Usage:
okpaths ENVAR [DELIM(:) [ITYPE{bcdpfls}(d) [PERMS{rwx}(x) [DEDUP{FL*}(F)]]]]
The [] notation here indicates optionality and defaults are in ().
This program echos re-assembled value for $ENVAR delimited by ASCII character
DELIM. Each retained element is i-node type ITYPE with permissions PERMS.
& optional de-duplication.
Eg., PATH=okpaths PATH keeps only existing (d)irs executable(x) by an invoking
user. DEPDUP starting with 'F' means keep F)irst use, while 'L' keeps L)ast use
& other means no de-dup (this is case-insensitive). So, eval okpaths PATH is
nice in rc/init scripts for Unix shells.
Blocks of the 5 params can repeat (since fork&exec add to shell init time).
The i-node type abbreviation is the somewhat standard (ls -l | find):
- b (B)lock device
- c (C)haracter device
- d (D)irectory
- p named (P)ipe/FIFO
- f Regular (F)ile
- l Symbolic (L)ink
- s Unix domain (S)ocket
eval $(okpaths PATH : d rx u) is useful in shell start-up scripts (like
~/.profile) where you might assemble a search path or man path or et cetera
from a variety of possible locations, but then want to trim the value down to
locations valid at shell init.
This trimming makes echo $ENVAR less noisy and may prevent annoying extra,
unneeded work during start-up of dependent programs. Sometimes this extra work
can be quite a lot, (e.g. with a slow NFS automounter), although just running
okpaths will have to do it at least once.
Note that login shells can be very long-lived and FS availability dynamic. So,
validity at okpaths/shell start-up-time is not a perfect solution.