Re: Full path with ksh emulation

["Brian K. White" <brian@xxxxxxxxx>]

----- Original Message ----- 
From: "Peter Stephenson" <pws@xxxxxxx>
To: <zsh-users@xxxxxxxxxx>
Sent: Thursday, January 05, 2006 7:44 AM
Subject: Re: Full path with ksh emulation


> "Tony Hasler" <tony@xxxxxxxxxxxxxxxxxxxx> wrote:
> > Accordingly, they have hit upon the idea of using zsh to emulate ksh. 
> > That
> > certainly solves the original problem, but introduces a new one.  In ksh 
> > the
> > 'whence' command always gives you the absolute path of its argument.  So
> > 'whence $0' always gives a full path even if the command was executed by
> > typing './myscript'.  I can find no straightforward way to do this in 
> > zsh.

Why arent they just using the real ksh93? It's readily available precompiled 
for linux. You didn't say what distribution, but for example, on SuSE it's 
right there in yast easy as pie.
Drop it in there and you're done without messing with the scripts at all.

I did just get done saying how ksh93 is not a 100% drop-in for ksh88 that 
ships with Solaris and HP-UX,  but it's certainly closer than pdksh or zsh.

I have run into other subtle things with zsh's ksh that break things. 
Example:
In real ksh, TTY is set by the shell, but you may overwrite it, and if you 
export it, the value holds in the children.
In zsh's ksh, you may overwrite TTY but exporting it has no effect. It's 
reset by the shell in each new child. (a kind person on this list point
These scripts, and a lot of application code, were written under sh where 
there is no built-in $TTY.
Probably that particular thing will never bother you, but can you really 
imagine that there are no other such land mines?

And I would definitely not have that detect /usr/local/bin/zsh code added to 
the scripts. Just put the real ksh in path and wherever else the bang-lines 
expect it.

You will need to deal with differences in the various system commands 
though.
Some have a fallback mode where they recognize traditional options even 
though they are not the normally correct options, that may be good enough, 
like ps will do "ps -ef" and lp will do "lp -dprintername"
Some are simply naturally compatible enough because most of the differences 
are in the form of extensions & enhancements that don't break backwards 
compatibilty with older traditional versions.
Like sed and awk both have more commands and can accept very large 
(unlimited? binary data too?) input records, but that doesn't hurt you if 
your code already works under older ones.
So you might not have too much grief on that score.
But then there are even dumber things. I have a couple of much-used scripts 
that have to react to uname so that they can use different command line 
options for "sort" of all things :)

Sometimes I deal with this by putting say "gfind ...|gxargs ..." instead of 
"find ... xargs" in a script and seeing to it that gnu find & xargs is 
installed on every box, since it's available on all platforms.
and /usr/local/bin/gfoo on a SCO/Solaris/HP box doesn't harm anything that 
depends on "foo" being the stock foo, and it's trivial to make symlinks on 
linux/bsd boxes from gfoo to foo.
It's better than maintaining multiple versions of scripts that each only 
work on one platform, and better than trying to put a lot of brains into 
scripts so that they can do different things on different platforms.

That same theory also could be an argument for switching over to bash or zsh 
across the board instead of trying to use zsh on linux and ksh on HP/UX.
Rather than have /bin/ksh that might behave any of at least 4 ways (ksh88, 
ksh93, pdksh, zsh) write new scripts in zsh explicitly and see to it that 
zsh is installed everywhere.
I did that, and I hate to admit it on the zsh mail list but did it with 
ksh93 not zsh. my scripts have "#!/bin/ksh93" at the top.
It's simpler to put a binary or a symlink to an existing binary on each box 
than to hack up and then maintain all the scripts.


Brian K. White  --  brian@xxxxxxxxx  --  http://www.aljex.com/bkw/
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filePro  BBx    Linux  SCO  FreeBSD    #callahans  Satriani  Filk!



> Put the following function after the "emulate ksh".  It doesn't
> cover all possibilities but it should do the basics.  (It's annoying
> there's apparently no way of rationalising the path to a directory without
> changing into it.)
>
> whence () {
>  # Version of whence which expands the full path to an
>  # executable.  Uses the builtin whence if the argument
>  * is not found in the path.
>  # N.B.: doesn't test if the argument matches an alias, builtin
>  # or function first, unlike the builtin.
>  local p f
>  # Ensure pushd doesn't ignore duplicates,
>  # and doesn't output messages
>  emulate -L zsh
>  setopt pushdsilent
>
>  if [[ $1 != /* ]]; then
>    for p in $path; do
>      if [[ -x $p/$1 ]]; then
>        f=$p/$1
> # Temporarilly switch to the directory of the file found.
> # This rationalises the directory path.
>        pushd $f:h
>        print $PWD/$f:t
>        popd
>        return
>      fi
>    done
>  fi
>  builtin whence $1
> }
>
> --
> Peter Stephenson <pws@xxxxxxx>                  Software Engineer
> CSR PLC, Churchill House, Cambridge Business Park, Cowley Road
> Cambridge, CB4 0WZ, UK                          Tel: +44 (0)1223 692070
>
>
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