Convert absolute symbolic links (those whose target starts with /) to be relative (to their containing directory). Written for Linux, but will work anywhere that has `readlink -m` and `ln -T` (the GNU versions do).

shorten-symlinks

#!/bin/bash

dryrun=false
verbose=false
root=/

[[ "--help" = "$1"* && $1 = --h* || "$*" = -h ]] && { cat <<EndOfHelp ; exit 0 ; }
${0##*/} [-v|-q] [-n|-N] [-r /PATH] [PATH ...]
EndOfHelp

while [[ $1 = -?* ]]
do
    case $1 in
    (-[r]?*)    _p=$1 ; shift ; set -- "${_p:0:2}"  "${_p:2}" "$@" ; continue ;;
    (-[^-]?*)   _p=$1 ; shift ; set -- "${_p:0:2}" "-${_p:2}" "$@" ; continue ;;

    (-N) dryrun=false ;;
    (-n) dryrun=true ;;
    (-q) verbose=false ;;
    (-r) root=$2 ; shift ;;
    (-v) verbose=true ;;
    (*)  echo >&2 "Invalid option '$1'" ; exit 64 ;;
    esac
    shift
done

for l do

    # canonicalize path (without resolving symlinks)
    [[ $l = /* ]] || l=${PWD%/}/$l
    l=${l//\/\//\/}
    while [[ $l = */./* ]] ; do l=${l//\/.\//\/} ; done

    t=$(readlink $l) || continue  # must be a symlink

    # canonicalize path AND resolve symlinks
    u=$(readlink -m $l) || break  # something very broken

    [[ $l = ${root%/}/* ]] || continue # symlink out of balliwick
    [[ $u = ${root%/}/* ]] || continue # target out of balliwick

    # trim common prefix from both paths
    # (or the entire target if it is a prefix of the symlink)
    if [[ "$l" = "$u"/* ]]
    then
        v=${l#"$u"/} u=.
    else
        v=$l
        while [[ "$u" = */* && "${u%%/*}" = "${v%%/*}" ]]
        do u=${u#*/} v=${v#*/}
        done
    fi

    # make target relative to symlink
    w=${v//[^\/]/}
    u=${w//\//..\/}$u

    # do nothing if nothing to change
    [[ "$t" = "$u" ]] && continue 

    if $verbose || $dryrun
    then
        printf "LINK %-47s REPLACE %-47s WITH %s\n" "$l" "$t" "$u"
    fi

    #
    if $dryrun
    then
        echo "ln -sfTv '$u' '$l'"
        echo "chown -hc --ref='$l~' '$l'"
        echo "rm -fv '$l~'"
    else
        ln -sfTv --backup=simple "$u" "$l" &&
        chown -hc --ref="$l~" "$l"
        [[ "$l" -ef "$l~" ]] &&
        rm -fv "$l~"
    fi
done

wtf is it that long