Parse a MySQL insert statement with multiple rows [duplicate] - mysql

I need a regular expression to select all the text between two outer brackets.
Example:
START_TEXT(text here(possible text)text(possible text(more text)))END_TXT
^ ^
Result:
(text here(possible text)text(possible text(more text)))


I want to add this answer for quickreference. Feel free to update.
.NET Regex using balancing groups:
\((?>\((?<c>)|[^()]+|\)(?<-c>))*(?(c)(?!))\)
Where c is used as the depth counter.
Demo at Regexstorm.com
Stack Overflow: Using RegEx to balance match parenthesis
Wes' Puzzling Blog: Matching Balanced Constructs with .NET Regular Expressions
Greg Reinacker's Weblog: Nested Constructs in Regular Expressions
PCRE using a recursive pattern:
\((?:[^)(]+|(?R))*+\)
Demo at regex101; Or without alternation:
\((?:[^)(]*(?R)?)*+\)
Demo at regex101; Or unrolled for performance:
\([^)(]*+(?:(?R)[^)(]*)*+\)
Demo at regex101; The pattern is pasted at (?R) which represents (?0).
Perl, PHP, Notepad++, R: perl=TRUE, Python: PyPI regex module with (?V1) for Perl behaviour.
(the new version of PyPI regex package already defaults to this → DEFAULT_VERSION = VERSION1)
Ruby using subexpression calls:
With Ruby 2.0 \g<0> can be used to call full pattern.
\((?>[^)(]+|\g<0>)*\)
Demo at Rubular; Ruby 1.9 only supports capturing group recursion:
(\((?>[^)(]+|\g<1>)*\))
Demo at Rubular  (atomic grouping since Ruby 1.9.3)
JavaScript  API :: XRegExp.matchRecursive
XRegExp.matchRecursive(str, '\\(', '\\)', 'g');
Java: An interesting idea using forward references by #jaytea.
Without recursion up to 3 levels of nesting:
(JS, Java and other regex flavors)
To prevent runaway if unbalanced, with * on innermost [)(] only.
\((?:[^)(]|\((?:[^)(]|\((?:[^)(]|\([^)(]*\))*\))*\))*\)
Demo at regex101; Or unrolled for better performance (preferred).
\([^)(]*(?:\([^)(]*(?:\([^)(]*(?:\([^)(]*\)[^)(]*)*\)[^)(]*)*\)[^)(]*)*\)
Demo at regex101; Deeper nesting needs to be added as required.
Reference - What does this regex mean?
RexEgg.com - Recursive Regular Expressions
Regular-Expressions.info - Regular Expression Recursion
Mastering Regular Expressions - Jeffrey E.F. Friedl 1 2 3 4


Regular expressions are the wrong tool for the job because you are dealing with nested structures, i.e. recursion.
But there is a simple algorithm to do this, which I described in more detail in this answer to a previous question. The gist is to write code which scans through the string keeping a counter of the open parentheses which have not yet been matched by a closing parenthesis. When that counter returns to zero, then you know you've reached the final closing parenthesis.


You can use regex recursion:
\(([^()]|(?R))*\)


[^\(]*(\(.*\))[^\)]*
[^\(]* matches everything that isn't an opening bracket at the beginning of the string, (\(.*\)) captures the required substring enclosed in brackets, and [^\)]* matches everything that isn't a closing bracket at the end of the string. Note that this expression does not attempt to match brackets; a simple parser (see dehmann's answer) would be more suitable for that.


