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Full Discussion: Using arrays in bash using strings to bash built-in true
Top Forums Shell Programming and Scripting Using arrays in bash using strings to bash built-in true Post 302615107 by Scrutinizer on Thursday 29th of March 2012 07:16:43 AM
Old 03-29-2012
While I agree with Corona688 that there are no booleans in shell, they can be emulated to some extent using the true and false built-ins if you put them in variables. This is something I found out myself at some point, and although I don't see this practice very often, I sometimes like to use it in my scripts, because I think it makes the code more mnemonic.
Code:
parameter_A_used=true parameter_B_used=false

if $parameter_A_used && $parameter_B_used; then
  echo "True"
else 
  echo "False"
fi

Code:
if $parameter_A_used && ! $parameter_B_used; then
  echo "True"
else
  echo "False"
fi

Code:
$ a=true b=false
$ if $parameter_A_used && $parameter_B_used; then   echo "True"; else    echo "False"; fi
False
$ if $parameter_A_used && ! $parameter_B_used; then   echo "True"; else    echo "False"; fi
True

What really happens here is that the shell built-ins inside these variables get executed and then produce a 1 or 0 return code.

You do need to be careful and disciplined that you only set these variables in your script itself and only to true or false for boolean purposes. Do not use variables that can contain user input or for example input from a file, because the content of these variables will get executed and there can be a security risk involved if you are careless with that.

Also, since true and false are built-ins, they can be overridden by shell functions, so you need to be aware of that also, like with any other utility of built-in that you use your script..

If you are not comfortable with this then use 0 and 1 values and test for that in [ ... ] statements.
Last edited by Scrutinizer; 03-29-2012 at 10:05 AM..
 

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