makes it possible to launch a subshell in which the parent shell's directory log is readily available.
Things that can be very effectively and ergonomically achieved with a bit of scripting in the user's environment should never be built into the command interpreter. That just adds to the executable size, documentation, and maintenance.