I need to parse a string that contains some parentheses disposed recursively, but i'm having trouble with determining priority of parentheses.
For exemple, I have the string
$truth = "((A^¬B)->C)";
and I need to return what is between the parentheses. I've already done it with the following regex:
preg_match_all("~\((.*?)\)~", $truth, $str);
But the problem is that it returns what is between the first "(" and the first ")", which is
(A^¬B
Instead of this, i need it to 'know' where the parentheses closes correctly, in order to return
(A^¬B)->C
How can I return this respecting the priority order? Thanks!
The main problem you have right now is the ? non-greedy bit. If you change that to just .+ greedy it will match what you want.
$truth = "((A^¬B)->C)";
preg_match('/\(.+\)/', $truth, $match);
Try it
Output
(A^¬B)->C
If you want to match the inner pair you can use a recursive subpattern:
$truth = "((A^¬B)->C)";
preg_match('/\(([^()]+|(?0))\)/', $truth, $match);
Try It online
Output
A^¬B
If you need to go further then that you can make a lexer/parser. I have some examples here:
https://github.com/ArtisticPhoenix/MISC/tree/master/Lexers
For your sample string, something like this will recursively give you the contents of the parentheses. It works by forcing the parentheses matched to be the outermost pair by using ^[^(]* and [^)]*$ at each end of the regex.
$truth = "((A^¬B)->C)";
while (strpos($truth, '(') !== false) {
preg_match("~^[^(]*\((.*?)\)[^)]*$~", $truth, $str);
$truth = $str[1];
echo "$truth\n";
}
Output
(A^¬B)->C
A^¬B
Note however this will not correctly parse a string such as (A+B)-(C+D). If that could be your scenario, this answer might help.
Demo on 3v4l.org
Related
I am using preg_match() to extract pieces of text from a variable, and let's say the variable looks like this:
[htmlcode]This is supposed to be displayed[/htmlcode]
middle text
[htmlcode]This is also supposed to be displayed[/htmlcode]
i want to extract the contents of the [htmlcode]'s and input them into an array. i am doing this by using preg_match().
preg_match('/\[htmlcode\]([^\"]*)\[\/htmlcode\]/ms', $text, $matches);
foreach($matches as $value){
return $value . "<br />";
}
The above code outputs
[htmlcode]This is supposed to be displayed[/htmlcode]middle text[htmlcode]This is also supposed to be displayed[/htmlcode]
instead of
[htmlcode]This is supposed to be displayed[/htmlcode]
[htmlcode]This is also supposed to be displayed[/htmlcode]
and if have offically run out of ideas
As explained already; the * pattern is greedy. Another thing is to use preg_match_all() function. It'll return you a multi-dimension array of matched content.
preg_match_all('#\[htmlcode\]([^\"]*?)\[/htmlcode\]#ms', $text, $matches);
foreach( $matches[1] as $value ) {
And you'll get this: http://codepad.viper-7.com/z2GuSd
A * grouper is greedy, i.e. it will eat everything until last [/htmlcode]. Try replacing * with non-greedy *?.
* is by default greedy, ([^\"]*?) (notice the added ?) should make it lazy.
What do lazy and greedy mean in the context of regular expressions?
Look at this piece of code:
preg_match('/\[htmlcode\]([^\"]*)\[\/htmlcode\]/ms', $text, $matches);
foreach($matches as $value){
return $value . "<br />";
}
Now, if your pattern works fine and all is ok, you should know:
return statement will break all loops and will exit the function.
The first element in matches is the whole match, the whole string. In your case $text
So, what you did is returned the first big string and exited the function.
I suggest you can check for desired results:
$matches[1] and $matches[2]
I have string as abvd.qweqw.sdfs.a=aqwrwewrwerrew. I need to parse this string and get piece before = and after =. Symbol . can occur many times. So, please, tell me, which regular expression can I use for parsing? Thank you.
Purely based on your example:
/([a-z.]+)=([a-z]+)/
Edit
But actually:
/([a-z_.]+)=(.*)/i
The results are in memory groups 1 and 2. In code:
if (preg_match('/^([a-z_.]+)=(.*)/i', $str, $matches)) {
// $matches[1] contains part before =
// $matches[2] contains part after =
}
Btw, I've tweaked the expression by anchoring it (using ^). If that doesn't work, just remove it from the expression.
You can use simple string function for that.
list($first, $second) = explode('=', 'abvd.qweqw.sdfs.a=aqwrwewrwerrew);
Thats the full code.
<?php
if(preg_match('/([a-z.]+)=([a-z]+)/', "abvd.qweqw.sdfs.a=aqwrwewrwerrew", $matches)){
print $matches[1]."\n";
print $matches[2]."\n";
}
?>
<?php
$string = "Movies and Stars I., 32. part";
$pattern = "((IX|IV|V?I{0,3}[\.]))";
if(preg_match($pattern, $string, $x) == false)
{
print "NAPAKA!";
}
else
{
print_r($x);
}
?>
And the response is:
Array ( [0] => I. [1] => I. )
I should get only 1 response... Why do I get multiple responses?
