Format string using Regular Expression

Question

Input string output format...
SELECT q'<select ab_c "ABC", efg "EFG" from dual>' str FROM DUAL
Output:
STR                                 
select ab_c "ABC", efg "EFG" from dual
Required output format using regular expression...
STR                                 
select 'ab_c' "ABC", 'efg' "EFG" from dual

Answer 1

Regular expressions have many limitations as parsing tools, and you didn't specify the rules you wanted. This expression puts quotes around the non blank string before a quoted string:
SELECT regexp_replace(q'<select ab_c "ABC", efg "EFG" from dual>',
                      '([^" ]+)( +"[^ ]*")' , '''\1''\2' ) str FROM DUAL;
STR
select 'ab_c' "ABC", 'efg' "EFG" from dual
{code}
It is not robust - a missing " will confuse it, and you should be using bind variables anyway.