On 09/04/2012 05:13 AM, Roman Rakus wrote:
> Hi,
> Petr, adding to cc: list, found behaviour not documented, neither in man
> page nor bash ref manual:
> ${par-word} will do expansion of par, and if the par is unset it is
> substituted by word. It is different from ${par:-word}, where word is
> used when par is unset or null.
>
> Is it undocumented and deprecated, like $[]? Or just undocumented?
It is fully documented, and required by POSIX. Read two lines above:
When not performing substring expansion, using the forms
documented
below, bash tests for a parameter that is unset or null.
Omitting the
colon results in a test only for a parameter that is unset.
${parameter:-word}
Use Default Values. If parameter is unset or null, the
expanâ
sion of word is substituted. Otherwise, the value of
parameter
is substituted.
It's a shame that the form ${parameter-word} is not called out more
directly in a form easy to search for, and that you have to read in two
places to piece things together yourself; but it IS supported and
documented.
--
Eric Blake ebl...@redhat.com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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