In a file I have following set of data
FX_DETAIL_69#chf4
FX_DETAIL_75#chf1
FX_DETAIL_07#bluXCFG#chf2
FX_DETAIL_99#bluXCFG#chf9
FX_DETAIL_62#chf6
I have written the following regular expression in Python:
FX_DETAIL\_(\d+)\#(\w+)
How can I use the optional option to exclude value .bluXCFG?
You can use a greedy wildcard (.*) to consume everything until the last #(\w+):
FX_DETAIL_(\d+).*#(\w+)
Use (?:#bluXCFG)? to specify an optional group.
FX_DETAIL_(\d+)(?:#bluXCFG)?#(\w+)
BTW, there's no need to escape _ and #, they have no special meaning.
You could optionally match all that follows except a newline or the # itself till the next occurrence of # using a negated character class.
FX_DETAIL_(\d+)#(?:[^#\r\n]*#)?(\w+)