This answer explains the theoretical limitation of why regular expressions are not the right tool for this task.
Regular expressions can not do this.
Regular expressions are based on a computing model known as Finite State Automata (FSA). As the name indicates, a FSA can remember only the current state, it has no information about the previous states.
In the above diagram, S1 and S2 are two states where S1 is the starting and final step. So if we try with the string 0110 , the transition goes as follows:
0 1 1 0
-> S1 -> S2 -> S2 -> S2 ->S1
In the above steps, when we are at second S2 i.e. after parsing 01 of 0110, the FSA has no information about the previous 0 in 01 as it can only remember the current state and the next input symbol.
In the above problem, we need to know the no of opening parenthesis; this means it has to be stored at some place. But since FSAs can not do that, a regular expression can not be written.
However, an algorithm can be written to do this task. Algorithms are generally falls under Pushdown Automata (PDA). PDA is one level above of FSA. PDA has an additional stack to store some additional information. PDAs can be used to solve the above problem, because we can 'push' the opening parenthesis in the stack and 'pop' them once we encounter a closing parenthesis. If at the end, stack is empty, then opening parenthesis and closing parenthesis matches. Otherwise not.


(?<=\().*(?=\))
If you want to select text between two matching parentheses, you are out of luck with regular expressions. This is impossible(*).
This regex just returns the text between the first opening and the last closing parentheses in your string.
(*) Unless your regex engine has features like balancing groups or recursion. The number of engines that support such features is slowly growing, but they are still not a commonly available.


It is actually possible to do it using .NET regular expressions, but it is not trivial, so read carefully.
You can read a nice article here. You also may need to read up on .NET regular expressions. You can start reading here.
Angle brackets <> were used because they do not require escaping.
The regular expression looks like this:
<
[^<>]*
(
(
(?<Open><)
[^<>]*
)+
(
(?<Close-Open>>)
[^<>]*
)+
)*
(?(Open)(?!))
>


I was also stuck in this situation when dealing with nested patterns and regular-expressions is the right tool to solve such problems.
/(\((?>[^()]+|(?1))*\))/


This is the definitive regex:
\(
(?<arguments>
(
([^\(\)']*) |
(\([^\(\)']*\)) |
'(.*?)'
)*
)
\)
Example:
input: ( arg1, arg2, arg3, (arg4), '(pip' )
output: arg1, arg2, arg3, (arg4), '(pip'
note that the '(pip' is correctly managed as string.
(tried in regulator: http://sourceforge.net/projects/regulator/)


I have written a little JavaScript library called balanced to help with this task. You can accomplish this by doing
balanced.matches({
source: source,
open: '(',
close: ')'
});
You can even do replacements:
balanced.replacements({
source: source,
open: '(',
close: ')',
replace: function (source, head, tail) {
return head + source + tail;
}
});
Here's a more complex and interactive example JSFiddle.


Adding to bobble bubble's answer, there are other regex flavors where recursive constructs are supported.
Lua
Use %b() (%b{} / %b[] for curly braces / square brackets):
for s in string.gmatch("Extract (a(b)c) and ((d)f(g))", "%b()") do print(s) end (see demo)
Raku (former Perl6):
Non-overlapping multiple balanced parentheses matches:
my regex paren_any { '(' ~ ')' [ <-[()]>+ || <&paren_any> ]* }
say "Extract (a(b)c) and ((d)f(g))" ~~ m:g/<&paren_any>/;
# => (｢(a(b)c)｣ ｢((d)f(g))｣)
Overlapping multiple balanced parentheses matches:
say "Extract (a(b)c) and ((d)f(g))" ~~ m:ov:g/<&paren_any>/;
# => (｢(a(b)c)｣ ｢(b)｣ ｢((d)f(g))｣ ｢(d)｣ ｢(g)｣)
See demo.
Python re non-regex solution
See poke's answer for How to get an expression between balanced parentheses.
Java customizable non-regex solution
Here is a customizable solution allowing single character literal delimiters in Java:
public static List<String> getBalancedSubstrings(String s, Character markStart,
Character markEnd, Boolean includeMarkers)
{
List<String> subTreeList = new ArrayList<String>();
int level = 0;
int lastOpenDelimiter = -1;
for (int i = 0; i < s.length(); i++) {
char c = s.charAt(i);
if (c == markStart) {
level++;
if (level == 1) {
lastOpenDelimiter = (includeMarkers ? i : i + 1);
}
}
else if (c == markEnd) {
if (level == 1) {
subTreeList.add(s.substring(lastOpenDelimiter, (includeMarkers ? i + 1 : i)));
}
if (level > 0) level--;
}
}
return subTreeList;
}
}
Sample usage:
String s = "some text(text here(possible text)text(possible text(more text)))end text";
List<String> balanced = getBalancedSubstrings(s, '(', ')', true);
System.out.println("Balanced substrings:\n" + balanced);
// => [(text here(possible text)text(possible text(more text)))]


