Very basic question

Question

I'm starting to play with Regular Expression and have a very basic question:

I tried the regular expression ^\d$ thinking it would only recognize expressions with numbers, and here is why

1) the ^ means the expression has to begin with whatever follows it, right? in this case a number
2) the $ means the expression has to end with whatever precede it, right? in this case a number.

if my assumptions were correct, it would not recognize a1 or aaaa4, but it does. Where am I wrong?

Here is the little program I'm using to check my expressions.

static

 

void Main(string[] args)

{

 

if (Regex.IsMatch(args[1], args[0]))

 

Console.WriteLine("Input matches regular expression");

 

else

 

Console.WriteLine("Input does not match entry");

}

Thanks in advance.

Answer 1

bmunoz, your expression matches strings composed of one digits. So it matches "0", "1", "2", "3", "4", "5", "6", "7", "8" and "9".

In order to match a number you must specify that a the digit can appear many times "^\d+$"

The expression should not match "a1". Can you tell us how you call the executable? (what arguments are you passing)

Answer 2

Hi VictorHurdagaci

Thanks for your help with this. You were definably on to something. When I called the app this way TestRegExpr ^\d$ a1, a1 was accepted.

I modified the app, to print the regular expression before evaluating it, it came back to "\d$", so it was removing the ^ and that is why a1 was been accepted.

So if I call the app TestRegExpr ^^\d$ a1, the expression keeps the ^ and a1 is not accepted.

Thanks for the help.