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From: guy%gorodish@Sun.COM (Guy Harris)
Newsgroups: comp.unix.questions
Subject: Re: Korn Shell
Message-ID: <15224@sun.uucp>
Date: Wed, 18-Mar-87 00:56:47 EST
Article-I.D.: sun.15224
Posted: Wed Mar 18 00:56:47 1987
Date-Received: Thu, 19-Mar-87 06:41:24 EST
References: <580@csun.UUCP> <5680@brl-smoke.ARPA> <2201@ptsfa.UUCP> <730@hoqax.UUCP>
Sender: news@sun.uucp
Reply-To: guy@sun.UUCP (Guy Harris)
Organization: Sun Microsystems, Mountain View
Lines: 26
Keywords: Korn shell ksh aliases parameters

>Why can't aliases and functions be exported like shell variables?

The UNIX environment mechanism doesn't know about aliases and
functions.  The low-level mechanism only knows about strings; the
user-mode code (in the shells, and in "getenv" and "putenv") knows
about strings of the form "<name>=<value>".  You'd have to come up
with some convention to distinguish exported variables and aliases
from exported variables.  You would not be able to have an equals
sign *anywhere* in the alias or function, because the "getenv" code
is very simple-minded and would see any string containing an equals
sign as a "<name>=<value>" item.

Also, since the environment is treated just like a second argument
list, it is subject to the same size limitations as argument lists.
This means, on most machines, no more than 5120 or 10240 or 20480
(depending on your flavor of UNIX) characters in your argument and
environment lists combined.  My .kshrc is 4190 bytes; even if half
of them are comments, this is still a significant fraction of 5120.
If you get *really* fancy, you can push this limit - and remember,
this is a limit on the total size of environment variables *and*
arguments, so the bigger your environment gets, the smaller the
maximum number of arguments you can pass to a program gets.

It also takes time to copy a big environment when doing an "exec" -
and this time is spent on *every* "exec", regardless of whether it'll
use the values in the environment or not.