The regular expression using Ruby (version 1.9.3 or above):
/(?<match>\((?:\g<match>|[^()]++)*\))/
Demo on rubular


The answer depends on whether you need to match matching sets of brackets, or merely the first open to the last close in the input text.
If you need to match matching nested brackets, then you need something more than regular expressions. - see #dehmann
If it's just first open to last close see #Zach
Decide what you want to happen with:
abc ( 123 ( foobar ) def ) xyz ) ghij
You need to decide what your code needs to match in this case.


"""
Here is a simple python program showing how to use regular
expressions to write a paren-matching recursive parser.
This parser recognises items enclosed by parens, brackets,
braces and <> symbols, but is adaptable to any set of
open/close patterns. This is where the re package greatly
assists in parsing.
"""
import re
# The pattern below recognises a sequence consisting of:
# 1. Any characters not in the set of open/close strings.
# 2. One of the open/close strings.
# 3. The remainder of the string.
#
# There is no reason the opening pattern can't be the
# same as the closing pattern, so quoted strings can
# be included. However quotes are not ignored inside
# quotes. More logic is needed for that....
pat = re.compile("""
( .*? )
( \( | \) | \[ | \] | \{ | \} | \< | \> |
\' | \" | BEGIN | END | $ )
( .* )
""", re.X)
# The keys to the dictionary below are the opening strings,
# and the values are the corresponding closing strings.
# For example "(" is an opening string and ")" is its
# closing string.
matching = { "(" : ")",
"[" : "]",
"{" : "}",
"<" : ">",
'"' : '"',
"'" : "'",
"BEGIN" : "END" }
# The procedure below matches string s and returns a
# recursive list matching the nesting of the open/close
# patterns in s.
def matchnested(s, term=""):
lst = []
while True:
m = pat.match(s)
if m.group(1) != "":
lst.append(m.group(1))
if m.group(2) == term:
return lst, m.group(3)
if m.group(2) in matching:
item, s = matchnested(m.group(3), matching[m.group(2)])
lst.append(m.group(2))
lst.append(item)
lst.append(matching[m.group(2)])
else:
raise ValueError("After <<%s %s>> expected %s not %s" %
(lst, s, term, m.group(2)))
# Unit test.
if __name__ == "__main__":
for s in ("simple string",
""" "double quote" """,
""" 'single quote' """,
"one'two'three'four'five'six'seven",
"one(two(three(four)five)six)seven",
"one(two(three)four)five(six(seven)eight)nine",
"one(two)three[four]five{six}seven<eight>nine",
"one(two[three{four<five>six}seven]eight)nine",
"oneBEGINtwo(threeBEGINfourENDfive)sixENDseven",
"ERROR testing ((( mismatched ))] parens"):
print "\ninput", s
try:
lst, s = matchnested(s)
print "output", lst
except ValueError as e:
print str(e)
print "done"


