Related
Introduction:
I have the following scenario in PostgreSQL whereby I want to perform some data validation on a .csv string prior to inserting it into a table (see the fiddle here).
I've managed to get a regex (in a CHECK constraint) which disallows spaces within strings (e.g. "12 34") and also disallows preceding zeros ("00343").
Now, the icing on the cake would be if I could use regular expressions to disallow strings which contain a repeat of an integer - i.e. if a sequence \d+ matched another \d+ within the same string.
Is this beyond the capacities of regular expressions?
My table is as follows:
CREATE TABLE test
(
data TEXT NOT NULL,
CONSTRAINT d_csv_only_ck
CHECK (data ~ '^([ ]*([1-9]\d*)+[ ]*)(,[ ]*([1-9]\d*)+[ ]*)*$')
);
And I can populate it as follows:
INSERT INTO test VALUES
('992,1005,1007,992,456,456,1008'), -- want to make this line unnacceptable - repeats!
('44,1005,1110'),
('13, 44 , 1005, 10078 '), -- acceptable - spaces before and after integers
('11,1203,6666'),
('1,11,99,2222'),
('3435'),
(' 1234 '); -- acceptable
But:
INSERT INTO test VALUES ('23432, 3433 ,00343, 567'); -- leading 0 - unnacceptable
fails (as it should), and also fails (again, as it should)
INSERT INTO test VALUES ('12 34'); -- spaces within numbers - unnacceptable
The question:
However, if you notice the first string, it has repeats of 992and 456.
I would like to be able to match these.
All of these rules do not have to be in the same regex - I can use a second CHECK constraint.
I would like to know if what I am asking is possible using Regular Expressions?
I did find this post which appears to go some (all?) of the way to solving my issue, but I'm afraid it's beyond my skillset to get it to work - I've included a small test at the bottom of the fiddle.
Please let me know should you require any further information.
p.s. as an aside, I'm not very experienced with regexes and I would welcome any input on my basic one above.
Since PostegreSQL regex does not support backreferences, you cannot apply this restriction because you would need a negative lookahead with a backreference in it.
Have a look at this PCRE regex:
^(?!.*\b(\d+)\b.*\b\1\b) *[1-9]\d* *(?:, *[1-9]\d* *)*$
See this regex demo.
Details:
^ - start of string
(?!.*\b(\d+)\b.*\b\1\b) - no same two numbers as whole word allowed anywhere in the string
* - zero or more spaces
[1-9]\d* - a non-zero digit and then any zero or more digits
* - zero or more spaces
(?:, *[1-9]\d* *)* - zero or more occurrences of
, * - comma and zero or more spaces
[1-9]\d* - a non-zero digit and then any zero or more digits
* - zero or more spaces
$ - end of string.
Even if you replace \b with \y (PostgreSQL regex word boundaries) in the PostgreSQL code, it won't work due to the drawback mentioned at the top of the answer.
This is adapted from an online dataset referencing "Customer Complaints". The data was modified in Excel and Notepad++. This manipulation produced an "extra" set of quotes directly following each "index digit" [1,2,3 ...] directly after the string, "VALUES (X". I would like to remove only this "extra quotes" and maintain the sequential index numbers, which range from a single digit to a number having five digits. This is in preparation to working with a proprietary database having 1.35 million lines of code.
This rather clumsy adaptation of Regex will "find" a string containing the quotes but a "replace" code which maintains the indexing numbers eludes me. Any help would be appreciated.
REGEX
\s\(([0-9])",|\s\(([0-9][0-9])",|\s\(([0-9][0-9][0-9])",|\s\(([0-9][0-9][0-9][0-9])",|\s\(([0-9][0-9][0-9][0-9][0-9])",
DATA STRINGS
INSERT INTO Complaints VALUES (1","2013-07-29","consumer loan","managing the loan or lease","Wells Fargo & Company","VA","24540","phone","2013-07-30","closed with explanation","468882");
INSERT INTO Complaints VALUES (2","2013-07-29","bank account or service","using a debit or ATM card","Wells Fargo & Company","CA","95992","web","2013-07-31","closed with explanation","468889");
INSERT INTO Complaints VALUES (3","2013-07-29","bank account or service","account opening, closing, or management","Santander Bank US","NY","10065","fax","2013-07-31","closed","468879");
Find VALUES \((\d+)" - the inner parentheses will capture the digits (\d) one or more times (+) until a " is encountered.
