Java RegEx pattern

[m6s]

Let's suppose we have, this in an XML
<cs:CUSTOMER_ID><cs:CUSTOMER_ID/>

and a pattern to match : ":CUSTOMER_ID>([A-Za-z][A-Za-z0-9]*|)"

Really, I understand that between the second [] looks for alpharethmetic.
But I don't understand the first [] and after the OR operator '|'.
Has anyone any experience to decipher it?

Thank you in advance

[JosAH]

Let's suppose we have, this in an XML
<cs:CUSTOMER_ID><cs:CUSTOMER_ID/>

and a pattern to match : ":CUSTOMER_ID>([A-Za-z][A-Za-z0-9]*|)"

Really, I understand that between the second [] looks for alpharethmetic.
But I don't understand the first [] and after the OR operator '|'.
Has anyone any experience to decipher it?

Thank you in advance

This part: [A-Za-z][A-Za-z0-9]* reads: one letter [A-Za-z] followed by zero or more
letters or digits [A-Za-z0-9]*.

The vertical bar | at the end is a syntax error and shouldn't be there. The | operator
is a choice A|B meaning either A or B for whatever A or B.

kind regards,

Jos

[m6s]

This part: [A-Za-z][A-Za-z0-9]* reads: one letter [A-Za-z] followed by zero or more
letters or digits [A-Za-z0-9]*.

The vertical bar | at the end is a syntax error and shouldn't be there. The | operator
is a choice A|B meaning either A or B for whatever A or B.

kind regards,

Jos

Could n't just say then [A-Za-z0-9]? ? So the english questionmark to say one or more?
I bet the | is the or for nothing, so to say bring me one ore more, or nothing.. I think..

[Ganon11]

[a-zA-Z0-9]* is very different from [a-zA-Z][a-zA-Z0-9]*. This first will match 123cat, and the second will not. Both, however, will match cat123.

The first, [a-zA-Z0-9]*, looks for any sequence of digits and letters. They can be in any order and are under no constraints.

The second, [a-zA-Z][a-zA-Z0-9]*, MUST match a letter first, and only then will match any sequence of letters or digits. So it can't match something starting with a number, which the first regex can.

Some word starting with a letter, but made of of digits and letters...sound like anything to you?

[m6s]

[a-zA-Z0-9]* is very different from [a-zA-Z][a-zA-Z0-9]*. This first will match 123cat, and the second will not. Both, however, will match cat123.

The first, [a-zA-Z0-9]*, looks for any sequence of digits and letters. They can be in any order and are under no constraints.

The second, [a-zA-Z][a-zA-Z0-9]*, MUST match a letter first, and only then will match any sequence of letters or digits. So it can't match something starting with a number, which the first regex can.

Some word starting with a letter, but made of of digits and letters...sound like anything to you?

It seems rather clear now, perhaps, however if we need the first word after the '>' whether name or number this trick is too restrictive I think. We could have loosen it a bit.....
I tried to some regexp utility or grep itself, but couln't get what the writer wanted to say...
In any case thank you very much... It was very detailed description.