You need the first and last parentheses. Use something like this:
str.indexOf('('); - it will give you first occurrence
str.lastIndexOf(')'); - last one
So you need a string between,
String searchedString = str.substring(str1.indexOf('('),str1.lastIndexOf(')');


because js regex doesn't support recursive match, i can't make balanced parentheses matching work.
so this is a simple javascript for loop version that make "method(arg)" string into array
push(number) map(test(a(a()))) bass(wow, abc)
$$(groups) filter({ type: 'ORGANIZATION', isDisabled: { $ne: true } }) pickBy(_id, type) map(test()) as(groups)
const parser = str => {
let ops = []
let method, arg
let isMethod = true
let open = []
for (const char of str) {
// skip whitespace
if (char === ' ') continue
// append method or arg string
if (char !== '(' && char !== ')') {
if (isMethod) {
(method ? (method += char) : (method = char))
} else {
(arg ? (arg += char) : (arg = char))
}
}
if (char === '(') {
// nested parenthesis should be a part of arg
if (!isMethod) arg += char
isMethod = false
open.push(char)
} else if (char === ')') {
open.pop()
// check end of arg
if (open.length < 1) {
isMethod = true
ops.push({ method, arg })
method = arg = undefined
} else {
arg += char
}
}
}
return ops
}
// const test = parser(`$$(groups) filter({ type: 'ORGANIZATION', isDisabled: { $ne: true } }) pickBy(_id, type) map(test()) as(groups)`)
const test = parser(`push(number) map(test(a(a()))) bass(wow, abc)`)
console.log(test)
the result is like
[ { method: 'push', arg: 'number' },
{ method: 'map', arg: 'test(a(a()))' },
{ method: 'bass', arg: 'wow,abc' } ]
[ { method: '$$', arg: 'groups' },
{ method: 'filter',
arg: '{type:\'ORGANIZATION\',isDisabled:{$ne:true}}' },
{ method: 'pickBy', arg: '_id,type' },
{ method: 'map', arg: 'test()' },
{ method: 'as', arg: 'groups' } ]


While so many answers mention this in some form by saying that regex does not support recursive matching and so on, the primary reason for this lies in the roots of the Theory of Computation.
Language of the form {a^nb^n | n>=0} is not regular. Regex can only match things that form part of the regular set of languages.
Read more # here


I didn't use regex since it is difficult to deal with nested code. So this snippet should be able to allow you to grab sections of code with balanced brackets:
def extract_code(data):
""" returns an array of code snippets from a string (data)"""
start_pos = None
end_pos = None
count_open = 0
count_close = 0
code_snippets = []
for i,v in enumerate(data):
if v =='{':
count_open+=1
if not start_pos:
start_pos= i
if v=='}':
count_close +=1
if count_open == count_close and not end_pos:
end_pos = i+1
if start_pos and end_pos:
code_snippets.append((start_pos,end_pos))
start_pos = None
end_pos = None
return code_snippets
I used this to extract code snippets from a text file.


This do not fully address the OP question but I though it may be useful to some coming here to search for nested structure regexp:
Parse parmeters from function string (with nested structures) in javascript
Match structures like:
matches brackets, square brackets, parentheses, single and double quotes
Here you can see generated regexp in action
/**
* get param content of function string.
* only params string should be provided without parentheses
* WORK even if some/all params are not set
* #return [param1, param2, param3]
*/
exports.getParamsSAFE = (str, nbParams = 3) => {
const nextParamReg = /^\s*((?:(?:['"([{](?:[^'"()[\]{}]*?|['"([{](?:[^'"()[\]{}]*?|['"([{][^'"()[\]{}]*?['")}\]])*?['")}\]])*?['")}\]])|[^,])*?)\s*(?:,|$)/;
const params = [];
while (str.length) { // this is to avoid a BIG performance issue in javascript regexp engine
str = str.replace(nextParamReg, (full, p1) => {
params.push(p1);
return '';
});
}
return params;
};


This might help to match balanced parenthesis.
\s*\w+[(][^+]*[)]\s*


This one also worked
re.findall(r'\(.+\)', s)

