Getting a particular char

[DervishD <raul@xxxxxxxxxxxx>]

    Hi all :)

    First of all, my excuses because although this is a shell related
question, is not exactly a zsh related question. Is more about
portability, about how to implement a zsh facility in portable shell.

    If I want to get the character number 'n' from a parameter, in
zsh I do something like: $parameter[n]. Easy, short... and non
portable.

    So I change it to something like 'expr substr $parameter n 1'.
This has some problems, like '$parameter' needing some tweaking so
'expr' doesn't whine because it starts with '(', '+', etc. or it is
something like the word 'match'. But all that is not important,
because the 'substr' expression is not SUSv3 compliant, so I cannot
do that neither.

    So I'm implementing it like that:

    # Dirty and ugly hack, needs some polishing...
    # First we get rid of all characters at the beginning
    while [ ${#parameter} -gt n ]
    do
        parameter=${parameter#?}
    done

    #   Now, get rid of the characters after
    # the one we are interested in

    while [ ${#parameter} -gt 1 ]
    do
        parameter=${parameter%?}
    done

    I would like another ideas, shorter, faster, or simply less ugly,
and it must be portable, so no zsh tricks :(( If you could please
help me... Thanks a lot in advance.

    Raúl Núñez de Arenas Coronado

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