Shell Programming and Scripting

His code is checking for any character(s) followed by a character that is not a number, followed by any character(s). I think you've missed seeing the bang (!) which implies not 0-9:

Code:

( *[!0-9]*|"" )

So it will issue an error if the string has any character that isn't an error, or is empty.

If you miss that, then yes it is confusing.

Code:

( [!0-9]|"" )

Y cant i just do this??

Code:

 ( [!0-9]|"" )

will just match a single character. If the user enters "a" it will print the error, but if the user enters "aa" it will not. So, by adding the two wildcard characters, you allow it to check for any number of characters, and to match if any of them isn't a digit. So it will reject all of these: "a" "aa" and "20a".

Thank!! shell really different from other programming language haha
If you dont mind can i ask you another double condition problem i having??

Code:

	while [ "$author" == "" -o "$title" == ""]; #User need to enter either author or title in order for search to begin
	do
	echo "Title : "
	read title
	echo "Author: "
	read author
	done

The logic confirm is correct i want the user to enter either 1 of the field, to check single field for empty string i can do it but that not what i want!! i went google research and saw ppl say must [[Type here]] i try also cannot, i try to play with the ""''`` also cannot =.=
Ya i also try with

Code:

while["$author" -eq ""] && ["$title" -eq ""]

Are you using bash or Kshell?

This should work regardless:

Code:

while [ "$author" = "" -a "$title" = ""];

You want to loop when both strings are empty (and) rather than one or the other. I'm not sure that the test command (single brackets) supports the double equal (==) which you had in your sample.

If you are using Kshell or bash I think this is a bit more efficient and easier to read:

Code:

while [[ "$author" == ""  ||  "$title" == "" ]]
do
.......code here......
done

Hope this makes sense.

Ok the 2nd 1 work thank man. Just to clear my doubt how do u know where to put the [] is there a standard way?? and also when do i use == instead of -eq.Lastly u will saying there are different shell is that right?? Different shell different writing style??

Glad that worked.

There are quite a few different shells. Most of them follow the same general syntax (based on the original Bourne shell sh) The most popular are Korn Shell (ksh) and bash. While their syntax may be very similar, they do operate differently in some cases. I prefer ksh as it allows for things that bash doesn't do.

Here is a link to an article on this site that might help answer some of your questions:
Linux.com :: Korn -- an extended shell


The single bracket expression (e.g. [...]) invokes the external test command. Execute [icode]man test[\icode] for more information. It isn't as efficient as using the builtin [[...]] evaluation expressions in ksh/bash, and requires the use of -xx operators for testing strings which I find difficult to read.

As to where to bracket, it depends on what I'm trying to do, but usually I try to have the entire expression inside a single pair of brackets (single or double).