Exact pattern match?

oakley has asked for the wisdom of the Perl Monks concerning the following question:

Im trying to match either the word "yes" or the word "no" in its exact form... so far, no luck...

How in the world do I go about doing this? The current regex I have is allowing things like "yessir" and "nope" when I want to force it to only be either yes or no...

Here is the snippet:

 while ( ($addques{$key}{answer} eq "") || ($addques{$key}{answer} !~ 
+/$addques{$key}{format}/) )
 {
  print " Invalid answer/option - try again\n";
  print "$addques{$key}{question}";
  chomp($addques{$key}{answer} = <STDIN>);
 }
[download]

Where the format is nothing more than "yes|no"

Thanks for any help that can be provided - yall rock =)

Comment on Exact pattern match? Download Code

Replies are listed 'Best First'.
(jeffa) Re: Exact pattern match? by jeffa (Bishop) on Jan 19, 2001 at 01:45 UTC
Remember that /yes/ will match 'yes' as well as 'yessir' and also 'grayest' - what you need is word boundries: \b So change "yes\|no" to '\byes\b\|\bno\b' - and notice the single quotes - NOT double quotes. And we don't rock - we RAWK!! Jeff L-LL-L--L-LL-L--L-LL-L-- -R--R-RR-R--R-RR-R--R-RR F--F--F--F--F--F--F--F-- (the triplet paradiddle)	[reply]
Re: Exact pattern match? by chipmunk (Parson) on Jan 19, 2001 at 01:47 UTC
`$string =~ /^(?:yes\|no)\z/;` \z, unlike $ or \Z, won't match before a newline at the end of the string. If you've already chomped your data or don't care about a final newline, you can use $ instead. Refer to perlre for more on anchors in regular expressions.	[reply] [d/l]
Re: Exact pattern match? by swiftone (Curate) on Jan 19, 2001 at 01:44 UTC
Two options. You could either replace your regex with an eq operation, or you could use the ^ and $ patterns in your regex, which match the beginning or the end of the line. Since you're looking for something terribly exact, I'd recommend using eq.	[reply]
Re: Exact pattern match? by c-era (Curate) on Jan 19, 2001 at 01:45 UTC
If you are looking for 'yes' or 'no' I would suggest doing an 'eq'. If you need to get yes or no out of 'yes I can' or 'no I can't' then you may want to add some white space checking to your regex `/(^\|\s)(yes\|no)(\s\|$)/`. The 'eq' will be faster.	[reply] [d/l]
Re: Exact pattern match? by adamsj (Hermit) on Jan 19, 2001 at 02:48 UTC
The other advice is good, but I'll throw in a question: Do you have to allow for uppercasing, like Yes and No? If so, you've got some additional work to do. There are many ways to do it--my suggestion is to either lowercase the input with lc() before testing (if you're using eq) or to use the /i switch (if you're using the =~ operator). There are other ways, but I'd suggest these.	[reply]