Getting a particular char

Getting a particular char

[DervishD]

    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

-- 
Linux Registered User 88736
http://www.pleyades.net & http://raul.pleyades.net/

Re: Getting a particular char

[DervishD]

    Hi all :)

 * DervishD <raul@pleyades.net> dixit:
>     If I want to get the character number 'n' from a parameter
[...]
>     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.

    Finally I did this way (thanks to Paul Eggert, coauthor of GNU
coreutils, for the help):

    expr "x$parameter" : ".\{n\}\(.\)"

    Where 'n' is the index of the character we want. Easy and fully
SUSv3 compliant, where {N} is a valid BRE for repetition.

    Raúl Núñez de Arenas Coronado

-- 
Linux Registered User 88736
http://www.pleyades.net & http://raul.pleyades.net/

RE: Getting a particular char

[Sean Johnston]

From: DervishD [mailto:raul@pleyades.net]
Sent: 06 August 2004 11:56

>     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.
> 

How about:

	parameter=`echo "$parameter" | cut -cn`

Sean.

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