Question

We can redirect the error message to file named newfile using __________ command.

(a) cat  foo  errorfile

(b) cat  foo >errorfile

(c) cat errorfile>foo

(d) cat foo 2>errorfile

The question was posed to me by my school principal while I was bunking the class.

This interesting question is from Redirection and Pipes in division The Shell of Unix

Answer 1

Right answer is (d) cat foo 2>errorfile

The best explanation: Redirecting standard error requires the 2> symbol. Suppose if foo doesn’t exist then an error message ‘cannot open foo’ will be generated but we can send this message to another file. But here > and >> cannot be used. We have to use 2> symbol as the file descriptor number 2 represents the standard error stream.