Regular Expression match too much

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

I have an perl web application that has to parse data from a customer for 'correctness'. One of the checks I use is something like:

$criteria = "HE|NP|OT|RF|SM";

if ($customer_data =~ m/$criteria/) {
  process_as_good()
} else {
  proc4ess_as_bad()
}
[download]

Obviously this matches for $customer_data = HE, NP, OT, RF, or SM which is the desired behavior. Unfortunately it will also match combinations like SMNP which is not desired. I seem to recall reading about a technique for this but I cannot find it again. Is it just my faulty memory or is there a clever way to make Perl match on the entire string and not just on a substring?

Comment on Regular Expression match too much Download Code

Replies are listed 'Best First'.
Re: Regular Expression match too much by ikegami (Patriarch) on Feb 08, 2006 at 19:36 UTC
`m/^(?:$criteria)\z/` Ref: perlre	[reply] [d/l] [select]
Re^2: Regular Expression match too much by Roy Johnson (Monsignor) on Feb 08, 2006 at 20:13 UTC
N.B.: If `$criteria` were a precompiled regex rather than a string being interpolated, the grouping parentheses would not be necessary. Caution: Contents may have been coded under pressure.	[reply] [d/l]
Re^2: Regular Expression match too much by enemyofthestate (Monk) on Feb 08, 2006 at 20:11 UTC
`m/^(?:$criteria)\z/` [download] That was it! Thank you.	[reply] [d/l]
Re^2: Regular Expression match too much by thor (Priest) on Feb 08, 2006 at 20:35 UTC
Just out of curiostiy, why did you use \z and with ^ instead of \A? thor `The only easy day was yesterday`	[reply]
Re^3: Regular Expression match too much by ikegami (Patriarch) on Feb 08, 2006 at 20:41 UTC
Little code &mdash I don't recall ever seeing any &mdash uses `\A` and `\Z` for regexps without `/m`. This is probably because the alternatives `^` and `$` stand out more. I didn't see any reason for breaking this convention. If `\a` was an alias for `\A`, I would have used that.	[reply] [d/l] [select]
Re: Regular Expression match too much by GrandFather (Saint) on Feb 08, 2006 at 19:44 UTC
`m/\b$criteria\b/` - require a word break at each end of the text. Allows matches on 'SM and other stuff' or 'SM NP', but not on 'SMNP'. DWIM is Perl's answer to Gödel	[reply] [d/l]
Re^2: Regular Expression match too much by ikegami (Patriarch) on Feb 08, 2006 at 20:08 UTC
Nice tip, but that should be `m/\b(?:$criteria)\b/`. `print('BOTTOM' =~ m/\b$criteria\b/ ?1:0, "\n"); # 1 print('BOTTOM' =~ m/\b(?:$criteria)\b/ ?1:0, "\n"); # 0` [download]	[reply] [d/l] [select]
Re^3: Regular Expression match too much by GrandFather (Saint) on Feb 08, 2006 at 20:11 UTC
Hmm, sneeky. I come here to learn, I learned :). Thankyou. DWIM is Perl's answer to Gödel	[reply]
Re: Regular Expression match too much by Cody Pendant (Prior) on Feb 09, 2006 at 00:09 UTC
Random thought -- if it's a web form you could set the maximum characters of the field to 2. That would diminish the possibilities for error. ($_='kkvvttuu bbooppuuiiffss qqffssmm iibbddllffss') =~y~b-v~a-z~s; print	[reply]
Re^2: Regular Expression match too much by enemyofthestate (Monk) on Feb 09, 2006 at 12:24 UTC
The data is parsed from an XML document. I have no control over what the customer puts in it so I have to do a lot of sanity checking	[reply]


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