The element at index 0 is the whole matched string. The element at index 1 is the contents of the first capture group, i.e. the content inside the parenthesis. In this case, they just happen to be the same. Just use $x[0] to get the value you're looking for.
The nested parenthesis should, in this instance, be a "non-capturing" subpattern.
$pattern = "~((?:IX|IV|V?I{0,3}[\.]))~";
Try that. It will tell the regex compiler to not capture the results of those parenthesis into the array.
In fact, looking at your regex, you don't even need those parenthesis. Make your regex this:
$pattern = "~IX|IV|V?I{0,3}[\.]~";
That should also work.
Your pattern has multiple groups in it -> the () brackets tell you what to capture in your match.
Try this:
$pattern = "(IX|IV|V?I{0,3}[\.])";
If you have a hard time identifying the wanted groups in the result you can name them as specified in the php.net documentation.
That would look something like this:
$pattern = "(?P<groupname>IX|IV|V?I{0,3}[\.])";
You get 0-indexed for all mathced string and result for every paretness (). it's helpful to get groups i.e
preg_match('~([0-9]+)([a-z]+)','12abc',$x);
$x is ([0]=>12abc [1]=>12 [2]=>abc)
In your case you can simply delete () (1 pair ot them, 1 pair is used as delimiters)
Ok this is really difficult to explain in English, so I'll just give an example.
I am going to have strings in the following format:
key-value;key1-value;key2-...
and I need to extract the data to be an array
array('key'=>'value','key1'=>'value1', ... )
I was planning to use regexp to achieve (most of) this functionality, and wrote this regular expression:
/^(\w+)-([^-;]+)(?:;(\w+)-([^-;]+))*;?$/
to work with preg_match and this code:
for ($l = count($matches),$i = 1;$i<$l;$i+=2) {
$parameters[$matches[$i]] = $matches[$i+1];
}
However the regexp obviously returns only 4 backreferences - first and last key-value pairs of the input string. Is there a way around this? I know I can use regex just to test the correctness of the string and use PHP's explode in loops with perfect results, but I'm really curious whether it's possible with regular expressions.
In short, I need to capture an arbitrary number of these key-value; pairs in a string by means of regular expressions.
You can use a lookahead to validate the input while you extract the matches:
/\G(?=(?:\w++-[^;-]++;?)++$)(\w++)-([^;-]++);?/
(?=(?:\w++-[^;-]++;?)++$) is the validation part. If the input is invalid, matching will fail immediately, but the lookahead still gets evaluated every time the regex is applied. In order to keep it (along with the rest of the regex) in sync with the key-value pairs, I used \G to anchor each match to the spot where the previous match ended.
This way, if the lookahead succeeds the first time, it's guaranteed to succeed every subsequent time. Obviously it's not as efficient as it could be, but that probably won't be a problem--only your testing can tell for sure.
If the lookahead fails, preg_match_all() will return zero (false). If it succeeds, the matches will be returned in an array of arrays: one for the full key-value pairs, one for the keys, one for the values.
regex is powerful tool, but sometimes, its not the best approach.
$string = "key-value;key1-value";
$s = explode(";",$string);
foreach($s as $k){
$e = explode("-",$k);
$array[$e[0]]=$e[1];
}
print_r($array);
Use preg_match_all() instead. Maybe something like:
$matches = $parameters = array();
$input = 'key-value;key1-value1;key2-value2;key123-value123;';
preg_match_all("/(\w+)-([^-;]+)/", $input, $matches, PREG_SET_ORDER);
foreach ($matches as $match) {
$parameters[$match[1]] = $match[2];
}
print_r($parameters);
EDIT:
to first validate if the input string conforms to the pattern, then just use:
if (preg_match("/^((\w+)-([^-;]+);)+$/", $input) > 0) {
/* do the preg_match_all stuff */
}
EDIT2: the final semicolon is optional
if (preg_match("/^(\w+-[^-;]+;)*\w+-[^-;]+$/", $input) > 0) {
/* do the preg_match_all stuff */
}
No. Newer matches overwrite older matches. Perhaps the limit argument of explode() would be helpful when exploding.
what about this solution:
$samples = array(
"good" => "key-value;key1-value;key2-value;key5-value;key-value;",
"bad1" => "key-value-value;key1-value;key2-value;key5-value;key-value;",
"bad2" => "key;key1-value;key2-value;key5-value;key-value;",
"bad3" => "k%ey;key1-value;key2-value;key5-value;key-value;"
);
foreach($samples as $name => $value) {
if (preg_match("/^(\w+-\w+;)+$/", $value)) {
printf("'%s' matches\n", $name);
} else {
printf("'%s' not matches\n", $name);
}
}
I don't think you can do both validation and extraction of data with one single regexp, as you need anchors (^ and $) for validation and preg_match_all() for the data, but if you use anchors with preg_match_all() it will only return the last set matched.
those reqular expressions drive me crazy. I'm stuck with this one:
test1:[[link]] test2:[[gold|silver]] test3:[[out1[[inside]]out2]] test4:this|not
Task:
Remove all [[ and ]] and if there is an option split choose the later one so output should be:
test1:link test2:silver test3:out1insideout2 test4:this|not
I came up with (PHP)
$text = preg_replace("/\\[\\[|\\]\\]/",'',$text); // remove [[ or ]]
this works for part1 of the task. but before that I think I should do the option split, my best solution:
$text = preg_replace("/\\[\\[(.*\|)(.*?)\\]\\]/",'$2',$text);
Result:
test1:silver test3:[[out1[[inside]]out2]] this|not
I'm stuck. may someone with some free minutes help me? Thanks!
