I can't find out with regex - regex

Question

I'm trying to grab all the chords from a song and place into HTML elements. I'm using this regex
/(\W)(\s)( Chord )\s/
This regex doesn't find all the chords I need. What am I doing wrong?
For example song:
Intro: D G D G D G A G
D G
Klausei ko taip žiūriu
D G
Tavęs ausys neapgavo
D G
Aš kilnų tikslą turiu
D G
Sukišt liežuvį į burną tavo
A G D E G
Tai jokia nepagarba
A D E G
Ir ne kančia
A D E G
Ir ne bėda
A D E G
Greičiau likimo dovana
D D G
Mes pasirengę tegu
Mums gimsta dukros ir arba sūnūs
Arba visi kartu
Ir kuo daugiau, lai mums linksma būna
Tai beveik prabanga
Jokia bėda
Ir ne kančia
Tiesiog likimo dovana

Answer 1

Regex expression works with patterns not with 'knowledgement', I mean, the regex doesn't know really what kind of pattern is a Chorus or a url or whatever.
But you can define a regex with your pattern knowledgement to capture the things that you believe that belong to your pattern.
In this case you want to capture the chords, which appears to be the capital single letters in the range from A-G or de Upper-lower case in the same range followed by letter m.
With spaces by spaces at possibly both sides.
So, you can define this regex:
/(?<=\s)([ABCDEFG]|Am|Bm|Cm|Dm|Em|Gm)(?=\s)/gm
Which means (?<=\s) : look for \spaces at the beginning of the pattern but don't capture them.
Then ([ABCDEFG]|Am|Bm|Cm|Dm|Em|Gm) : look for one letter of the collection [ABC...G] or the combination Am or Bm or...
Then (?=\s) which looks for \spaces at the end of the pattern (without capture them).
https://regex101.com/r/iE1xN3/1
Also you can redefine your regex into this,
/(?<=\s)([A-G]m?)(?=\s)/gm
Which is the same but expressed in other way, where ([A-G]m?): it means, look for a letter in the range of A...G which can be followed by the letter m.
https://regex101.com/r/iE1xN3/2
For javascript (which doesn't support look-behind you can do this:
/(\b)([A-G]m?)(?=\s)/gm
https://regex101.com/r/iE1xN3/3
thanks #stribizhev for the feedback)

Answer 2

I don't know what exactly you want to replace with.
I am using:
\b([A-G])\b
Which means word break, the letters A-G, word break.
https://regex101.com/r/kG0kE5/1
One problem with this method and mayo's answer is if you have lyrics with the word "A" in them.
I would probably write a program that went line by line to determine if the entire line was only chords, and only process those lines.
For example:
A long, long time ago I can still remember how that music used to make me smile .
Most solutions will end up picking "A" in "A long" and recognizing it as a chord.

Answer 3

You can use a regex like this to match the relevan part of a "line" with chords (with multiline m and global g modifiers).
This works selecting sections with one or more "Chords" (reducing the false positive cases):
\b(?:([A-G]m?) *)+$
Try the regex online here
NB: note that the online solution skip correctly a line such as A first letter of the alphabet but as a caveat it matches a trailing A-G (this is an improbable event in lyrics).
In php code:
$re = "/\\b(?:([A-G]m?) *)+$/m";
$str = "Intro: D G D G D G A G\n\nD G\nKlausei ko taip žiūriu\nD G\nTavęs ausys neapgavo\nD G\nAš kilnų tikslą turiu\nD G\nSukišt liežuvį į burną tavo\nA G D E G\nTai jokia nepagarba\nA D E G\nIr ne kančia\nA D E G\nIr ne bėda\nA D E G\nGreičiau likimo dovana\n\nD D G \n\nMes pasirengę tegu\nMums gimsta dukros ir arba sūnūs\nArba visi kartu\nIr kuo daugiau, lai mums linksma būna\n\nTai beveik prabanga\nJokia bėda\nIr ne kančia\nTiesiog likimo dovana";
preg_match_all($re, $str, $matches);
print_r($matches[0]);
Output:
Array
(
[0] => D G D G D G A G
[1] => D G
[2] => D G
[3] => D G
[4] => D G
[5] => A G D E G
[6] => A D E G
[7] => A D E G
[8] => A D E G
[9] => D D G
)