Re: Order of variable substitution (any SUS guru out there?)

[Dan Nelson <dnelson@xxxxxxxxxxxxxxx>]

In the last episode (Jul 28), Borzenkov Andrey said:
> Several times I happily removed files by doing
> 
> find . -name ... | (cd /master/rep; cpio -pmv $PWD)
> 
> the problem is apparently $PWD is evaluated only after  cwd is
> changed so cpio tries to copy files over themselves and removes them.
> 
> Reading SUS gives impression it is wrong. All substitutions are done
> (conceptually) in one pass before any command executes.

Are you referring to 
http://www.opengroup.org/onlinepubs/007904975/utilities/xcu_chap02.html#tag_02_09_01
?  That section talks about "simple commands".  You've got a pipeline
and a compound command, composed of three simple commands, each of
which gets its variables expanded at different times.

Under your interpretation, "(a=1 ; echo $a)" would not work, since "$a"
would be evaluated beofre "a=1" was executed.  :)

> Shell here also behaves the same:
> 
> $ find . -type f | (cd ../foo-m; cpio -pmv $PWD)
> /home/bor/tmp/foo/id_dsa
> /home/bor/tmp/foo/id_dsa.pub
> /home/bor/tmp/foo/id_rsa
> /home/bor/tmp/foo/id_rsa.pub
> 11 blocks

"Shell" being what?  
 
> while zsh gives
> 
> bor@itsrm2% find . -type f | (cd ../foo-m; cpio -pmv $PWD)
> cpio: Attempt to pass a file to itself.
> cpio: Attempt to pass a file to itself.
> cpio: Attempt to pass a file to itself.
> cpio: Attempt to pass a file to itself.
> 0 blocks
> 4 error(s)

Ash and bash do the same as zsh.  Try storing your original PWD in
another variable first:

pwd=$PWD ; find . -type f | (cd ../foo-m; cpio -pmv $pwd)
 
-- 
	Dan Nelson
	dnelson@xxxxxxxxxxxxxxx