is-valid-identifier

Is valid identifier?

Given a string, determine if it's a valid identifier.

Here is the syntax for valid identifiers:

• Each identifier must have at least one character.
• The first character must be picked from: alpha, underscore, or dollar sign. The first character cannot be a digit.
• The rest of the characters (besides the first) can be from: alpha, digit, underscore, or dollar sign. In other words, it can be any valid identifier character.

Examples of valid identifiers:

• i
• wo_rd
• b2h

Examples of invalid identifiers:

• 1i
• wo rd
• !b2h