Here is the script I use under bash, which also eliminates non-existent directories from the path. I don't remember if it handles leading, trailing, or double colons directly.

strippath()
{
local ifs="$IFS"
IFS=:

local path
path=(${1:-${PATH}})

local p=${#path[*]}
until ((0 == p))
do
((--p))
if [ -d ${path[$p]} ]
then
local e;
for ((e = 0; e != p; ++e))
do
if [ "${path[$p]}" == "${path[$e]}" ]
then
unset path[$p]
break;
fi
done
else
unset path[$p]
fi
done

echo "${path[*]}"
IFS="$ifs"
}

PATH="$(strippath)"

Posted by Nevin ":-)" on September 06, 2007 at 05:48 PM BST #

[Trackback] I just read this blog entry about reducing your path and realised there were two reasons I would not be doing that: Calling perl from a dot file would be one step to far. I have some korn shell functions for manipulating PATH variabl...

Posted by The dot in ... --- ... on September 07, 2007 at 09:27 AM BST #

Below is a ksh version of the stuff above which converts the value of a PATH, FPATH or MANPATH variable to an array which is then manipulated (filter, remove, append etc.) and finally written back into a *PATH-like format (the advantage is that this is faster for larger number of elements (e.g. FPATH may contain a few dozend elements if various packages need to be combined)):
-- snip --
typeset -a x # needs ksh93q or higher
integer i
integer numelements

# fill array from a path-like variable (PATH, FPATH, MANPATH)
function pathtopatharray
{
typeset p="$1"
nameref ar=$2
ar+=( ${p//:/$'\n'} )
}

# convert path array back to path-like variable representation
function patharraytopath
{
nameref ar=$1
(IFS=':' ; print "${ar[*]}")
}

# print a path array with label and index
function printpatharray
{
nameref ar=$1
typeset label="$2"
integer numelements=${#ar}
integer i

for((i=0 ; i < numelements ; i++ )) ; do
printf "%s: element %d =\"%s\"\n" "${label}" i "${ar[i]}"
done
}

# filter path array via shell pattern
function filterpatharraybypattern
{
nameref ar=$1
typeset pattern="$2"
integer numelements=${#ar}
integer i

for((i=0 ; i < numelements ; i++ )) ; do
if [[ "${ar[i]}" = ${pattern} ]] ; then
printf "unsetting element %d =\"%s\"\n" i "${ar[i]}"
unset "ar[$i]"
fi
done
}

function appendtopatharrayifnotpresent
{
nameref ar=$1
typeset -A set_paths # paths which are set
integer numelements=${#ar}
integer i
typeset p

# use the assiciative array "set_paths" to remeber
# which paths are set - we use the path name as
# index to use it for lookup below
for((i=0 ; i < numelements ; i++ )) ; do
set_paths["${ar[i]}"]="${ar[i]}"
done

shift

while (( $# > 0 )) ; do
p="$1"

if [[ "${set_paths["$p"]}" = "" ]] ; then
set_paths["$p"]="$p"
ar+=( "$p" )
fi
shift
done

}

# main
pathtopatharray "${PATH}" x

# print array content
printpatharray x "loop 1"

# remove elements by fiter
# (extended regular expression to filter "games" and "mit" kerb stuff)
filterpatharraybypattern x '~(E)(mit|game)'

appendtopatharrayifnotpresent x "/bin" "/bin" "/bix" "/bax" "/bix"

# print new view of array
printpatharray x "loop 2"

# print new PATH variable
print "PATH=$(patharraytopath x)"

# EOF.
-- snip --

Output looks like this:
-- snip --
$ ksh x.sh
loop 1: element 0 ="/usr/local/bin"
loop 1: element 1 ="/usr/bin"
loop 1: element 2 ="/usr/X11R6/bin"
loop 1: element 3 ="/bin"
loop 1: element 4 ="/usr/games"
loop 1: element 5 ="/opt/gnome/bin"
loop 1: element 6 ="/opt/kde3/bin"
loop 1: element 7 ="/usr/lib/mit/bin"
loop 1: element 8 ="/usr/lib/mit/sbin"
loop 1: element 9 =""
loop 1: element 10 =""
loop 1: element 11 =""
loop 1: element 12 =""
loop 1: element 13 =""
unsetting element 4 ="/usr/games"
unsetting element 7 ="/usr/lib/mit/bin"
unsetting element 8 ="/usr/lib/mit/sbin"
loop 2: element 0 ="/usr/local/bin"
loop 2: element 1 ="/usr/bin"
loop 2: element 2 ="/usr/X11R6/bin"
loop 2: element 3 ="/bin"
loop 2: element 4 =""
loop 2: element 5 ="/opt/gnome/bin"
loop 2: element 6 ="/opt/kde3/bin"
loop 2: element 7 ="/bix"
loop 2: element 8 ="/bax"
loop 2: element 9 =""
loop 2: element 10 =""
loop 2: element 11 =""
loop 2: element 12 =""
loop 2: element 13 =""
PATH=/usr/local/bin:/usr/bin:/usr/X11R6/bin:/bin:/opt/gnome/bin:/opt/kde3/bin:/bix:/bax
-- snip --

Version with "insert_before", "insert_after" and more filter operations on demand.

Posted by Roland Mainz on September 07, 2007 at 11:51 PM BST #