REGEXP_REPLACE replace spaces between two symbols - postgresql

Question

I need to replace all spaces with one % between two specific symbols (# and &); like followings:
'this # is test &that did not #turn& out well'
should be converted to
'this #%is%test%&that did not #turn& out well'
and
'#pattern matching& is my number one enemy'
to
'#pattern%matching& is my number one enemy'
I almost read all related questions in stackoverflow and other sites but couldn't get a helpful answer.

Answer 1

One (inefficient) way of doing this is by doing multiple REGEXP_REPLACE calls.
For example, lets look at the following plpgsql function.
CREATE OR REPLACE FUNCTION replaceSpacesBetweenTwoSymbols(startChar TEXT, endChar TEXT, textToParse TEXT)
RETURNS TEXT
AS $$
DECLARE resultText TEXT := textToParse;
DECLARE tempText TEXT := textToParse;
BEGIN
WHILE TRUE LOOP
tempText = REGEXP_REPLACE(resultText,
'(' || startChar || '[^' || endChar || ']*)' || '( )(.*' || endChar || ')',
'\1%\3');
IF tempText = resultText
THEN RETURN resultText;
END IF;
resultText := tempText;
END LOOP;
RETURN resultText;
END;
$$
LANGUAGE 'plpgsql';
We create a function that takes three arguments, the startChar, the endChar and the textToParse which holds the text that will be trimmed.
We start by creating a a regular expression based on the startChar and endChar. If the value of startChar is # and the value of endChar is & we will get the following regular expression:
(#[^&]*)( )(.*&)
This regular expression is consisted of three groups:
(#[^&]*) - This group matches the text that is between the # and an an empty space character - ' ';
( ) - This group matches a single space character.
(.*&) - This group matches the text that is between a space character and the & character.
In order to replace the space (group 2), we use the following REGEXP_REPLACE call:
REGEXP_REPLACE(resultText,' (#[^&]*)( )(.*&)', '\1%\3')
From that expression you can see that we are replacing the second group (which is a space) with the % character.
This way, we will only replace one space per one REGEXP_REPLACE execution.
Once we find that there are no more spaces that need to be replaced, we return the modified TEXT.
At this moment, the spaces are replaced with % characters. One last thing we need to do is to replace the multiple consecutive % characters with a single %.
That can be done with another REGEXP_REPLACE call at the end.
So for example:
SELECT REGEXP_REPLACE(replaceSpacesBetweenTwoSymbols('#','&','this # is test &that did not #turn& out well'),'%{2,}','%');
Will return
this #%is%test%&that did not #turn& out well
as a result, while this
SELECT REGEXP_REPLACE(replaceSpacesBetweenTwoSymbols('#','&','this is #a more complex& task #test a a & w'),'%{2,}','%');
will return
this is #a%more%complex& task #test%a%a%& w
as a result.