From: "Chris F.A. Johnson" <cfajohnson@...>
Date: 2011-05-17T05:05:25+09:00
Subject: Re: Re (2): Linux utility with reverse index facility?

On 2011-05-16, no.top.post@gmail.com wrote:
> In article <r5g7a8-3a5.ln1@206-248-139-163.dsl.teksavvy.com>, "Chris F.A. Johnson" <cfajohnson@gmail.com> wrote: 
>
>> On 2011-05-16, no.top.post@gmail.com wrote:
>> > awk &stuff can "give me the the Nth element",
>> > but, without writing your own search-loop,
>> > what can "give me the index of the 'element'
>> > which is <elementValue>" ?
>> >
>> > I think it's called 'reverse indexing' ?
>> 
>>    Do you want 'grep -n'?
>> 
>>    If not, please be more specific.
>
> awk & grep are not typically used on arrays of single chars,
> but that's the simplest, to ilustrate the concept.
> Given the 6char array: [abcdef]

    That's not an array; it's a string (this is shell, not C).

><elementValue> means the value of the element.
> The first element has value "a".

   Why not use the correct term, 'character'? Then we would have
   understood what you meant.

> "the  index of the 'element' which is "e" is
><the 5th element>; which index is  4 or 5 depending
> on whether you count from 0 or 1 respectively.

index() {
    case $1 in
        *"$2"*) idx=${1%%$2*}
            echo "$(( ${#idx} + 1 ))" ;;
        *) echo 0 ;;
    esac
}

$ index abcdef c
3

-- 
   Chris F.A. Johnson, <http://cfajohnson.com>
   Author:
   Pro Bash Programming: Scripting the GNU/Linux Shell (2009, Apress)
   Shell Scripting Recipes: A Problem-Solution Approach (2005, Apress)