Related

Spliting string of arithmetic operations in lua

The following is string of arithmetic operations in lua.
local str ='x+abc*def+y^z+10'
Can this string be splitted so that individual variables or numbers will appear? For example, say string str is splitted into table s. Then the output will be
s[1] = x
s[2] = abc
s[3] = def
s[4] = y
s[5] = z
s[6] = 10
The splitting is to be done with operators +,-,*,\,^,%

Try also this simpler pattern:
local str ='x+(abc*def)+y^z+10'
for w in str:gmatch("%w+") do
print(w)
end

You can use string.gmatch to iterate over your string.
Feel free to add other operators to the pattern.
Refer to https://www.lua.org/manual/5.3/manual.html#6.4.1
local str ='x+abc*def+y^z+10'
local s = {}
for operand in str:gmatch('[^%+%*%^]+') do
table.insert(s, operand)
end

You can use string.gmatch to do what your looking for. you would use the pattern %+%-%*%^/
local str ='x+abc*def+y^z+10'
local s = {}
for value in str:gmatch("[%+%-%*%^/]*(%w*)[%+%-%*%^/]*") do
s[#s + 1] = value
end
print(unpack(s))
Also not that if you need \ as operator as shown in your question it would need to be escaped using an additional \.
Resourse for leaning more about lua patterns: understanding_lua_patterns

parsing nested structures in R

I have a json-like string that represents a nested structure. it is not a real json in that the names and values are not quoted. I want to parse it to a nested structure, e.g. list of lists.
#example:
x_string = "{a=1, b=2, c=[1,2,3], d={e=something}}"
and the result should be like this:
x_list = list(a=1,b=2,c=c(1,2,3),d=list(e="something"))
is there any convenient function that I don't know that does this kind of parsing?
Thanks.

If all of your data is consistent, there is a simple solution involving regex and jsonlite package. The code is:
if(!require(jsonlite, quiet=TRUE)){
#if library is not installed: installs it and loads it into the R session for use.
install.packages("jsonlite",repos="https://ftp.heanet.ie/mirrors/cran.r-project.org")
library(jsonlite)
}
x_string = "{a=1, b=2, c=[1,2,3], d={e=something}}"
json_x_string = "{\"a\":1, \"b\":2, \"c\":[1,2,3], \"d\":{\"e\":\"something\"}}"
fromJSON(json_x_string)
s <- gsub( "([A-Za-z]+)", "\"\\1\"", gsub( "([A-Za-z]*)=", "\\1:", x_string ) )
fromJSON( s )
The first section checks if the package is installed. If it is it loads it, otherwise it installs it and then loads it. I usually include this in any R code I'm writing to make it simpler to transfer between pcs/people.
Your string is x_string, we want it to look like json_x_string which gives the desired output when we call fromJSON().
The regex is split into two parts because it's been a while - I'm pretty sure this could be made more elegant. Then again, this depends on if your data is consistent so I'll leave it like this for now. First it changes "=" to ":", then it adds quotation marks around all groups of letters. Calling fromJSON(s) gives the output:
fromJSON(s)
$a
[1] 1
$b
[1] 2
$c
[1] 1 2 3
$d
$d$e
[1] "something"

