Combine Regexp

Question

After collecting user input for various conditions like   Starts with          Ends with          Contains       Doesn t contains   To make single regex if user enter multiple conditions  I combine them with     so if 1 and 2 given it become              This method works so far but   I m not able to determine correctly  What should be regex for 4 the condition  And combining regex this way work        Update    user input  won t be same   for two conditions and not all four   conditions always present but they can   be and in future I might need more   conditions like  is exactly  and  is   exactly not  etc  so  I m more curious   to know this approach will scale        Also there may be issues of user input   cleanup so regex escaped properly  but   that is ignored right now

User · Answer

In my experience with regex you really need to focus on what EXACTLY you are trying to match, rather than what NOT to match.

for example

\d{2}

[1-9][0-9]

The first expression will match any 2 digits....and the second will match 1 digit from 1 to 9 and 1 digit - any digit. So if you type 07 the first expression will validate it, but the second one will not.

See this for advanced reference:

http://www.regular-expressions.info/refadv.html

EDITED:

^((?!my string).)*$ Is the regular expression for does not contain "my string".

User · Answer

Combining the regex for the fourth option with any of the others doesn t work within one regex   4   1 would mean either the string starts with   or doesn t contain   at all   You re going to need two separate comparisons to do that

User · Answer

If a string must not contain    every character must be another character than                 This will match any string of any length that does not contain     Another possible solution would be to invert the boolean result of

User · Answer

1   2   4 conditions  starts ends  but not in the middle                            is almost the same that                   but this one matches any string without    sample  my name is hal9000

User · Answer

Doesn t contain                 Combining works if the intended result of combination is that any of them matching results in the whole regexp matching

User · Answer

Will the conditions be ORed or ANDed together   Starts with  abc Ends with  xyz Contains  123 Doesn t contain  456   The OR version is fairly simple  as you said  it s mostly a matter of inserting pipes between individual conditions   The regex simply stops looking for a match as soon as one of the alternatives matches     abc xyz  123        456         That fourth alternative may look bizarre  but that s how you express  doesn t contain  in a regex   By the way  the order of the alternatives doesn t matter  this is effectively the same regex    xyz         456      123  abc    The AND version is more complicated   After each individual regex matches  the match position has to be reset to zero so the next regex has access to the whole input  That means all of the conditions have to be expressed as lookaheads  technically  one of them doesn t have to be a lookahead  I think it expresses the intent more clearly this way    A final     consummates the match         abc      xyz       123           456             And then there s the possibility of combined AND and OR conditions--that s where the real fun starts   D

[regex] Combine Regexp?

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