You can then replace with VALUES \($1 where $1 is the corresponding captured value.
Ctrl+H
Find what: VALUES\h*\(\d+\K"
Replace with: LEAVE EMPTY
check Wrap around
check Regular expression
Replace all
Explanation:
VALUES # literally
\h* # 0 or more horizontal spaces
\( # opening parenthesis
\d+ # 1 or more digits
\K # forget all we have seen until this position
" # a double quote
Screen capture:
I am trying to extract words after the first space using
species<-gsub(".* ([A-Za-z]+)", "\1", x=genus)
This works fine for the other rows that have two words, however row [9] "Eulamprus tympanum marnieae" has 3 words and my code is only returning the last word in the string "marnieae". How can I extract the words after the first space so I can retrieve "tympanum marnieae" instead of "marnieae" but have the answers stored in one variable called >species.
genus
[9] "Eulamprus tympanum marnieae"
Your original pattern didn't work because the subpattern [A-Za-z]+ doesn't match spaces, and therefore will only match a single word.
You can use the following pattern to match any number of words (other than 0) after the first, within double quotes:
"[A-Za-z]+ ([A-Za-z ]+)" https://regex101.com/r/p6ET3I/1
https://regex101.com/r/p6ET3I/2
This is a relatively simple, but imperfect, solution. It will also match trailing spaces, or just one or more spaces after the first word even if a second word doesn't exist. "Eulamprus " for example will successfully match the pattern, and return 5 spaces. You should only use this pattern if you trust your data to be properly formatted.
A more reliable approach would be the following:
"[A-Za-z]+ ([A-Za-z]+(?: [A-Za-z]+)*)"
https://regex101.com/r/p6ET3I/3
This pattern will capture one word (following the first), followed by any number of addition words (including 0), separated by spaces.
However, from what I remember from biology class, species are only ever comprised of one or two names, and never capitalized. The following pattern will reflect this format:
"[A-Za-z]+ ([a-z]+(?: [a-z]+)?)"
https://regex101.com/r/p6ET3I/4
In the course of processing a large textual chemical database with Perl, I had been faced with the problem of using a regex to match chemical formulae. I have seen these two previous topics, but the suggested answers there are too loose for my requirements.
Specifically, my (admittedly limited) research has led me to this posting that gives a regex for the currently accepted chemical symbols, which I'll copy here for reference
[BCFHIKNOPSUVWY]|[ISZ][nr]|[ACELP][ru]|A[cglmst]|B[aehikr]|C[adeflos]|D[bsy]|Es|F[elmr]|G[ade]|H[efgos]|Kr|L[aiv]|M[cdgnot]|N[abdehiop]|O[gs]|P[abdmot]|R[abe-hnu]|S[bcegim]|T[abcehilms]|Xe|Yb
(Thus e.g. C, Cm, and Cn will pass, but not Cg or Cx.)
As with the previous questions, I also need to match numbers, complete sets of parentheses and complete sets of square brackets, so that both e.g. C2H6O and (CH3)2CFCOO(CH2)2Si(CH3)2Cl are matched.
So how do I combine the previous solutions with the grand regex for matching valid chemical elements to strictly match a chemical formula?
(If it's not too much trouble to add, a blow-by-blow account of how to humanly parse the regex would be appreciated greatly, though not strictly necessary.)
Brief
I decided why not create a massive regex to do what you want (but still maintain a clean regex). This regex would be used in conjunction with a loop to go over matches for bracket or parentheses groups.
