Mailinglist Archive: opensuse (2496 mails)

["David C. Rankin" <drankinatty@xxxxxxxxxxxxxxxxxx>]

David Haller wrote:
> Hello,
>
> On Sun, 30 Nov 2008, David C. Rankin wrote:
> > alias wp='webpin $1'
>
> That does not work as you think.
>
> Aliases are substituted, not called with arguments.
>
> ==== man bash ====
> ALIASES
>        Aliases allow a string to be substituted for a  word  when
>        it  is  used  as  the first word of a simple command.
> ====
>
> >      But I wanted to have it give usage information if no argument was given
> > instead of just the default webpin "ERROR: you must specify the search 
> > criteria
> > as a parameter" if no search term was specified.
>
> You can't.
>
> >      The simple logic I wanted was and that works fine in a separate script 
> > is:
> >
> > if [[ $1 ]]; then
> >    webpin $1
> > else
> >    echo -e "\n\tusage: wp <filename>\n"
> >    exit 1
> > fi
>
> A script get's passed arguments.
>
> >      However, when I try and turn it into a 1-liner I get the expected 
> > results for
> > the echo statement, but I get the following error when webpin $1 is called:
> >
> > alias wp='if [[ $1 ]]; then webpin $1; else echo -e "\n\tusage: wp
> > <filename>\n"; fi'
>
> Note what happens if I add a ';' at the end:
>
> $ alias foo='if [[ $1 ]]; then webpin $1; else echo -e "\tusage: p 
> <filename>"; fi;'
>
> $ foo a b c
> $ foo a b c
> + [[ -n '' ]]
> + echo -e '\tusage: wp <filename>'
>         usage: wp <filename>
> + a b c
> bash: a: command not found
>
> Which is because foo a b c is substituted to:
>
>     if [[ $1 ]]; then ... fi; a b c
>
> (and "$1" expands to nothing).
>
> >      So my question is "what basic bash rule am I screwing up this time, 
> > and, how
> > do I fix it?" Thanks.
>
> See above. Use a function:
>
> wp() { if test -n "$1"; then webpin "$@"; else echo -e "..."; fi; }
>
> Passing "$@" instead of just "$1" to webpin makes it more flexible
> as you can pass options to wepin, e.g. "wp -d latest konqueror"


> HTH,
> -dnh

        Always David. That is a great explanation. Thanks.


-- 
David C. Rankin, J.D.,P.E.      |          openSoftware und SystemEntwicklung
Rankin Law Firm, PLLC           |             Countdown for openSuSE 11.1
www.rankinlawfirm.com           |        http://counter.opensuse.org/11.1/small
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