Is there a way to assign bool variable in bash?

Question

My requirement is as follows,

if cond1 is true; then
    if [[ val1 -lt val2 ]]; then
        call_x_func
        call_y_func
        call_z_func
    fi
else
    if [[ val1 != val2 ]]; then
        call_x_func
        call_y_func
        call_z_func
    fi
fi

From above you can see that if cond1 is true then use operator -lt or else use !=. contents inside the loop remains the same. To acheive this, I am trying to do below but not able to assign bool value to bash variable. What would be the best way of doing this ?

need_change=false
if cond1; then
    need_change=[[ val1 -lt val2 ]]
else
    need_change=[[ val1 != val2 ]] 
fi

if $need_change; then
    call_x_func
    call_y_func
    call_z_func
fi

Answer 1

I often use "true" and "false" since they are also commands that merely return success and failure respectively. Then you can do

cond1=false
if "$cond1"; then ...fi

here what you looking for :

need_change=false
cond1=true
if "$cond1"; then
    if [[ val1 -lt val2 ]]; then need_change="true"; else need_change="false"; fi
else
    if [[ val1 -ne val2 ]]; then need_change="true"; else need_change="false"; fi
fi

if "$need_change"; then
    .
    .
fi

Answer 2

Since bash does not have a bool data type, I suggest that you model the bool by interpreting the numeric value 0 as true, and any other value as false. By doing this, you can easily use the exit code of programs as a boolean. For instance:

need_change=1  # set to false
((val1 < val2)) # Test the values
need_change=$? # Set to true or false, according to the outcome of the test
  # or:
need_change=$((val1 < val2)) # Alternative way to achieve this result.