I think the easiest way to do this would be multiple passes. Use a regular expression like:
\[\[(?:[^\[\]]*\|)?([^\[\]]+)\]\]
This will replace option strings to give you the last option from the group. If you run it repeatedly until it no longer matches, you should get the right result (the first pass will replace [[out1[[inside]]out2]] with [[out1insideout2]] and the second will ditch the brackets.
Edit 1: By way of explanation,
\[\[ # Opening [[
(?: # A non-matching group (we don't want this bit)
[^\[\]] # Non-bracket characters
* # Zero or more of anything but [
\| # A literal '|' character representing the end of the discarded options
)? # This group is optional: if there is only one option, it won't be present
( # The group we're actually interested in ($1)
[^\[\]] # All the non-bracket characters
+ # Must be at least one
) # End of $1
\]\] # End of the grouping.
Edit 2: Changed expression to ignore ']' as well as '[' (it works a bit better like that).
Edit 3: There is no need to know the number of nested brackets as you can do something like:
$oldtext = "";
$newtext = $text;
while ($newtext != $oldtext)
{
$oldtext = $newtext;
$newtext = preg_replace(regexp,replace,$oldtext);
}
$text = $newtext;
Basically, this keeps running the regular expression replace until the output is the same as the input.
Note that I don't know PHP, so there are probably syntax errors in the above.
This is impossible to do in one regular expression since you want to keep content in multiple "hierarchies" of the content. It would be possible otherwise, using a recursive regular expression.
Anyways, here's the simplest, most greedy regular expression I can think of. It should only replace if the content matches your exact requirements.
You will need to escape all backslashes when putting it into a string (\ becomes \\.)
\[\[((?:[^][|]+|(?!\[\[|]])[^|])++\|?)*]]
As others have already explained, you use this with multiple passes. Keep looping while there are matches, performing replacement (only keeping match group 1.)
Difference from other regular expressions here is that it will allow you to have single brackets in the content, without breaking:
test1:[[link]] test2:[[gold|si[lv]er]]
test3:[[out1[[in[si]de]]out2]] test4:this|not
becomes
test1:[[link]] test2:si[lv]er
test3:out1in[si]deout2 test4:this|not
Why try to do it all in one go. Remove the [[]] first and then deal with options, do it in two lines of code.
When trying to get something going favour clarity and simplicity.
Seems like you have all the pieces.
Why not just simply remove any brackets that are left?
$str = 'test1:[[link]] test2:[[gold|silver]] test3:[[out1[[inside]]out2]] test4:this|not';
$str = preg_replace('/\\[\\[(?:[^|\\]]+\\|)+([^\\]]+)\\]\\]/', '$1', $str);
$str = str_replace(array('[', ']'), '', $str);
Well, I didn't stick to just regex, because I'm of a mind that trying to do stuff like this with one big regex leads you to the old joke about "Now you have two problems". However, give something like this a shot:
$str = 'test1:[[link]] test2:[[gold|silver]] test3:[[out1[[inside]]out2]] test4:this|not'; $reg = '/(.*?):(.*?)( |$)/';
preg_match_all($reg, $str, $m);
foreach($m[2] as $pos => $match) {
if (strpos($match, '|') !== FALSE && strpos($match, '[[') !== FALSE ) {
$opt = explode('|', $match); $match = $opt[count($opt)-1];
}
$m[2][$pos] = str_replace(array('[', ']'),'', $match );
}
foreach($m[1] as $k=>$v) $result[$k] = $v.':'.$m[2][$k];
This is C# using only using non-escaped strings, hence you will have to double the backslashes in other languages.
String input = "test1:[[link]] " +
"test2:[[gold|silver]] " +
"test3:[[out1[[inside]]out2]] " +
"test4:this|not";
String step1 = Regex.Replace(input, #"\[\[([^|]+)\|([^\]]+)\]\]", #"[[$2]]");
String step2 = Regex.Replace(step1, #"\[\[|\]\]", String.Empty);
// Prints "test1:silver test3:out1insideout2 test4:this|not"
Console.WriteLine(step2);
$str = 'test1:[[link]] test2:[[gold|silver]] test3:[[out1[[inside]]out2]] test4:this|not';
$s = preg_split("/\s+/",$str);
foreach ($s as $k=>$v){
$v = preg_replace("/\[\[|\]\]/","",$v);
$j = explode(":",$v);
$j[1]=preg_replace("/.*\|/","",$j[1]);
print implode(":",$j)."\n";
}