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Re: unset, set variables, and arithmetic and other options

Cross-posted to 2 groups.

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>>>>> Beta What <lite.on.beta@gmail.com> writes:

	[Cross-posting to news:comp.unix.shell, for obvious reasons.]

 > Does the shell (bash and csh) treat set variable that are set to
 > empty string "" same as unset variables.  I believe csh requires
 > variable to be set.  For bash, are unset and "" the same in all
 > contexts?  If not can you point me to when they are not?

	Consider, e. g.:

$ (a=value ; printf %s\\n "${a:-default}" "${a-default}") 
value
value
$ (a=      ; printf %s\\n "${a:-default}" "${a-default}") 
default

$ (unset a ; printf %s\\n "${a:-default}" "${a-default}") 
default
default
$ 

 > How about unset variable in operations, like arithmetic or tests?
 > From some tests it seems like bash treats unset variables as =0.

-- 
FSF associate member #7257

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unset, set variables, and arithmetic and other options Beta What <lite.on.beta@gmail.com> - 2012-02-25 22:46 -0800
  Re: unset, set variables, and arithmetic and other options Ivan Shmakov <oneingray@gmail.com> - 2012-02-26 14:55 +0700
    Re: unset, set variables, and arithmetic and other options Beta What <lite.on.beta@gmail.com> - 2012-02-26 00:18 -0800
      Re: unset, set variables, and arithmetic and other options Janis Papanagnou <janis_papanagnou@hotmail.com> - 2012-02-26 10:59 +0100
        Re: unset, set variables, and arithmetic and other options Geoff Clare <geoff@clare.See-My-Signature.invalid> - 2012-02-27 13:14 +0000
          Re: unset, set variables, and arithmetic and other options Kaz Kylheku <kaz@kylheku.com> - 2012-02-27 13:42 +0000
  Re: unset, set variables, and arithmetic and other options John McCue <jmccue@jmclin0.hsd1.ma.comcast.net> - 2012-02-26 16:20 +0000

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