Setting Integer Variables in Bash

[Tim McDaniel]

On Thu, 29 Jan 2009, Mark J. Reed wrote:
> On Thu, Jan 29, 2009 at 5:54 PM, whitewall wrote:
>> #! /cygdrive/c/cygwin/bin/bash
>> declare -i Red
>> declare -i Green
>> Red=10
>> Green=$Red+1
>
> Since you've declared both Green and Red as integer, you should just
> do Green=Red+1, without the dollar sign. Doing Green=$Red+1 first
> takes Red's value, which is stored as an integer, expands it back
> into its decimal string representation, and then reparses it to
> yield its integer value.

There IS one subtle difference.  If you're running with "set -x",
     Green=$Red+1
will echo
     + Green=10+1
But
     Green=Red+1
will echo
     + Green=Red+1
(assuming that you've not changed PS4, IFS, &c &c).  You can decide
which "set -x" output you like.  I found that I preferred the
substituted forms, the ones with $this and $that.

-- 
Tim McDaniel, tmcd@panix.com

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