Assumptions
I am assuming the following since the OP has not given a full list of positive and negative matches:
Nested parentheses aren't possible
Nested square brackets aren't possible
Square bracket groups that surround a single parentheses group are redundant and therefore incorrect
Square bracket groups must contain at least 2 groups, of which 1 such group must be a parentheses group
If any of these assumptions are incorrect, please let me know so that I may fix the regex accordingly
Answer
View this regex in use here
Code
(?(DEFINE)
(?# Periodic elements )
(?<Hydrogen>H)
(?<Helium>He)
(?<Lithium>Li)
(?<Beryllium>Be)
(?<Boron>B)
(?<Carbon>C)
(?<Nitrogen>N)
(?<Oxygen>O)
(?<Fluorine>F)
(?<Neon>Ne)
(?<Sodium>Na)
(?<Magnesium>Mg)
(?<Aluminum>Al)
(?<Silicon>Si)
(?<Phosphorus>P)
(?<Sulfur>S)
(?<Chlorine>Cl)
(?<Argon>Ar)
(?<Potassium>K)
(?<Calcium>Ca)
(?<Scandium>Sc)
(?<Titanium>Ti)
(?<Vanadium>V)
(?<Chromium>Cr)
(?<Manganese>Mn)
(?<Iron>Fe)
(?<Cobalt>Co)
(?<Nickel>Ni)
(?<Copper>Cu)
(?<Zinc>Zn)
(?<Gallium>Ga)
(?<Germanium>Ge)
(?<Arsenic>As)
(?<Selenium>Se)
(?<Bromine>Br)
(?<Krypton>Kr)
(?<Rubidium>Rb)
(?<Strontium>Sr)
(?<Yttrium>Y)
(?<Zirconium>Zr)
(?<Niobium>Nb)
(?<Molybdenum>Mo)
(?<Technetium>Tc)
(?<Ruthenium>Ru)
(?<Rhodium>Rh)
(?<Palladium>Pd)
(?<Silver>Ag)
(?<Cadmium>Cd)
(?<Indium>In)
(?<Tin>Sn)
(?<Antimony>Sb)
(?<Tellurium>Te)
(?<Iodine>I)
(?<Xenon>Xe)
(?<Cesium>Cs)
(?<Barium>Ba)
(?<Lanthanum>La)
(?<Cerium>Ce)
(?<Praseodymium>Pr)
(?<Neodymium>Nd)
(?<Promethium>Pm)
(?<Samarium>Sm)
(?<Europium>Eu)
(?<Gadolinium>Gd)
(?<Terbium>Tb)
(?<Dysprosium>Dy)
(?<Holmium>Ho)
(?<Erbium>Er)
(?<Thulium>Tm)
(?<Ytterbium>Yb)
(?<Lutetium>Lu)
(?<Hafnium>Hf)
(?<Tantalum>Ta)
(?<Tungsten>W)
(?<Rhenium>Re)
(?<Osmium>Os)
(?<Iridium>Ir)
(?<Platinum>Pt)
(?<Gold>Au)
(?<Mercury>Hg)
(?<Thallium>Tl)
(?<Lead>Pb)
(?<Bismuth>Bi)
(?<Polonium>Po)
(?<Astatine>At)
(?<Radon>Rn)
(?<Francium>Fr)
(?<Radium>Ra)
(?<Actinium>Ac)
(?<Thorium>Th)
(?<Protactinium>Pa)
(?<Uranium>U)
(?<Neptunium>Np)
(?<Plutonium>Pu)
(?<Americium>Am)
(?<Curium>Cm)
(?<Berkelium>Bk)
(?<Californium>Cf)
(?<Einsteinium>Es)
(?<Fermium>Fm)
(?<Mendelevium>Md)
(?<Nobelium>No)
(?<Lawrencium>Lr)
(?<Rutherfordium>Rf)
(?<Dubnium>Db)
(?<Seaborgium>Sg)
(?<Bohrium>Bh)
(?<Hassium>Hs)
(?<Meitnerium>Mt)
