[Novalug] bash weirdness

[Jon LaBadie]

On Fri, Apr 09, 2010 at 03:57:23PM -0400, Chris Snyder wrote:
> Can somebody please explain to me what this bash snippet is doing?  Why is my
> array data disappearing outside of the 'while'?  Bash doesn't have scoping by
> default unless you use local or something like that.  WTF?!?
> 
> thx
> Gopher.
> 
> --------------------
> #!/bin/bash
> 
> ls | while read output; do
>          data[$i]="$output"
>          let i++
>          echo "Current array size: " ${#data[*]}
> done
> 
> echo "Final array size" ${#data[*]}
> 

As others have noted, bash runs control structures
redirected to or from pipes in a separate process.

Here are three other alternatives I've not seen mentioned.

1. Use ksh instead of bash.

2. Redirect from a subprocess

  #!/bin/bash

  while read output; do
         data[$i]="$output"
         let i++
         echo "Current array size: " ${#data[*]}
  done <  <(ls)

  echo "Final array size" ${#data[*]}

3. Redirect into a subprocess

  #!/bin/bash

  ls | {
  while read output; do
         data[$i]="$output"
         let i++
         echo "Current array size: " ${#data[*]}
  done <  <(ls)

  echo "Final array size" ${#data[*]}
  }

-- 
Jon H. LaBadie                  jon at jgcomp.com
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