I would rather avoid using JSON's parsing for the lack of extendibility and flexibility, and stick to a solution of regex + recursion.
And here is an extendable base code that parses your input string as desired
The main recursion function:
# Parse string
parse.string = function(.string){
regex = "^((.*)=)??\\{(.*)\\}"
# Recursion termination: element parsing
if(iselement(.string)){
return(parse.element(.string))
}
# Extract components
elements.str = gsub(regex, "\\3", .string)
elements.vector = get.subelements(elements.str)
# Recursively parse each element
parsed.elements = list(sapply(elements.vector, parse.string, USE.NAMES = F))
# Extract list's name and return
name = gsub(regex, "\\2", .string)
names(parsed.elements) = name
return(parsed.elements)
}
.
Helping functions:
library(stringr)
# Test if the string is a base element
iselement = function(.string){
grepl("^[^[:punct:]]+=[^\\{\\}]+$", .string)
}
# Parse element
parse.element = function(element.string){
splits = strsplit(element.string, "=")[[1]]
element = splits[2]
# Parse numeric elements
if(!is.na(as.numeric(element))){
element = as.numeric(element)
}
# TODO: Extend here to include vectors
# Reformat and return
element = list(element)
names(element) = splits[1]
return(element)
}
# Get subelements from a string
get.subelements = function(.string){
# Regex of allowed elements - Extend here to include more types
elements.regex = c("[^, ]+?=\\{.+?\\}", #Sublist
"[^, ]+?=\\[.+?\\]", #Vector
"[^, ]+?=[^=,]+") #Base element
str_extract_all(.string, pattern = paste(elements.regex, collapse = "|"))[[1]]
}
.
Parsing results:
string = "{a=1, b=2, c=[1,2,3], d={e=something}}"
string_2 = "{a=1, b=2, c=[1,2,3], d=somthing}"
named_string = "xyz={a=1, b=2, c=[1,2,3], d={e=something, f=22}}"
named_string_2 = "xyz={d={e=something, f=22}}"
parse.string(string)
# [[1]]
# [[1]]$a
# [1] 1
#
# [[1]]$b
# [1] 2
#
# [[1]]$c
# [1] "[1,2,3]"
#
# [[1]]$d
# [[1]]$d$e
# [1] "something"

Convert bitstring to tuple

I'm trying to find out how to convert an Erlang bitstring to a tuple, but so far without any luck.
What I want is to get from for example <<"{1,2}">> the tuple {1,2}.

You can use the modules erl_scan and erl_parse, as in this answer. Since erl_scan:string requires a string, not a binary, you have to convert the value with binary_to_list first:
> {ok, Scanned, _} = erl_scan:string(binary_to_list(<<"{1,2}">>)).
{ok,[{'{',1},{integer,1,1},{',',1},{integer,1,2},{'}',1}],1}
Then, you'd use erl_parse:parse_term to get the actual term. However, this function expects the term to end with a dot, so we have to add it explicitly:
> {ok, Parsed} = erl_parse:parse_term(Scanned ++ [{dot,0}]).
{ok,{1,2}}
Now the variable Parsed contains the result:
> Parsed.
{1,2}

You can use binary functions and erlang:list_to_tuple/1
1> B = <<"{1,2}">>.
<<"{1,2}">>
2> list_to_tuple([list_to_integer(binary_to_list(X)) || X <- binary:split(binary:part(B, 1, byte_size(B)-2), <<",">>, [global])]).
{1,2}

tail() function in XQuery

Is there a way in XQuery to do something like a tail() function?
What I'm trying to accomplish is to get the contents of a file (using "xdmp:filesystem-file($path)") and then display only the last 100 lines. I can't seem to find a good way to do this. Any ideas?
Thank you.

In plain XQuery, this can be accomplished by splitting into lines and getting the desired number of lines from the end of the sequence, then rejoining them, if necessary, i.e.
declare function local:tail($content as xs:string, $number as xs:integer)
{
let $linefeed := "
"
let $lines := tokenize($content, $linefeed)
let $tail := $lines[position() > last() - $number]
return string-join($tail, $linefeed)
};

A pure and short XPath 2.0 solution -- can be used not only in XQuery but in XSLT or in any other PL hosting XPath 2.0:
for $numLines in count(tokenize(., '
'))
return
tokenize(., '
')[position() gt $numLines -100]
Or:
for $numLines in count(tokenize(., '
'))
return
subsequence(tokenize(., '
'), $numLines -100 +1)

if your xdmp:file-xx is a nature of text file then you could use something like
let $f := 'any file system path'
return fn:tokenize(xdmp:filesystem-file($f), '[\n\r]+')[ fn:last() - 2 to fn:last()]
here
i have used newline & carriage return as my token splitter. if you need something else to tokenize u could. but simple log file tailing then this solution works fine.
given example tails last 2 lines of a given file. if you want more than alter fn:last()-2 to fn:last() - x

