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Groups > comp.os.linux.misc > #35739

Re: correct quoting for variables in bash scripts?

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In comp.os.linux.misc, Barry Stir  <scooter@mealteam6.mil> wrote:
> I see various formats, such as
>    if [[ -L ${LINK1_DIR} ]]; then
> 
>    if [[ -L "$LINK1_DIR" ]]; then
> 
> rather than just $LINK1_DIR I presume this is insurance to ensure
> script works in every version of Red Hat, Debian, Arch whatever...  So
> which is the ideal extra character to put around the environment
> variable?

As others have mentioned, ${} is to force parsing when being next to
something could confuse the variable name. The "$" version is to
force an empty tring to exist in contexts where it might get lost.

In your example neither is needed. Firstly there's nothing adjoining to
confuse the variable name. Secondly, it is [[ not [.

The one [ ] square bracket form of the test command needs empty string
protection because variable expansion happens before thecommand is run. 

The two [[ ]] square bracket form of the test command is explicitly a
shell built-in, so it can recognize empty strings without help.

Elijah
------
${} also gets used for manipulations like "base=${path##*/}"

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Thread

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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