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From: "Bart Schaefer" <schaefer@candle.brasslantern.com>
Message-Id: <961001173420.ZM24672@candle.brasslantern.com>
Date: Tue, 1 Oct 1996 17:34:20 -0700
In-Reply-To: Huy Le <huyle@xeno.ugcs.caltech.edu>
        "zsh3.0.0 bug: aliases in if-statement" (Oct  1,  4:51pm)
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To: Huy Le <huyle@xeno.ugcs.caltech.edu>, zsh-workers@math.gatech.edu
Subject: Re: zsh3.0.0 bug: aliases in if-statement
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On Oct 1,  4:51pm, Huy Le wrote:
> Subject: zsh3.0.0 bug: aliases in if-statement
> 
> unalias a b 2>/dev/null
> alias a=cat
> if true; then
>   alias b=cat
>   works() { echo yes | a }
>   fails() { echo yes | b }
> fi
> works2() { echo yes | b }

I've been complaining about this for ages.  The problem is that zsh
parses and completely tokenizes the whole "if" statement before it
executes any of it.  Thus the textual replacement of "cat" for "b"
in the fails() function, can't happen, because "b" is already a token
rather than a string subject to alias expansion.

Your example is just a more subtle variant of:

fails2() { echo yes | foo }
alias foo=cat

The workaround, of course, is either:

if true; then
  alias b=cat
  works() { echo yes | a }
  eval 'worksToo() { echo yes | b }'
fi

or:

if true; then
  alias b=cat
  works() { echo yes | a }
  worksToo() { echo yes | eval b }
fi

IMHO, alias expansion has always happened too soon in zsh, but it greatly
complicates matters to go around reshaping syntax trees at execution time.