Split a string ignoring quoted sections

Given a string like this:
a,"string, with",various,"values, and some",quoted
What is a good algorithm to split this based on commas while ignoring the commas inside the quoted sections?
The output should be an array:
[ "a", "string, with", "various", "values, and some", "quoted" ]

Looks like you've got some good answers here.
For those of you looking to handle your own CSV file parsing, heed the advice from the experts and Don't roll your own CSV parser.
Your first thought is, "I need to handle commas inside of quotes."
Your next thought will be, "Oh, crap, I need to handle quotes inside of quotes. Escaped quotes. Double quotes. Single quotes..."
It's a road to madness. Don't write your own. Find a library with an extensive unit test coverage that hits all the hard parts and has gone through hell for you. For .NET, use the free FileHelpers library.

Python:
import csv
reader = csv.reader(open("some.csv"))
for row in reader:
print row

If my language of choice didn't offer a way to do this without thinking then I would initially consider two options as the easy way out:
Pre-parse and replace the commas within the string with another control character then split them, followed by a post-parse on the array to replace the control character used previously with the commas.
Alternatively split them on the commas then post-parse the resulting array into another array checking for leading quotes on each array entry and concatenating the entries until I reached a terminating quote.
These are hacks however, and if this is a pure 'mental' exercise then I suspect they will prove unhelpful. If this is a real world problem then it would help to know the language so that we could offer some specific advice.

Of course using a CSV parser is better but just for the fun of it you could:
Loop on the string letter by letter.
If current_letter == quote :
toggle inside_quote variable.
Else if (current_letter ==comma and not inside_quote) :
push current_word into array and clear current_word.
Else
append the current_letter to current_word
When the loop is done push the current_word into array

The author here dropped in a blob of C# code that handles the scenario you're having a problem with:
CSV File Imports in .Net
Shouldn't be too difficult to translate.

What if an odd number of quotes appear
in the original string?
This looks uncannily like CSV parsing, which has some peculiarities to handling quoted fields. The field is only escaped if the field is delimited with double quotations, so:
field1, "field2, field3", field4, "field5, field6" field7
becomes
field1
field2, field3
field4
"field5
field6" field7
Notice if it doesn't both start and end with a quotation, then it's not a quoted field and the double quotes are simply treated as double quotes.
Insedently my code that someone linked to doesn't actually handle this correctly, if I recall correctly.

Here's a simple python implementation based on Pat's pseudocode:
def splitIgnoringSingleQuote(string, split_char, remove_quotes=False):
string_split = []
current_word = ""
inside_quote = False
for letter in string:
if letter == "'":
if not remove_quotes:
current_word += letter
if inside_quote:
inside_quote = False
else:
inside_quote = True
elif letter == split_char and not inside_quote:
string_split.append(current_word)
current_word = ""
else:
current_word += letter
string_split.append(current_word)
return string_split

I use this to parse strings, not sure if it helps here; but with some minor modifications perhaps?
function getstringbetween($string, $start, $end){
$string = " ".$string;
$ini = strpos($string,$start);
if ($ini == 0) return "";
$ini += strlen($start);
$len = strpos($string,$end,$ini) - $ini;
return substr($string,$ini,$len);
}
$fullstring = "this is my [tag]dog[/tag]";
$parsed = getstringbetween($fullstring, "[tag]", "[/tag]");
echo $parsed; // (result = dog)
/mp

This is a standard CSV-style parse. A lot of people try to do this with regular expressions. You can get to about 90% with regexes, but you really need a real CSV parser to do it properly. I found a fast, excellent C# CSV parser on CodeProject a few months ago that I highly recommend!

