I have this Expression
(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)
that is working fine in java but when i am trying to use the same in mySql it is giving me
Error Code: 1139
Got error 'repetition-operator operand invalid' from regexp
So when i replace above Expression with this
(((^25[0-5])|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}((^25[0-5])|2[0-4][0-9]|[01]?[0-9][0-9]?)
This is giving me some additional Results?
Plz let me know what i am Doing Wrong , Thanks For your time
The construct ?: is a non-capturing group.
When refering to the current documentation of MySQL one can see that it
is aimed at conformance with POSIX 1003.2
and that
MySQL uses the extended version
In other words, it uses POSIX ERE and this flavor simply doesn't support non-capturing groups.
For a detailed listing on what constructs are available in Java and in POSIX ERE you can use regular-expressions.info as a reference, specifically this site for capturing groups (just be sure to choose Java and POSIX ERE in the two dropdowns).
As to why you get additional results:
Did you notice that your regexes aren't equal?
In the first and second half of your first regex you write (?:25[0-5]|, while in the second regex this becomes ((^25[0-5])|.
A ^ matches the beginning of a string (here's the documentation again), so at least the second occurence can never match if anything was matched before.
Perhaps you want to use this regex in MySQL, but i can only take a guess here as i don't know your data and what exactly you want to match.
((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)
I just took your first regex and removed all ?:.
Related
This question already has answers here:
Regular expression to stop at first match
(9 answers)
Closed 2 years ago.
I have this gigantic ugly string:
J0000000: Transaction A0001401 started on 8/22/2008 9:49:29 AM
J0000010: Project name: E:\foo.pf
J0000011: Job name: MBiek Direct Mail Test
J0000020: Document 1 - Completed successfully
I'm trying to extract pieces from it using regex. In this case, I want to grab everything after Project Name up to the part where it says J0000011: (the 11 is going to be a different number every time).
Here's the regex I've been playing with:
Project name:\s+(.*)\s+J[0-9]{7}:
The problem is that it doesn't stop until it hits the J0000020: at the end.
How do I make the regex stop at the first occurrence of J[0-9]{7}?
Make .* non-greedy by adding '?' after it:
Project name:\s+(.*?)\s+J[0-9]{7}:
Using non-greedy quantifiers here is probably the best solution, also because it is more efficient than the greedy alternative: Greedy matches generally go as far as they can (here, until the end of the text!) and then trace back character after character to try and match the part coming afterwards.
However, consider using a negative character class instead:
Project name:\s+(\S*)\s+J[0-9]{7}:
\S means “everything except a whitespace and this is exactly what you want.
Well, ".*" is a greedy selector. You make it non-greedy by using ".*?" When using the latter construct, the regex engine will, at every step it matches text into the "." attempt to match whatever make come after the ".*?". This means that if for instance nothing comes after the ".*?", then it matches nothing.
Here's what I used. s contains your original string. This code is .NET specific, but most flavors of regex will have something similar.
string m = Regex.Match(s, #"Project name: (?<name>.*?) J\d+").Groups["name"].Value;
I would also recommend you experiment with regular expressions using "Expresso" - it's a utility a great (and free) utility for regex editing and testing.
One of its upsides is that its UI exposes a lot of regex functionality that people unexprienced with regex might not be familiar with, in a way that it would be easy for them to learn these new concepts.
For example, when building your regex using the UI, and choosing "*", you have the ability to check the checkbox "As few as possible" and see the resulting regex, as well as test its behavior, even if you were unfamiliar with non-greedy expressions before.
Available for download at their site:
http://www.ultrapico.com/Expresso.htm
Express download:
http://www.ultrapico.com/ExpressoDownload.htm
(Project name:\s+[A-Z]:(?:\\w+)+.[a-zA-Z]+\s+J[0-9]{7})(?=:)
This will work for you.
Adding (?:\\w+)+.[a-zA-Z]+ will be more restrictive instead of .*
This question already has answers here:
Regular expression to stop at first match
(9 answers)
Closed 2 years ago.
I have this gigantic ugly string:
J0000000: Transaction A0001401 started on 8/22/2008 9:49:29 AM
J0000010: Project name: E:\foo.pf
J0000011: Job name: MBiek Direct Mail Test
J0000020: Document 1 - Completed successfully
I'm trying to extract pieces from it using regex. In this case, I want to grab everything after Project Name up to the part where it says J0000011: (the 11 is going to be a different number every time).
Here's the regex I've been playing with:
Project name:\s+(.*)\s+J[0-9]{7}:
The problem is that it doesn't stop until it hits the J0000020: at the end.
How do I make the regex stop at the first occurrence of J[0-9]{7}?
