Bash command to check if the variable name is valid

Question

#check if the name is valid
function myfunc()
{
    #check "${1}"
    #echo "valid/invalid"
}

#these should return valid
myfunc "my_number"
myfunc "my_number1"

#these should return ivalid 
myfunc "1my_number"
myfunc "1my _number"
myfunc "my number"
myfunc "my_number?"

and so on the variable name can have only letters , numbers (but not on the beginning),.. and like all the rules for java...

Is there any function that I can use ? I do not want to reinvent the wheel...

Underlayer

Why do you think there would be a built in function in bash to check against variable name rules for Java? Different languages have different restrictions on what is allowed in a variable name. You are going to need to determine the rules for your language and environment yourself, and implement it with something like the regex that @dogbane suggested. – Innocency

Answer 1

Match the variable name against a regex, like this:

myfunc() {
    if [[ "$1" =~ ^[a-z][a-zA-Z0-9_]*$ ]]
    then
        echo "$1: valid"
    else
        echo "$1: invalid"
    fi
}

Ascertain

^[a-z][a-zA-Z0-9_]*$ would mark variables starting with an uppercase character invalid. May I suggest ^[a-zA-Z][a-zA-Z0-9_]*$? – Verdin

I did that on purpose. Java convention is not to start variables with an uppercase, but it's up to the OP to decide. It wasn't in his test cases. – Ascertain

It's also legal to begin a varname with underscore, so ^[_[:alpha:]][_[:alnum:]]*$ If you want to match case-insensitively, you can shopt -s nocasematch – Roundabout

Answer 2

dogbane's answer is almost complete for the context of bash variables, but it has not been updated to reflect the final comment which contains a fully working validator. According to his comment on his answer, this is intended. This answer provides a function which evaluates to true for all valid names and can be used as a condition rather than returning a value that must then be compared to something. Plus, it can be used across multiple shells.

 
The function:

isValidVarName() {
    echo "$1" | grep -q '^[_[:alpha:]][_[:alpha:][:digit:]]*$'
}

 
Example usage in bash:

key=...
value=...

if isValidVarName "$key"; then
    eval "$key=\"$value\""
fi


# or it might simply look like this

isValidVarName "$key" && eval "$key=\"$value\""

Rutkowski

Why the " && return || return 1" part? The return code of grep seems correct to me. – Nighttime

@OlivierPirson, you make an excellent point. I have no idea why I did that. Updating my answer. – Rutkowski

May I ask if there are any particular reasons not using [:alnum:] instead of [:alpha:][:digit:]? For instant I suggest '[[:alpha:]_][[:alnum:]_]*$' which is more concise. – Nymphalid

Answer 3

Bash only:

isvalidvarname ()
{
    local varname;
    local regexp_varname='^[_[:alpha:]][_[:alpha:][:digit:]]*$';
    varname="$1";
    [[ "${varname}" =~ ${regexp_varname} ]]
}

Edacity

Answer 4

A combination of already proposed answers. For all shells, by using grep:

is_valid_name() {  # NAME
    printf '%s' "$1" | grep --quiet '^[_[:alpha:]][_[:alpha:][:digit:]]*$'
}

For shells that accept regexp, like Bash:

function is_valid_name {  # NAME
    [[ "$1" =~ ^[_[:alpha:]][_[:alpha:][:digit:]]*$ ]]
}

Both return 0 (true) if NAME is a valid variable name, else return 1 (false). They can be used like this:

NAME='...'
is_valid_name "$NAME" && ...
if is_valid_name "$NAME"; then
    ...
fi

Nighttime