(?<Darmstadtium>Ds)
(?<Roentgenium>Rg)
(?<Copernicium>Cn)
(?<Nihonium>Nh)
(?<Flerovium>Fl)
(?<Moscovium>Mc)
(?<Livermorium>Lv)
(?<Tennessine>Ts)
(?<Oganesson>Og)
(?# Regex )
(?<Element>(?&Actinium)|(?&Silver)|(?&Aluminum)|(?&Americium)|(?&Argon)|(?&Arsenic)|(?&Astatine)|(?&Gold)|(?&Barium)|(?&Beryllium)|(?&Bohrium)|(?&Bismuth)|(?&Berkelium)|(?&Bromine)|(?&Boron)|(?&Calcium)|(?&Cadmium)|(?&Cerium)|(?&Californium)|(?&Chlorine)|(?&Curium)|(?&Copernicium)|(?&Cobalt)|(?&Chromium)|(?&Cesium)|(?&Copper)|(?&Carbon)|(?&Dubnium)|(?&Darmstadtium)|(?&Dysprosium)|(?&Erbium)|(?&Einsteinium)|(?&Europium)|(?&Iron)|(?&Flerovium)|(?&Fermium)|(?&Francium)|(?&Fluorine)|(?&Gallium)|(?&Gadolinium)|(?&Germanium)|(?&Helium)|(?&Hafnium)|(?&Mercury)|(?&Holmium)|(?&Hassium)|(?&Hydrogen)|(?&Indium)|(?&Iridium)|(?&Iodine)|(?&Krypton)|(?&Potassium)|(?&Lanthanum)|(?&Lithium)|(?&Lawrencium)|(?&Lutetium)|(?&Livermorium)|(?&Moscovium)|(?&Mendelevium)|(?&Magnesium)|(?&Manganese)|(?&Molybdenum)|(?&Meitnerium)|(?&Sodium)|(?&Niobium)|(?&Neodymium)|(?&Neon)|(?&Nihonium)|(?&Nickel)|(?&Nobelium)|(?&Neptunium)|(?&Nitrogen)|(?&Oganesson)|(?&Osmium)|(?&Oxygen)|(?&Protactinium)|(?&Lead)|(?&Palladium)|(?&Promethium)|(?&Polonium)|(?&Praseodymium)|(?&Platinum)|(?&Plutonium)|(?&Phosphorus)|(?&Radium)|(?&Rubidium)|(?&Rhenium)|(?&Rutherfordium)|(?&Roentgenium)|(?&Rhodium)|(?&Radon)|(?&Ruthenium)|(?&Antimony)|(?&Scandium)|(?&Selenium)|(?&Seaborgium)|(?&Silicon)|(?&Samarium)|(?&Tin)|(?&Strontium)|(?&Sulfur)|(?&Tantalum)|(?&Terbium)|(?&Technetium)|(?&Tellurium)|(?&Thorium)|(?&Titanium)|(?&Thallium)|(?&Thulium)|(?&Tennessine)|(?&Uranium)|(?&Vanadium)|(?&Tungsten)|(?&Xenon)|(?&Ytterbium)|(?&Yttrium)|(?&Zirconium)|(?&Zinc))
(?<Num>(?:[1-9]\d*)?)
(?<ElementGroup>(?:(?&Element)(?&Num))+)
(?<ElementParenthesesGroup>\((?&ElementGroup)+\)(?&Num))
(?<ElementSquareBracketGroup>\[(?:(?:(?&ElementParenthesesGroup)(?:(?&ElementGroup)|(?&ElementParenthesesGroup))+)|(?:(?:(?&ElementGroup)|(?&ElementParenthesesGroup))+(?&ElementParenthesesGroup)))\](?&Num))
)
^((?<Brackets>(?&ElementSquareBracketGroup))|(?<Parentheses>(?&ElementParenthesesGroup))|(?<Group>(?&ElementGroup)))+$
Explanation
The first part of the (?(DEFINE)) section lists each periodic element (ordered by atomic number for easy lookup).