Make .* non-greedy by adding '?' after it:
Project name:\s+(.*?)\s+J[0-9]{7}:
Using non-greedy quantifiers here is probably the best solution, also because it is more efficient than the greedy alternative: Greedy matches generally go as far as they can (here, until the end of the text!) and then trace back character after character to try and match the part coming afterwards.
However, consider using a negative character class instead:
Project name:\s+(\S*)\s+J[0-9]{7}:
\S means “everything except a whitespace and this is exactly what you want.
Well, ".*" is a greedy selector. You make it non-greedy by using ".*?" When using the latter construct, the regex engine will, at every step it matches text into the "." attempt to match whatever make come after the ".*?". This means that if for instance nothing comes after the ".*?", then it matches nothing.
Here's what I used. s contains your original string. This code is .NET specific, but most flavors of regex will have something similar.
string m = Regex.Match(s, #"Project name: (?<name>.*?) J\d+").Groups["name"].Value;
I would also recommend you experiment with regular expressions using "Expresso" - it's a utility a great (and free) utility for regex editing and testing.
One of its upsides is that its UI exposes a lot of regex functionality that people unexprienced with regex might not be familiar with, in a way that it would be easy for them to learn these new concepts.
For example, when building your regex using the UI, and choosing "*", you have the ability to check the checkbox "As few as possible" and see the resulting regex, as well as test its behavior, even if you were unfamiliar with non-greedy expressions before.
Available for download at their site:
http://www.ultrapico.com/Expresso.htm
Express download:
http://www.ultrapico.com/ExpressoDownload.htm
(Project name:\s+[A-Z]:(?:\\w+)+.[a-zA-Z]+\s+J[0-9]{7})(?=:)
This will work for you.
Adding (?:\\w+)+.[a-zA-Z]+ will be more restrictive instead of .*
I've tried the answers I've found in SOF, but none supported here : https://regexr.com
I essentially have an .OPML file with a large number of podcasts and descriptions.
in the following format:
<outline text="Software Engineering Daily" type="rss" xmlUrl="http://softwareengineeringdaily.com/feed/podcast/" htmlUrl="http://softwareengineeringdaily.com" />
What regex I can use to so I can just get the title and the link:
Software Engineering Daily
http://softwareengineeringdaily.com/feed/podcast/
Brief
There are many ways to go about this. The best way is likely using an XML parser. I would definitely read this post that discusses use of regex, especially with XML.
As you can see there are many answers to your question. It also depends on which language you are using since regex engines differ. Some accept backreferences, whilst others do not. I'll post multiple methods below that work in different circumstances/for different regex flavours. You can probably piece together from the multiple regex methods below which parts work best for you.
Code
Method 1
This method works in almost any regex flavour (at least the normal ones).
This method only checks against the attribute value opening and closing marks of " and doesn't include the possibility for whitespace before or after the = symbol. This is the simplest solution to get the values you want.
See regex in use here
\b(text|xmlUrl)="[^"]*"
Similarly, the following methods add more value to the above expression
\b(text|xmlUrl)\s*=\s*"[^"]*" Allows whitespace around =
\b(text|xmlUrl)=(?:"[^"]*"|'[^']*') Allows for ' to be used as attribute value delimiter
As another alternative (following the comments below my answer), if you wanted to grab every attribute except specific ones, you can use the following. Note that I use \w, which should cover most attributes, but you can just replace this with whatever valid characters you want. \S can be used to specify any non-whitespace characters or a set such as [\w-] may be used to specify any word or hyphen character. The negation of the specific attributes occurs with (?!text|xmlUrl), which says don't match those characters. Also, note that the word boundary \b at the beginning ensures that we're matching the full attribute name of text and not the possibility of other attributes with the same termination such as subtext.
\b((?!text|xmlUrl)\w+)="[^"]*"
Method 2
This method only works with regex flavours that allow backreferences. Apparently JGsoft applications, Delphi, Perl, Python, Ruby, PHP, R, Boost, and Tcl support single-digit backreferences. Double-digit backreferences are supported by JGsoft applications, Delphi, Python, and Boost. Information according this article about numbered backreferences from Regular-Expressions.info
See regex in use here
This method uses a backreference to ensure the same closing mark is used at the start and end of the attribute's value and also includes the possibility of whitespace surrounding the = symbol. This doesn't allow the possibility for attributes with no delimiter specified (using xmlUrl=http://softwareengineeringdaily.com/feed/podcast/ may also be valid).
See regex in use here
\b(text|xmlUrl)\s*=\s*(["'])(.*?)\2
Method 3
This method is the same as Method 2 but also allows attributes with no delimiters (note that delimiters are now considered to be space characters, thus, it will only match until the next space).