Here's one in pseudocode (a.k.a. Python) in one pass :-P
def parsecsv(instr):
i = 0
j = 0
outstrs = []
# i is fixed until a match occurs, then it advances
# up to j. j inches forward each time through:
while i < len(instr):
if j < len(instr) and instr[j] == '"':
# skip the opening quote...
j += 1
# then iterate until we find a closing quote.
while instr[j] != '"':
j += 1
if j == len(instr):
raise Exception("Unmatched double quote at end of input.")
if j == len(instr) or instr[j] == ',':
s = instr[i:j] # get the substring we've found
s = s.strip() # remove extra whitespace
# remove surrounding quotes if they're there
if len(s) > 2 and s[0] == '"' and s[-1] == '"':
s = s[1:-1]
# add it to the result
outstrs.append(s)
# skip over the comma, move i up (to where
# j will be at the end of the iteration)
i = j+1
j = j+1
return outstrs
def testcase(instr, expected):
outstr = parsecsv(instr)
print outstr
assert expected == outstr
# Doesn't handle things like '1, 2, "a, b, c" d, 2' or
# escaped quotes, but those can be added pretty easily.
testcase('a, b, "1, 2, 3", c', ['a', 'b', '1, 2, 3', 'c'])
testcase('a,b,"1, 2, 3" , c', ['a', 'b', '1, 2, 3', 'c'])
# odd number of quotes gives a "unmatched quote" exception
#testcase('a,b,"1, 2, 3" , "c', ['a', 'b', '1, 2, 3', 'c'])

Here's a simple algorithm:
Determine if the string begins with a '"' character
Split the string into an array delimited by the '"' character.
Mark the quoted commas with a placeholder #COMMA#
If the input starts with a '"', mark those items in the array where the index % 2 == 0
Otherwise mark those items in the array where the index % 2 == 1
Concatenate the items in the array to form a modified input string.
Split the string into an array delimited by the ',' character.
Replace all instances in the array of #COMMA# placeholders with the ',' character.
The array is your output.
Heres the python implementation:
(fixed to handle '"a,b",c,"d,e,f,h","i,j,k"')
def parse_input(input):
quote_mod = int(not input.startswith('"'))
input = input.split('"')
for item in input:
if item == '':
input.remove(item)
for i in range(len(input)):
if i % 2 == quoted_mod:
input[i] = input[i].replace(",", "#COMMA#")
input = "".join(input).split(",")
for item in input:
if item == '':
input.remove(item)
for i in range(len(input)):
input[i] = input[i].replace("#COMMA#", ",")
return input
# parse_input('a,"string, with",various,"values, and some",quoted')
# -> ['a,string', ' with,various,values', ' and some,quoted']
# parse_input('"a,b",c,"d,e,f,h","i,j,k"')
# -> ['a,b', 'c', 'd,e,f,h', 'i,j,k']

I just couldn't resist to see if I could make it work in a Python one-liner:
arr = [i.replace("|", ",") for i in re.sub('"([^"]*)\,([^"]*)"',"\g<1>|\g<2>", str_to_test).split(",")]
Returns ['a', 'string, with', 'various', 'values, and some', 'quoted']
It works by first replacing the ',' inside quotes to another separator (|),
splitting the string on ',' and replacing the | separator again.

Since you said language agnostic, I wrote my algorithm in the language that's closest to pseudocode as posible:
def find_character_indices(s, ch):
return [i for i, ltr in enumerate(s) if ltr == ch]
def split_text_preserving_quotes(content, include_quotes=False):
quote_indices = find_character_indices(content, '"')
output = content[:quote_indices[0]].split()
for i in range(1, len(quote_indices)):
if i % 2 == 1: # end of quoted sequence
start = quote_indices[i - 1]
end = quote_indices[i] + 1
output.extend([content[start:end]])
else:
start = quote_indices[i - 1] + 1
end = quote_indices[i]
split_section = content[start:end].split()
output.extend(split_section)
output += content[quote_indices[-1] + 1:].split()
return output