> #!/bin/sh
> if test "$#" == "0"; then
>    lineno="1"
> else
>    lineno=$1
> fi

> ip link | \
>    cut -d ' ' -f2 | \
>    grep ^w | \
>    sed -e "s/:\s*$//" | \
>    head -n $lineno | \
>    tail -n 1

     Doesn't work out of the box.

     If /usr/bin/test was invoqued you should write '-eq' instead of 
'=='. But shell languages have non-standard built-ins. If /bin/sh points 
to dash, like in Debian, then the built-in test would accept '='. I 
guess '==' is a bashism (actually the adoption of a Cism by a shell 
language). Replacing '==' by '=' just works.

     Thanks for the script nevertheless :-)

     Didier