I have a list of words and I need to fine the ones that do not contain certain characters (or only contain other certain characters, whichever is easier).  I have done this a couple of years ago, but need to do it again and my memory fails me.

your question is too generic. Pls read our PostingGuidelines and provide more details on what you are trying to accomplish.

Sample list of words:

golf

fort

flag

frog

 I need a regex to find the words that do not contain a or g.  This should match only fort.

To be specific, I have a dictionary in a mysql db and want to get a list of words that can be generated by only using the top row of keys (qwertyuiop).

if you are matching the words separately , as individual string, this shoud do it:

^[^ag]+$

Great, that works.

 

Here is another one.  is possible to do a match on a word to see if it follows a pattern like consonant, vowel, consoant like banana, or coke?

^([bcdefgnm][aeoue])+$

enhance the first container [] to include all consonants.

Fantastic!

 

Here is the results of these regex expressions

 

http://www.patricklewis.net/games/dropwords/DictCheck.php

 

hey I am also in a similar situation.

I need to validate user input. This is how I do.

/^[\w\._-]{5,10}$/

This allows a periods, underscores, hypens, any alphanumerics and its length should be in range of 5-10

Now I need to blacklist certain key words like 'drop' 'delete' insert' etc. which should not be allowed

/^[\w\._-]{5,10}$/

This allows a periods, underscores, hypens, any alphanumerics and its length should be in range of 5-10

Now I need to blacklist certain key words like 'drop' 'delete' insert' etc. which should not be allowed

How do I add this extra condition checking to the above expression??

I tried adding this ^[^drop|delete|insert]+$ to the above expression which results in

/^[\w\._-]{5,10}^[^drop|delete|insert]+$/       but this doesn't work

Sergei Z, plz help me.

 Thanks in advance.

pls specify your platform/programming language/tool. Regex syntax/solution, much like any other type of code, depends on these.

 

The [...] defines a set of characters, not a set of words. Probably what you want is a negative lookahead:

    /^(?!drop|delete|insert)[\w\._-]{5,10}$/

Actually, there's no need to exclude "drop", because you're restricting the number of characters to between 5 and 10, and "drop" has only 4.

By the way, judging from the list of words you want to blacklist, it looks like your intention may be to use regex to stop SQL injection attacks. If that's the case, your approach is wrong. Any decent SQL implementation will have a way to put values safely into an SQL command or query.

Thanks for ur input guys.

@MRAB: You got it right. I am here trying to avoid sql injection. I know that parameterized queries are safe n secure. But I am just trying to bypass blacklisting approach.

And comin to the point, the regexp which you suggested works but it has some problems.

deleteadmi -> matches the regexp

adelete -> Doesn't match

To summarize, only if the blacklisted words are at the beggining of the string, it matches. If the string starts with any other character followed by blacklisted word, it doesn't match.

So what I did is this :    /^[\w\._-]+^(?!drop|delete|insert)[\w\._-]{5,10}$/

But this is also not working. Any idea?

 

The "^" matches only at the start of the string (or line if you're using multiline mode), so:

    /^[\w\._-]+^(?!drop|delete|insert)[\w\._-]{5,10}$/

is anchored at the start of the string, then matches a "word" (at least one character), then tries to match the string of the string again, but it's already at least one character beyond it, so no match.