ProgrammingThis forum is for all programming questions.
The question does not have to be directly related to Linux and any language is fair game.
Notices
Welcome to LinuxQuestions.org, a friendly and active Linux Community.
You are currently viewing LQ as a guest. By joining our community you will have the ability to post topics, receive our newsletter, use the advanced search, subscribe to threads and access many other special features. Registration is quick, simple and absolutely free. Join our community today!
Note that registered members see fewer ads, and ContentLink is completely disabled once you log in.
If you have any problems with the registration process or your account login, please contact us. If you need to reset your password, click here.
Having a problem logging in? Please visit this page to clear all LQ-related cookies.
Get a virtual cloud desktop with the Linux distro that you want in less than five minutes with Shells! With over 10 pre-installed distros to choose from, the worry-free installation life is here! Whether you are a digital nomad or just looking for flexibility, Shells can put your Linux machine on the device that you want to use.
Exclusive for LQ members, get up to 45% off per month. Click here for more info.
i am using regcomp and regexec to find out whether a string is a valid host name
a valid host name (according) to wikipedia is anything that
-starts with a-z or A-Z
-followed by 0 or more of a-z, A-Z, 0-9 or '-'
-and ends with a-z, A-Z or 0-9
Even if "a-" WAS a valid host name (which I doubt), then your answer still misses my point: The core of my question was "why does the above regex match something like 'a-' and 'a?'"
1) ([a-zA-Z])..any ONE letter out of a-z or A-Z
2) (([a-zA-Z])([a-z0-9A-Z-])*([a-z0-9A-Z]))..any ONE letter out of a-z or A-Z followed by 0 or more out of [a-z0-9A-Z-] and ENDING WITH ANY ONE out of [a-z0-9A-Z]
my understanding is this CANNOT possibly match anything ending with "-", let alone "?" or any other special character...BUT IT DOES!!...WHY?
These do exactly the same thing:
([a-z-])
([-a-z])
Theoretically you are correct, but the first one ([a-z-]) can fail depending on program/version used and/or *nix flavor that is used (error being: A closing character is expected after z-).
If you want to make sure no error will occur use the second one ([-a-z]).
LinuxQuestions.org is looking for people interested in writing
Editorials, Articles, Reviews, and more. If you'd like to contribute
content, let us know.