Code challenge: Bash prompt path shortener

Question

I implemented a prompt path shortener for bash to be included in the PS1 environment variable, which shortens the working directory into something more compact but still descrip

Answer 1

This was my own solution when I had the idea for this challenge. The inspiration actually came from Jolexa's Blog.

So here it is, the ruby implementation in readable form:

a = ARGV[1].gsub(%r{^#{ENV['HOME']}}, "~")
b, a = a, a.gsub(%r{/(\.?[^/.])[^/]+(/.*)}, '/\1\2') while
  (a.length > ARGV[2].to_i) && (b != a)
print a

And the actual one-line implementation within the bash function:

_dir_chomp() {
  ruby -e'a="'$1'".gsub(%r{^'$HOME'},"~");b,a=a,a.gsub(%r{/(\.?[^/.])[^/]+(/.*)},"/\\1\\2")while(a.length>'$2')&&(b!=a);print a'
}

Answer 2

Pure Bash:

_dir_chomp () {
    local IFS=/ c=1 n d
    local p=(${1/#$HOME/\~}) r=${p[*]}
    local s=${#r}
    while ((s>$2&&c<${#p[*]}-1))
    do
        d=${p[c]}
        n=1;[[ $d = .* ]]&&n=2
        ((s-=${#d}-n))
        p[c++]=${d:0:n}
    done
    echo "${p[*]}"
}

For purposes of testing, I'm assuming that the question means that the current user is "user1".

Note: Bash 4 has a variable PROMPT_DIRTRIM that shortens the \w escape in PS1 by retaining the number of sub-directories according to its value and replacing the rest with ...

/$ PROMPT_DIRTRIM=2
/$ echo $PS1
\w\$
/$ pwd
/
/$ cd /usr/share/doc/bash
.../doc/bash$

Answer 3

This one is 20 or so characters shorter than my other answer:

_dir_chomp () {
    local p=${1/#$HOME/\~} b s
    s=${#p}
    while [[ $p != "${p//\/}" ]]&&(($s>$2))
    do
        p=${p#/}
        [[ $p =~ \.?. ]]
        b=$b/${BASH_REMATCH[0]}
        p=${p#*/}
        ((s=${#b}+${#p}))
    done
    echo ${b/\/~/\~}${b+/}$p
}

Answer 4

This is how I shorten my bash prompt w/ full path in titlebar (works since 3.0):

_PS1P=('' '..')
PROMPT_COMMAND='_PS1L=${#DIRSTACK[0]} _PS1D=${DIRSTACK[0]}'
PS1='\[\e]2;\h:\w\a\]\h ${_PS1P[$_PS1L>36]}${_PS1D:$_PS1L>36?-34:0} \$ '

This method requires very low CPU overhead.

Answer 5

Another solution with only bash internals, no use of sed

shortpath()                                                                                                                                                                                                                                                                   
{           
    dir=${1%/*} && last=${1##*/}                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                

    res=$(for i in ${dir//\// } ; do echo -n "${i:0:3}../" ; done)                                                                                                                                                                                                            
    echo "/$res$last"                                                                                                                                                                                                                                                         
} 

My previous solution, with bash and sed. it cut each dir in 3 first caracters and add '..' like this: /hom../obo../tmp../exa../bas../

shortpath()
{
        dir=$(dirname $1)
        last=$(basename $1)

        v=${dir//\// } # replace / by <space> in path
        t=$(printf "echo %s | sed -e 's/^\(...\).*$/\\\1../' ; " $v) 
            # prepare command line, cut names to 3 char and add '..'
        a=$(eval $t) 
            # a will contain list of 3 char words ended with '..' ans separated with ' '

        echo " "$a"/"$last | sed -e 's/ /\//g'
}