Question

Which of the following is an invalid variable?

(a) _user

(b) us01

(c) -txtfile

(d) txt123

The question was asked by my college professor while I was bunking the class.

My enquiry is from Command Substitution and Shell Variables topic in division The Shell of Unix

Answer 1

Correct option is (c) -txtfile

The explanation is: UNIX restricts some rule for defining a variable. A variable name must begin with either an underscore (_) or alphanumeric character followed by one or more alphanumeric or underscore characters.