Checking legality of a string

[Martin Baxter]

Eric Chatonet wrote:
> Hi Graham,

> I think that there should be also a solution using matchText :-)

> Le 25 janv. 06 à 16:25, graham samuel a écrit :
> 
>> What's the most economical way of checking that a string contains  
>> only certain characters? I'm just trying to check if a string  
>> contains letters, digits and underscores, and nothing else. The  ways 
>> I've thought of doing it seem clunky. Basically I want to script

or try...

function isvalid mystring
   return not (matchtext(mystring,"[^a-zA-Z0-9_]+?"))
end isvalid

# there is a match if any character other than a-z A-Z 0-9 or _ is found
# in mystring
# using not inverts the result so that the function returns true
# if the string is valid.

Martin Baxter