Thread: checking command line argument count [ac],linux

Suppose the following two commands are acceptable

Code:

$copy hello.txt bye.txt
$copy -f hello.txt bye.txt

I would like to say this
If user does NOT enter 3 or 4 arguments return error

Code:

if (ac != 3 || ac !=4)
 display error

else {
  ...
}

When I do enter $copy hello.txt bye.txt or $copy -f hello.txt bye.txt , it sitll gives me error. This doesn't make sense, since I entered 3 OR 4 arguments

HOWEVER, when I change the if statements to
if (ac != 3 && ac !=4), the program goes onto the else statement

Originally Posted by bos1234

When I do enter $copy hello.txt bye.txt or $copy -f hello.txt bye.txt , it sitll gives me error. This doesn't make sense, since I entered 3 OR 4 arguments

If it's 3 then it's NOT 4, if it's 4 then it's NOT 3.

Try this?

Code:

if(argc < 3 || argc > 4)

Originally Posted by Subsonics

If it's 3 then it's NOT 4, if it's 4 then it's NOT 3.

Try this?

Code:

if(argc < 3 || argc > 4)

The above logic works.
Why doesn't my one work? Isn't it also correct?

Code:

if arguments are not equal to 3 or 4 
    display error

but I have supplied 3 agruments

thanks for the explanation but i sitll dont get it

I wrote
if arguments supplied is NOT 3 OR 4
display error

$cp hello.txt bye.txt

3 arguments supplied.
argc != 3 will have (false), since argument supplied IS 3
argc != 4 will have (true), since argument supplied IS NOT 4
proceed

Originally Posted by bos1234

if arguments supplied is NOT 3 OR 4
display error

$cp hello.txt bye.txt

3 arguments supplied.
argc != 3 will have (false), since argument supplied IS 3
argc != 4 will have (true), since argument supplied IS NOT 4
proceed

What you are saying is, if either of the tests fail, print an error message. Well, if argc is 3 then it's not 4 so that test will fail, and conversely if argc is 4 then it's not 3 so that test will fail.

thanks man, i got it now

Originally Posted by Subsonics

Code:

if arguments supplied is NOT 3 OR 4

this should actually be

Code:

if arguments supplied is NOT ( 3 OR 4 )

an this is the same as

Code:

if arguments supplied is ( NOT 3 ) AND ( NOT 4 )

Kurt

Originally Posted by QuantumPete

No, you posted:

Code:

if (ac != 3 || ac !=4)

And that in the middle is an OR, not an AND.

I'm confused, the quote is from bos1234 not me. What did I say where, can you make an actual quote?

Originally Posted by Subsonics

I'm confused, the quote is from bos1234 not me. What did I say where, can you make an actual quote?

@QuantumPete: I just was not sure if you agreed or not. My position is:

A | B | !A OR !B
--+---+-----------
1 | 1 | 0
0 | 1 | 1
1 | 0 | 1
0 | 0 | 1

That is, the test "if( argc != 3 or argc != 4 ) will only fail if argc is both 3 and 4 at the same time, the equivalent would be.

A | B | !(A AND B)
--+---+-----------
1 | 1 | 0
0 | 1 | 1
1 | 0 | 1
0 | 0 | 1