Re: [Xen-devel] xl command autocompletion: domain names

[John Haxby <john.haxby@xxxxxxxxxx>]

On 06/11/13 17:13, Ian Jackson wrote:
>  bash_completion_sudo () {
>     if [ x"`whoami`" = xroot ]; then "$@"
>     else ${BASH_COMPLETION_SUDO-sudo} "$@"; fi
>  }
>  bash_completion_sudo xl list

It's amazing how old constructs make it into new shell scripts for all
the wrong reasons.

A long time ago, maybe around Unix Edition 7, maybe before, it was
common to see

  [ x$foo = x ]

to test for an empty "$foo".   Note the lack of quotes.   If $foo is
indeed empty then this expanded to [ x = x ] (obviously).  Without the
x's you would get [ = "" ] which is equally obviously a syntax error.

At some stage, decades ago, [ "$foo" = "" ] became possible and the old
syntax which had a naked $foo became obsolete.

For some reason there has been a resurgence in the belief that you need
the x's _and_ the quotes.  You don't.  Ideally you'd eschew the archaic
construct altogether.

If this particular case, however, you actually want something quite
different:

  if [ $(id -u) -eq 0 ] ...

:)

jch

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