See regex in use here
\b(text|xmlUrl)\s*=\s*(?:(["'])(.*?)\2|(\S*))
Method 4
While Method 3 works, some people might complain that the attribute values might either of 2 groups. This can be fixed by either of the following methods.
Method 4.A
Branch reset groups are only possible in a few languages, notably JGsoft V2, PCRE 7.2+, PHP, Delphi, R (with PCRE enabled), Boost 1.42+ according to Regular-Expressions.info
This also shows the method you would use if backreferences aren't possible and you wanted to match multiple delimiters ("([^"])"|'([^']*))
See regex in use here
\b(text|xmlUrl)\s*=\s*(?|"([^"]*)"|'([^']*)'|(\S*))
Method 4.B
Duplicate subpatterns are not often supported. See this Regular-Expresions.info article for more information
This method uses the J regex flag, which allows duplicate subpattern names ((?<v>) is in there twice)
See regex in use here
\b(text|xmlUrl)\s*=\s*(?:(["'])(?<v>.*?)\2|(?<v>\S*))
Results
Input
<outline text="Software Engineering Daily" type="rss" xmlUrl="http://softwareengineeringdaily.com/feed/podcast/" htmlUrl="http://softwareengineeringdaily.com" />
Output
Each line below represents a different group. New matches are separated by two lines.
text
Software Engineering Daily
xmlUrl
http://softwareengineeringdaily.com/feed/podcast/
Explanation
I'll explain different parts of the regexes used in the Code section that way you understand the usage of each of these parts. This is more of a reference to the methods above.
"[^"]*" This is the fastest method possible (to the best of my knowledge) to grabbing anything between two " symbols. Note that it does not check for escaped backslashes, it will match any non-" character between two ". Whilst "(.*?)" can also be used, it's slightly slower
(["'])(.*?)\2 is basically shorthand for "(.*?)"|'(.*?)'. You can use any of the following methods to get the same result:
(?:"(.*?)"|'(.*?)')
(?:"([^"])"|'([^']*)') <-- slightly faster than line above
(?|) This is a branch reset group. When you place groups inside it like (?|(x)|(y)) it returns the same group index for both matches. This means that if x is captured, it'll get group index of 1, and if y is captured, it'll also get a group index of 1.
For simple HTML strings you might get along with
Url=(['"])(.+?)\1
Here, take group $2, see a demo on regex101.com.
Obligatory: consider using a parser instead (see here).
Why does this issue a badmatch error? I can't figure out why this would fail:
<<IpAddr, ":*:*">> = <<"2a01:e34:ee8b:c080:a542:ffaf:*:*">>.
You need to specify the size of IpAddr so that it can be pattern-matched:
1> <<IpAddr:28/binary, ":*:*">> = <<"2a01:e34:ee8b:c080:a542:ffaf:*:*">>.
<<"2a01:e34:ee8b:c080:a542:ffaf:*:*">>
2> IpAddr.
<<"2a01:e34:ee8b:c080:a542:ffaf">>
Pattern matching of a binary proceeds left-to-right so it will match IpAddr first before it tries the following segment. There is no back-tracking until there is a match. A default typed variable like IpAddr matches one byte. See Bit Syntax Expressions and Bit Syntax for a proper description and more examples.
As alternative to using pattern matching here you might consider using the binary module. There are two functions which could be useful to you: binary:match/2/3 and binary:split/2/3. These search which may better fit your problem.
As a last alternative you could try using regular expressions and the re module.
Really getting into MySQL and one thought I've had on mastering one aspect of it is to gather a complete listing of MySQL words. One example of this might be the Reserved Words list, though it appears that's not a complete list; example: CONCAT, CRC32, etc.
Bizarre as it may seem, I was thinking that such a list might exist, or that there might even be a query that would yield it, and/or a way to extract it from the source code of MySQL.
It is a non-scientific method, but what I would do is:
extract all strings from Native_func_registry func_array. Lookup for it sql/item_create.cc , e.g in
http://bazaar.launchpad.net/~mysql/mysql-server/mysql-trunk/view/head:/sql/item_create.cc
Those should cover builtin functions.
extract strings from 'symbols' and 'functions' in lexer :
http://bazaar.launchpad.net/~mysql/mysql-server/mysql-trunk/view/head:/sql/lex.h
extract symbols from bison input http://bazaar.launchpad.net/~mysql/mysql-server/mysql-trunk/view/head:/sql/sql_yacc.yy from lines
%token SOMETOKEN
except when tokens have _SYM suffix (they are covered by sql/lex.h)
Combine all of those, and the resulting set might come near :)