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Re: set -x and parameter expansion

From: Peggy Russell
Subject: Re: set -x and parameter expansion
Date: Mon, 14 Mar 2011 06:38:03 +0000 (UTC)
User-agent: Loom/3.14 (http://gmane.org/)

> The `r' is not a word expansion.  It's a word that's evaluated as an
> expression when the command is executed.  Arithmetic expansion is
> the $((...)) word expansion.

The command being [[ and the dollar-sign indicating the expansion.

This helps clarify the "set -x" difference below which show $r going through
parameter expansion done by the shell before the command [[ sees the expression.

command [[ that            
contains expr               set -x
---------------         --------------
[[ $? -eq r ]]          + [[ 0 -eq r ]]  * [[ used the contents of r which was 0
[[ $? -eq $r ]]         + [[ 0 -eq 0 ]]
[[ $? -eq ${r:=0} ]]    + [[ 0 -eq 0 ]]

For a user to see/trace r, they would either echo/printf, declare -p r,
or refer to it as $r (displayed by set -x).  

Can users see more trace info on what happens within [[ (i.e.; [['s value for 

Thank you.
Peggy Russell

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