The Element group acts as a simple or | between each of the elements listed in 1. ensuring that each element's symbol is ordered alphabetically by the first character, and then by symbol character length (so as not to catch, for example, Carbon C instead of Calcium Ca)
ElementGroup specifies a group of chemicals in the format: one or more Element followed by zero or more digits, excluding zero (specified by the group Num)
Valid Examples
C - Element
CH - Element followed by another Element
CH3 -Element followed by another Element and a Num
O2 - Element followed by a Num
Invalid Examples
N0 - 0 cannot be used explicitly
N01 - Num group specifies the number must begin with 1-9 or not have a number
A - Element does not exist
c - Element does not exist - case sensitive regex
ElementParenthesesGroup specifies one or more groupings of ElementGroup between parentheses ( ) but containing at least one ElementGroup
Valid Examples
(CH) - ElementGroup surrounded by parentheses
(CH3) - ElementGroup surrounded by parentheses
(CH3NO4) - multiple ElementGroup surrounded by parentheses
(CH3N04)2 - multiple ElementGroup surrounded by parentheses followed by a Num
Invalid Examples
(CH[NO4]) - Only ElementGroup is valid inside ElementParenthesesGroup
ElementSquareBracketGroup specifies a grouping of ElementParenthesesGroup or ElementGroup between square brackets [ ] but containing at least one ElementParenthesesGroup and one other group (ElementParenthesesGroup or ElementGroup)
Valid Examples
[CH3(NO4)] - Contains at least one ElementParenthesesGroup and one other ElementParenthesesGroup or ElementGroup
[(NO4)CH]2 - Contains at least one ElementParenthesesGroup and one other ElementParenthesesGroup or ElementGroup followed by Num
[(NO4)(CH3)] - Contains at least one ElementParenthesesGroup and one other ElementParenthesesGroup or ElementGroup
Invalid Examples
[(NO4)] - Does not contain second group, brackets [ ] are redundant
[NO4] - Does not contain ElementParenthesesGroup
Additional Information
I realize this is a very long answer, but the OP is asking a very specific question and wants to ensure specific criteria are met.
Ensure the following flags are set:
g - ensures global matches
x - ensures whitespace is ignored
if the data is across multiple lines (separated by a newline character) use m for multi line
Note: Regex will only capture the last group of type X that it finds (and overwrite the previously captured group of said type X. This is the default behaviour of regex and there is no way to currently override this behaviour. This may give you undesirable results. You can see this with the last example in the linked regex as well as with your example of (CH3)2CFCOO(CH2)2Si(CH3)2Cl since there are multiple of each group type.
It is best not to assemble such a large regex manually. Instead, let's assume we have an array of atoms #atoms. We can then create a regex matching any of these atoms like:
my ($atoms_regex) = map qr/$_/, join '|', map quotemeta, sort #atoms;
(Sort all items so that shorter atom names come first, then escape all items with quotemeta, join them with a | for alternatives, and compile the regex.)
You can add any used abbreviations to the #atoms array.
Next, we can write a regex that allows grouping and numbering. Our regex will match any number of items, where an item may be an atom or a group, and may be followed by a number:
my $chemical_formula_regex = qr/
(?&item)++
(?(DEFINE)
(?<item> (?: \((?&item)++\) | \[(?&item)++\] | $atoms_regex ) [0-9]* )
)
/x;
Within the (?(DEFINE) ...) group we can define named subpatterns with (?<name> ...). A subpattern is like a subroutine for a regex. We can call those subpatterns with (?&name). This allows us to structure the regex without unnecessary repetition.
The /x flag allows us to use whitespace and linebreaks and comments to lay out the regex in a more readable fashion. Regexes don't have to be an incomprehensible mess!
The ++ quantifier instead of + is not strictly necessary, but prevents unwanted backtracking. That may be a bit faster when a match fails.
Since this post is a top result for "regex chemistry symbols", I would also like to submit a solution. It is a python script that uses a regex to match chemistry formulas of the type A#B#, where A and B are chemical symbols and # is a number. The script as implemented matches and then surrounds the matches with \ce{} for use in LaTeX. It also includes the ability to exclude matches if the capture is in a user-defined list, which means words such as "I" and "In" will not be matched. Gist Link.
#!/usr/bin/env python3
# Find chemical symbols and surround them with \ce{ Symbol }
# Problem words: I, HOW, In, degrees K. Add words to exlist to ignore them.
import re, sys
if len(sys.argv) < 2 :
print('Usage:> {} <filename>'.format(sys.argv[0]))
sys.exit(1)
ptable =" H He "
ptable+=" Li Be B C N O F Ne "
ptable+=" Na Mg Al Si P S Cl Ar "
ptable+=" K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr "
ptable+=" Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe "
ptable+=" Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn "
ptable+=" Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og "
ptable+=" Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu "
ptable+=" Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr "
exlist = ['C','I','In','K','HOW'] # exclude these words from being replaced
orsyms = '|'.join(ptable.split())
resyms = re.compile(r'\b'+'((?:(?:{})\d*)+)'.format(orsyms)+r'\b')
latexfile=sys.argv[1]
with open(latexfile,'r') as fd:
for line in fd:
for m in list(set(resyms.findall(line))):
if m not in exlist :
line = re.sub(r'\b'+m+r'\b', r'\ce{'+m+r'}', line)
print(line,end='')
Beginner RegExp question. I have lines of JSON in a textfile, each with slightly different Fields, but there are 3 fields I want to extract for each line if it has it, ignoring everything else. How would I use a regex (in editpad or anywhere else) to do this?
