[contrib] fish-like directory in prompt

[derf@sievert.tabularazor.org]

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Hi there,
I recently stumbled upon the "friendly interactive shell" (fish).

While I don't really like it, I was quite amazed by the way it displayes
the current directory in the prompt.
Basically, it only displays the tail of the path as full directory, and
truncates every directory name before it to its first character.
Example: /usr/share/zsh/functions/Completion -> /u/s/z/f/Completion

Apparently this feature was not available in zsh, so I wrote the
attached function for it.

As an addition to fish-like behaviour, it can also produce "tab-safe"
paths, so if you take the path, paste it into a shell and press tab,
it will safely expand to your current working directory.
The function can be configured both via commandline arguments and
zstyle.

Personally, I put its output into a psvar and use it in the prompt
instead of the current directory, but with the prompt_expansion option it
could also be used directly in the prompt.

Comments and suggestions are welcome.

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## vim:ft=zsh
## reverse tabbing, useful in the prompt
## Copyright (C) 2008 by Daniel Friesel <derf@derf.homelinux.org>
## License: WTFPL <http://sam.zoy.org/wtfpl>

## CAVEAT: directory-names containing two or more consecutive spaces
## are not yet supported

setopt localoptions
setopt rc_quotes null_glob

typeset -i lastfull=0
typeset -i short=0
typeset -i tilde=0
typeset -i named=0

if zstyle -t ':prompt:rtab' fish; then
	lastfull=1
	short=1
	tilde=1
fi
if zstyle -t ':prompt:rtab' nameddirs; then
	tilde=1
	named=1
fi
zstyle -t ':prompt:rtab' last && lastfull=1
zstyle -t ':prompt:rtab' short && short=1
zstyle -t ':prompt:rtab' tilde && tilde=1

while [[ $1 == -* ]]; do
	case $1 in
		-f|--fish)
			lastfull=1
			short=1
			tilde=1
		;;
		-h|--help)
			print 'Usage: rtab [-f -l -s -t] [directory]'
			print ' -f, --fish      fish-simulation, like -l -s -t'
			print ' -l, --last      Print the last directory''s full name'
			print ' -s, --short     Truncate directory names to the first character'
			print ' -t, --tilde     Substitute ~ for the home directory'
			print ' -T, --nameddirs Substitute named directories as well'
			print 'The long options can also be set via zstyle, like'
			print '  zstyle :prompt:rtab fish yes'
			return 0
		;;
		-l|--last) lastfull=1 ;;
		-s|--short) short=1 ;;
		-t|--tilde) tilde=1 ;;
		-T|--nameddirs)
			tilde=1
			named=1
		;;
	esac
	shift
done

typeset -a tree expn
typeset result part dir=${1-$PWD}
typeset -i i

[[ -d $dir ]] || return 0

if (( named )) {
	for part in ${(k)nameddirs}; {
		[[ $dir == ${nameddirs[$part]}(/*|) ]] && dir=${dir/${nameddirs[$part]}/\~$part}
	}
}
(( tilde )) && dir=${dir/$HOME/\~}
tree=(${(s:/:)dir})
(
	unfunction chpwd 2> /dev/null
	if [[ $tree[1] == \~* ]] {
		cd ${~tree[1]}
		result=$tree[1]
		shift tree
	} else {
		cd /
	}
	for dir in $tree; {
		if (( lastfull && $#tree == 1 )) {
			result+="/$tree"
			break
		}
		expn=(a b)
		part=''
		i=0
		until [[ (( ${#expn} == 1 )) || $dir = $expn || $i -gt 99 ]]  do
			(( i++ ))
			part+=$dir[$i]
			expn=($(echo ${part}*(/)))
			(( short )) && break
		done
		result+="/$part"
		cd $dir
		shift tree
	}
	echo ${result:-/}
)