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Thread: bash, toggel variable value?

  1. #1
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    bash, toggel variable value?

    Hay all,

    Somehow I can not get an answer from google for this. I wan to do a simple if, then, to toggle the value of a variable between 1 and 0:

    example:
    Code:
    var="0"
    selection="a"
    
    if [ $selection = "a" ]; then toggle $var; fi
    
    echo $var
    The result should be "1".

    I want to use this in a little interactive script for selecting and deselecting certain options. All the variables values are either zero or one.

    Thanks in advance

    EDIT:
    Just be clear I want $var to toggle between 1 and 0:
    Code:
    echo $var
    0
    echo $var
    1
    echo $var
    0
    echo $var
    1
    Last edited by zero2xiii; May 6th, 2013 at 03:01 PM.
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  2. #2
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    Re: bash, toggel variable value?

    Hi

    Something along the lines of...
    Code:
    selection="a";
    var=;
    
    [ "$selection" = "a" ] && var="1" || var="0";
    
    echo $var;
    Is that the kind of thing you want ?

    Or is it more like this ?

    Code:
    selection="a";
    var=0;
    
    [ "$selection" = "a" ] && { [ "$var" = "0" ] && var="1" || var="0"; } 
    
    echo "$var"
    Kind regards
    Last edited by matt_symes; May 6th, 2013 at 02:30 PM. Reason: Reread the original post
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  3. #3
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    Re: bash, toggel variable value?

    Hay,

    The second option works the way I intend it:

    Code:
    ~/:~$ [ "$selection" = "a" ] && var="1" || var="0";
    ~/:~$ echo $var
    1
    ~/:~$ [ "$selection" = "a" ] && { [ $var = "0" ] && var="1" || var="0"; }
    ~/:~$ echo $var
    0
    ~/:~$ [ "$selection" = "a" ] && { [ $var = "0" ] && var="1" || var="0"; }
    ~/:~$ echo $var
    1
    ~/:~$ [ "$selection" = "a" ] && { [ $var = "0" ] && var="1" || var="0"; }
    ~/:~$ echo $var
    0
    I will try this in the script and see if it works there .

    Thanks for the quick response!

    EDIT: It works in the script and I will credit you for the help . The script will be posted in my signature's link "help us help you" thread when I am done.
    Thanks
    Last edited by zero2xiii; May 6th, 2013 at 03:02 PM.
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  4. #4
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    Re: bash, toggel variable value?

    you might also try the following code
    Code:
    var=0
    selection="a"
    
    if [ "$selection" = "a" ]; then let "var=-(var=~var)"; fi
    
    echo $var

  5. #5
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    Re: bash, toggel variable value?

    Hay,

    That does not do what I want, it simply counts up:

    Code:
    ~/Scripts/DebugTool/:~$ var=0
    ~/Scripts/DebugTool/:~$ selection="a"
    ~/Scripts/DebugTool/:~$ if [ "$selection" = "a" ]; then let "var=-(var=~var)"; fi
    ~/Scripts/DebugTool/:~$ echo $var
    1
    ~/Scripts/DebugTool/:~$ if [ "$selection" = "a" ]; then let "var=-(var=~var)"; fi
    ~/Scripts/DebugTool/:~$ echo $var
    2
    ~/Scripts/DebugTool/:~$ if [ "$selection" = "a" ]; then let "var=-(var=~var)"; fi
    ~/Scripts/DebugTool/:~$ echo $var
    3
    ~/Scripts/DebugTool/:~$ if [ "$selection" = "a" ]; then let "var=-(var=~var)"; fi
    ~/Scripts/DebugTool/:~$ echo $var
    4
    ~/Scripts/DebugTool/:~$ 
    ]
    The above post's is a fix so thanks. It also works perfectly in the script so I will use that. Thanks
    Last edited by matt_symes; May 6th, 2013 at 03:01 PM. Reason: Fixed code tags :)
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  6. #6
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    Re: bash, toggel variable value?

    Quote Originally Posted by zero2xiii View Post
    Hay,

    That does not do what I want, it simply counts up:

    Code:
    ~/Scripts/DebugTool/:~$ var=0
    ~/Scripts/DebugTool/:~$ selection="a"
    ~/Scripts/DebugTool/:~$ if [ "$selection" = "a" ]; then let "var=-(var=~var)"; fi
    ~/Scripts/DebugTool/:~$ echo $var
    1
    ~/Scripts/DebugTool/:~$ if [ "$selection" = "a" ]; then let "var=-(var=~var)"; fi
    ~/Scripts/DebugTool/:~$ echo $var
    2
    ~/Scripts/DebugTool/:~$ if [ "$selection" = "a" ]; then let "var=-(var=~var)"; fi
    ~/Scripts/DebugTool/:~$ echo $var
    3
    ~/Scripts/DebugTool/:~$ if [ "$selection" = "a" ]; then let "var=-(var=~var)"; fi
    ~/Scripts/DebugTool/:~$ echo $var
    4
    ~/Scripts/DebugTool/:~$ 
    ]
    The above post's is a fix so thanks. It also works perfectly in the script so I will use that. Thanks
    Sorry, in my previous post I wrongly used the "~" (bitwise not) operator instead of "^" (bitwise xor) .
    Hopefully the following code should do what you wish:
    Code:
    var=0
    selection="a"
    
    if [ "$selection" = "a" ]; then let "var=1^var"; fi
    
    echo $var
    
    let "var=1^var"
    echo $var
    Last edited by alan9800; May 6th, 2013 at 10:02 PM.

  7. #7
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    Re: bash, toggel variable value?

    To toggle var:
    Code:
    var=$((var==0))

  8. #8
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    Re: bash, toggel variable value?

    Quote Originally Posted by markbl View Post
    To toggle var:
    Code:
    var=$((var==0))
    or also
    Code:
    var=$((1-var))
    which avoids confusion between boolean values and arithmetic ones.

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