Example:
"url":"http://www.netcharles.com/orwell/essays.htm",
"domain":"netcharles.com",
"title":"Orwell Essays & Journalism Section - Charles' George Orwell Links",
"tags":["orwell","writing","literature","journalism","essays","politics","essay","reference","language","toread"],
"index":2931,
"time_created":1345419323,
"num_saves":24
I want to extract URL,TITLE,TAGS,
/"(url|title|tags)":"((\\"|[^"])*)"/i
I think this is what you're asking for. I'll provide an explanation momentarily. This regular expression (delimited by / - you probably won't have to put those in editpad) matches:
"
A literal ".
(url|title|tags)
Any of the three literal strings "url", "title" or "tags" - in Regular Expressions, by default Parentheses are used to create groups, and the pipe character is used to alternate - like a logical 'or'. To match these literal characters, you'd have to escape them.
":"
Another literal string.
(
The beginning of another group. (Group 2)
(
Another group (3)
\\"
The literal string \" - you have to escape the backslash because otherwise it will be interpreted as escaping the next character, and you never know what that'll do.
|
or...
[^"]
Any single character except a double quote The brackets denote a Character Class/Set, or a list of characters to match. Any given class matches exactly one character in the string. Using a carat (^) at the beginning of a class negates it, causing the matcher to match anything that's not contained in the class.
)
End of group 3...
*
The asterisk causes the previous regular expression (in this case, group 3), to be repeated zero or more times, In this case causing the matcher to match anything that could be inside the double quotes of a JSON string.
)"
The end of group 2, and a literal ".
I've done a few non-obvious things here, that may come in handy:
Group 2 - when dereferenced using Backreferences - will be the actual string assigned to the field. This is useful when getting the actual value.
The i at the end of the expression makes it case insensitive.
Group 1 contains the name of the captured field.
EDIT: So I see that the tags are an array. I'll update the regular expression here in a second when I've had a chance to think about it.
Your new Regex is:
/"(url|title|tags)":("(\\"|[^"])*"|\[("(\\"|[^"])*"(,"(\\"|[^"])*")*)?\])/i
All I've done here is alternate the string regular expression I had been using ("((\\"|[^"])*)"), with a regular expression for finding arrays (\[("(\\"|[^"])*"(,"(\\"|[^"])*")*)?\]). No so easy to Read, is it? Well, substituting our String Regex out for the letter S, we can rewrite it as:
\[(S(,S)*)?\]
Which matches a literal opening bracket (hence the backslashes), optionally followed by a comma separated list of strings, and a closing bracket. The only new concept I've introduced here is the question mark (?), which is itself a type of repetition. Commonly referred to as 'making the previous expression optional', it can also be thought of as exactly 0 or 1 matches.
With our same S Notation, here's the whole dirty Regular Expression:
/"(url|title|tags)":(S|\[(S(,S)*)?\])/i
If it helps to see it in action, here's a view of it in action.
This question is a bit older, but I have had browsed a bit on my PC and found that expression. I passed him as GIST, could be useful to others.
EDIT:
# Expression was tested with PHP and Ruby
# This regular expression finds a key-value pair in JSON formatted strings
# Match 1: Key
# Match 2: Value
# https://regex101.com/r/zR2vU9/4
# http://rubular.com/r/KpF3suIL10
(?:\"|\')(?<key>[^"]*)(?:\"|\')(?=:)(?:\:\s*)(?:\"|\')?(?<value>true|false|[0-9a-zA-Z\+\-\,\.\$]*)
# test document
[
{
"_id": "56af331efbeca6240c61b2ca",
"index": 120000,
"guid": "bedb2018-c017-429E-b520-696ea3666692",
"isActive": false,
"balance": "$2,202,350",
"object": {
"name": "am",
"lastname": "lang"
}
}
]
the json string you'd like to extract field value from
{"fid":"321","otherAttribute":"value"}
the following regex expression extract exactly the "fid" field value "321"
(?<=\"fid\":\")[^\"]*
Please try below expression:
/"(url|title|tags)":("([^""]+)"|\[[^[]+])/gm
Explanation:
1st Capturing Group (url|title|tags): This is alternatively capturing the characters 'url','title' and 'tags' literally (case sensitive).
