bash, toggel variable value?

[zero2xiii]

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:

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:

echo $var
0
echo $var
1
echo $var
0
echo $var
1

[matt_symes]

Hi

Something along the lines of...

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 ?

selection="a";
var=0;

[ "$selection" = "a" ] && { [ "$var" = "0" ] && var="1" || var="0"; } 

echo "$var"

Kind regards

[zero2xiii]

Hay,

The second option works the way I intend it:

~/:~$ [ "$selection" = "a" ] && var="1" || var="0";
~/:~$ 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

[alan9800]

you might also try the following code

var=0
selection="a"

if [ "$selection" = "a" ]; then let "var=-(var=~var)"; fi

echo $var

[zero2xiii]

Hay,

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

~/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

[alan9800]

Hay,

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

~/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:

var=0
selection="a"

if [ "$selection" = "a" ]; then let "var=1^var"; fi

echo $var

let "var=1^var"
echo $var

[markbl]

To toggle var:

var=$((var==0))

[alan9800]

To toggle var:

var=$((var==0))

or also

var=$((1-var))

which avoids confusion between boolean values and arithmetic ones.