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Groups > comp.os.linux.misc > #35741

Re: correct quoting for variables in bash scripts?

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Ralf Fassel <ralfixx@gmx.de> wrote:
> | The two [[ ]] square bracket form of the test command is explicitly a
> | shell built-in, so it can recognize empty strings without help.
> 
> Interesting, didn't know that difference:
> 
>    $ unset bar
>    $ [[ $bar = x ]] && echo yes
>    $ type [[
>    [[ is a shell keyword
>    
>    $ [ $bar = x ] && echo yes
>    bash: [: =: unary operator expected
>    $ type [
>    [ is a shell builtin
> 
> Most probably the error thrown with "[" is to ensure compatibility with
> /usr/bin/test?

The error thrown with "[" is because what "[" sees as its argv is "= x" 
because the shell has already converted $bar into "" before "[" is 
executed.

Its complaint is that it found an operator it did not expect (the "=") in 
the argv[0] slot.  The error message is mathematically accurate, but 
very confusing to most users not well versed in math operator language 
("=" being a "binary operator" not a "unary operator").

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correct quoting for variables in bash scripts? Barry Stir <scooter@mealteam6.mil> - 2022-10-17 19:28 +0800
  Re: correct quoting for variables in bash scripts? Aragorn <telcontar@duck.com> - 2022-10-17 14:10 +0200
  Re: correct quoting for variables in bash scripts? Ralf Fassel <ralfixx@gmx.de> - 2022-10-17 14:15 +0200
    Re: correct quoting for variables in bash scripts? Jerry Peters <jerry@example.invalid> - 2022-11-01 20:27 +0000
  Re: correct quoting for variables in bash scripts? "Carlos E. R." <robin_listas@es.invalid> - 2022-10-17 14:39 +0200
  Re: correct quoting for variables in bash scripts? Rich <rich@example.invalid> - 2022-10-17 14:02 +0000
  Re: correct quoting for variables in bash scripts? Henning Hucke <h_hucke+spam.news@newsmail.aeon.icebear.org> - 2022-10-17 13:54 +0000
  Re: correct quoting for variables in bash scripts? Eli the Bearded <*@eli.users.panix.com> - 2022-10-17 23:35 +0000
    Re: correct quoting for variables in bash scripts? Ralf Fassel <ralfixx@gmx.de> - 2022-10-18 11:31 +0200
      Re: correct quoting for variables in bash scripts? Rich <rich@example.invalid> - 2022-10-18 12:02 +0000
        Re: correct quoting for variables in bash scripts? Ralf Fassel <ralfixx@gmx.de> - 2022-10-18 15:01 +0200
          Re: correct quoting for variables in bash scripts? Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2022-10-18 14:17 +0000
            The difference between /bin/test and /bin/[ Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2022-10-18 14:58 +0000
              Re: The difference between /bin/test and /bin/[ Eli the Bearded <*@eli.users.panix.com> - 2022-10-21 04:41 +0000
            Re: correct quoting for variables in bash scripts? Ralf Fassel <ralfixx@gmx.de> - 2022-10-19 12:04 +0200

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