2nd Capturing Group ("([^""]+)"|[[^[]+]):
1st Alternative "([^""]+)" is matches all words within " and " including " and "
2nd Alternative [[^[]+] is matches all words within [ and ] including [ and ]
I have tested here
I adapted regex to work with JSON in my own library. I've detailed algorithm behavior below.
First, stringify the JSON object. Then, you need to store the starts and lengths of the matched substrings. For example:
"matched".search("ch") // yields 3
For a JSON string, this works exactly the same (unless you are searching explicitly for commas and curly brackets in which case I'd recommend some prior transform of your JSON object before performing regex (i.e. think :, {, }).
Next, you need to reconstruct the JSON object. The algorithm I authored does this by detecting JSON syntax by recursively going backwards from the match index. For instance, the pseudo code might look as follows:
find the next key preceding the match index, call this theKey
then find the number of all occurrences of this key preceding theKey, call this theNumber
using the number of occurrences of all keys with same name as theKey up to position of theKey, traverse the object until keys named theKey has been discovered theNumber times
return this object called parentChain
With this information, it is possible to use regex to filter a JSON object to return the key, the value, and the parent object chain.
You can see the library and code I authored at http://json.spiritway.co/
if your json is
{"key1":"abc","key2":"xyz"}
then below regex will extract key1 or key2 based on a key that you pass in regex
"key2(.*?)(?=,|}|$)
you can verify it here - regex101.com
Why does it have to be a Regular Expression object?
Here we can just use a Hash object first and then go search it.
mh = {"url":"http://www.netcharles.com/orwell/essays.htm","domain":"netcharles.com","title":"Orwell Essays & Journalism Section - Charles' George Orwell Links","tags":["orwell","writing","literature","journalism","essays","politics","essay","reference","language","toread"],"index":2931,"time_created":1345419323,"num_saves":24}
The output of which would be
=> {:url=>"http://www.netcharles.com/orwell/essays.htm", :domain=>"netcharles.com", :title=>"Orwell Essays & Journalism Section - Charles' George Orwell Links", :tags=>["orwell", "writing", "literature", "journalism", "essays", "politics", "essay", "reference", "language", "toread"], :index=>2931, :time_created=>1345419323, :num_saves=>24}
Not that I want to avoid using Regexp but don't you think it would be easier to take it a step at a time until your getting the data you want to further search through? Just MHO.
mh.values_at(:url, :title, :tags)
The output:
["http://www.netcharles.com/orwell/essays.htm", "Orwell Essays & Journalism Section - Charles' George Orwell Links", ["orwell", "writing", "literature", "journalism", "essays", "politics", "essay", "reference", "language", "toread"]]
Taking the pattern that FrankieTheKneeman gave you:
pattern = /"(url|title|tags)":"((\\"|[^"])*)"/i
we can search the mh hash by converting it to a json object.
/#{pattern}/.match(mh.to_json)
The output:
=> #<MatchData "\"url\":\"http://www.netcharles.com/orwell/essays.htm\"" 1:"url" 2:"http://www.netcharles.com/orwell/essays.htm" 3:"m">
Of course this is all done in Ruby which is not a tag that you have but relates I hope.
But oops! Looks like we can't do all three at once with that pattern so I will do them one at a time just for sake.
pattern = /"(title)":"((\\"|[^"])*)"/i
/#{pattern}/.match(mh.to_json)
#<MatchData "\"title\":\"Orwell Essays & Journalism Section - Charles' George Orwell Links\"" 1:"title" 2:"Orwell Essays & Journalism Section - Charles' George Orwell Links" 3:"s">
pattern = /"(tags)":"((\\"|[^"])*)"/i
/#{pattern}/.match(mh.to_json)
=> nil
Sorry about that last one. It will have to be handled differently.