A shell by any other name

In an earlier post, we discussed that a shell can be used for static content generation, due to its programmability. But why did I even start using tcsh as my shell in the first place? Isn’t bash the standard in the Linux world?

Most of us start using Linux with the default shell, which in most distributions is the ubiquitous bash.

I prefer a single-line prompt; I also prefer to have a relatively same-sized prompt rather than a prompt that jumps around wildly in length. Yet, I also want to know where I am in the directory tree before I run a command, without having to regularly run pwd as a sanity check.

This set of conflicting requirements presents a bit of a dilemma:

• I want to know where I am in the directory tree
• showing the full path in the prompt will bounce its length significantly
• showing just the last directory name is insufficient and confusing (or disastrous, depending on the command you might run)

As a middle-ground solution, we can print the last N elements of the directory tree, but it may still be a fair number of characters, and hence too long.

What if we could print that on the right side of the prompt, instead of the usual left?

The bash solution

Well, bash supports printing right-aligned text, e.g., see this example from ArchLinux:

rightprompt()
{
    printf "%*s" $COLUMNS "right prompt"
}

PS1='\[$(tput sc; rightprompt; tput rc)\]left prompt > '

which just gets us right-aligned text, but typing text next to it just makes it into a bit of a mess, as the shell doesn’t recognize the existence of the prompt and that it conflicts with your command, which leads to super confusing editing of the command you’re about to run.

Here’s what it looks like in bash as the length of your command-line grows:

left prompt >                                                                      right prompt
left prompt > if you keep typing a really,                                         right prompt
left prompt > if you keep typing a really, really,                                 right prompt
left prompt > if you keep typing a really, really, really long command,            right prompt
left prompt > if you keep typing a really, really, really long command, it overwritesght prompt

That said, if you overwrite even a part of the right-side prompt, and then delete it with Backspace, the right-side prompt entirely disappears (and doesn’t return), but it’s a bit of a kludge, and something you’ll always have to keep in mind.

The tcsh solution

On the other hand, this is a built-in feature of tcsh (no hacks or padding needed):

set prompt='%n@%m> '
set rprompt='%c5'

and you have a prompt that looks like the following:

user@hostname>                                                                       ~/git/repo

Now you have a fixed-width shape of the left-side prompt, and the right side will display up to 5 directories from your path (collapsing your home directory to simply ~ for compactness), and best of all: when your command length is long enough to overwrite the right-side prompt, tcsh automatically hides the right-side prompt entirely!

Here’s what it looks like in tcsh as the length of your command-line grows:

user@hostname>                                                                       ~/git/repo
user@hostname> if you keep typing a really,                                          ~/git/repo
user@hostname> if you keep typing a really, really,                                  ~/git/repo
user@hostname> if you keep typing a really, really, really long command,             ~/git/repo
user@hostname> if you keep typing a really, really, really long command, it disappears

That’s what it means to have first-class support for such features!

Note that this, of course, doesn’t at all stop you from using #!/bin/bash for your scripts for interoperability with others, but it’s a great usability improvement over bash.

However, using a shell that’s incompatible with bash syntax, and which is only popular with a minority of Linux users, you will note that many scripts, plugins, shell extensions, auto-completion scripts, etc. will no longer work for you out-of-the-box, so this trade-off may or may not be worthwhile for you.

All I can say is, caveat emptor.

Yet another shell?

In a future post, we’ll look into another shell that may be of interest, that supports not only right-hand prompts, but will bring together Vim and Emacs users in peace and harmony—stay tuned!

Addendum

The future post mentioned above is live!