How to check if a Bash variable is True (false) with if statements in Bash programming language (scripting language) for Linux PCs and servers.
I don’t like implementing “options” in Bash functions. Those who have implemented options know, it requires about 60 lines, well, depending on the number. So when I really need option-like functionality within a function, what do I do? Yes, I use local variables.
hoge(){
# and more..
if ( [[ "${show_hr}" == true ]] || [[ "${show_hr}" == false ]] ) && "${show_hr}" ;
then
horizonal_line
fi
# and more..
}When executing a function like the above, if you pass a local variable show_hr, it will be used within the function. In this example, if you execute like show_hr=true hoge, the commands in the if block will be executed. If you want to pass false, use show_hr= hoge or show_hr=false hoge, and if you want to pass a value, use show_hr=value hoge.
The above if block lightly validates whether the type of show_hr is boolean. Without this validation, for example, if the value of show_hr is not a boolean value but foobar, you’ll get an error like not found command: foobar. So, well, if you don’t need validation, the following writing style is okay. After thinking it through, I recommend the above writing style as the best approach.
hoge(){
# and more..
if "${show_hr}" ;
then
horizonal_line
fi
# and more..
}I can see the benefits of type declaration languages like Java. You can make arrays plural by adding the suffix s, but there isn’t really a clear rule for boolean values. show_hr_boolean is too long. Maybe it’s not bad to do it like Ruby with show_hr?. Hmm.
Addition
By the way, when it’s true, even a string becomes true, but when it’s false, a string becomes true. When getting boolean values from JSON, you might get them as strings.
In such cases, it’s good to eval it.
{
"waked_up_once": "true"
}if eval "$( cat "${CONFIG_JSON}" | parsejson '["waked_up_once"]' )" ;
then
echo y
fi