Re^3: Regex with condition

[AnomalousMonk]

In my reply above, I wrote

However, also note that if the "random amount of other text" preceding the  'b' in a trigger line may contain any whitespace, then the
    my $pre = qr{ \S+ \s }xms;
regex will have to be changed accordingly.

In the OP, a typical  'b' line was
    '1n5P/1P4PK/1q6 b - - 2 42"]'
In the post to which this is a reply, a typical  'b' line is
    '[FEN "1B6/1Q4bk/R5p1/1pp4p/8/1n5P/1P4PK/1q6 b - - 2 42"]'
with more than one whitespace character before the 'b'. Accordingly, I have altered the $pre regex to
    my $pre  = qr{ \S+ \s \S+ \s }xms;
(This is not what I would consider a "robust" regex, but you will have to provide a regex that best matches your data if you wish an improvement.)

In addition, in the OP a typical  'Weiss' line had leading whitespace; in the most recent post, it has none. Accordingly, I have altered the $post regex to
    my $post = qr{ \s [^\n]+ \n [^\{]* \{ }xms;
(note [^\{]* vice [^\{]+).

I have downloaded your latest data to my file 1148125.dat. With the changes above and your latest data:

c:\@Work\Perl\monks\OldChamp>perl -wMstrict -e
"use 5.010;
 ;;
 my $t = do { local $/;  <>; };
 print qq{[[$t]] \n\n};
 ;;
 my $pre  = qr{ \S+ \s \S+ \s }xms;
 my $post = qr{ \s [^\n]+ \n [^\{]* \{ }xms;
 ;;
 $t =~ s{ ^ $pre b $post \K Weiss \b }
        {Schwarz}xmsg;
 ;;
 print qq{<<$t>> \n\n};
"  1148125.dat
[[..........
[FEN "1B3k2/2R1b3/4p1pp/2r1P1p1/6P1/7P/5PK1/8 w - - 4 34"]
{Weiss am Zug}  *

..........
[FEN "1B6/1Q4bk/R5p1/1pp4p/8/1n5P/1P4PK/1q6 b - - 2 42"]
{Weiss am Zug}  *

...........
[FEN "1Bn4r/1k3q2/1pp1bbp1/1N1p1p1r/Q2Pp3/6PN/PP2PPB1/K1R4R b - - 0 23
+"]
{Weiss am Zug}  *

...........
[FEN "1K6/4kp2/1P4p1/7p/7P/1r3PP1/1p6/1R6 w - - 3 52"]
{Weiss am Zug}  *

]]

<<..........
[FEN "1B3k2/2R1b3/4p1pp/2r1P1p1/6P1/7P/5PK1/8 w - - 4 34"]
{Weiss am Zug}  *

..........
[FEN "1B6/1Q4bk/R5p1/1pp4p/8/1n5P/1P4PK/1q6 b - - 2 42"]
{Schwarz am Zug}  *

...........
[FEN "1Bn4r/1k3q2/1pp1bbp1/1N1p1p1r/Q2Pp3/6PN/PP2PPB1/K1R4R b - - 0 23
+"]
{Schwarz am Zug}  *

...........
[FEN "1K6/4kp2/1P4p1/7p/7P/1r3PP1/1p6/1R6 w - - 3 52"]
{Weiss am Zug}  *

>>

At last,  Weiss has changed.

[OldChamp]

Dear AnomalousMonk, one thing is for sure, you are obviously the most helpful Monk in this forum with a great heart and a lot of patience with someone like me, who makes one mistake after the other. I have studied your replies, but I had difficulties in understanding the real meaning of $pre and also the $post, partly because this new form of writing a regex is new for me, in the book I have read about regex, this form with the modifier x (which is clearly more readable then the old form) was not used. Also the use of { instead of / was at first glance a little confusing for me. As you wisely have stated, I should have tried harder to learn fishing and not only to consume a fish. In my OP I have abreviated my data so to make my question short, not understanding that this changed the problem.

Concerning the space in the $pre, I have just overlooked the space betweeen FEN and the ". Concerning the $post, in my real data there is leading whitespace before the 'Weiss' line, but in the testfile I have deleted it, for the same reason as before, I wanted to be short.

After so many mistakes which I have made I have studied your solution more thoroughly and now I think I have understood it. At last, I have learned a little bit to fish. But when you are 72 years old, it's not so easy and I must confess that I have only studied in books the parts, which I think were needed to solve my problems.

Once again, many thanks for your great help

[AnomalousMonk]

... many thanks for your great help

It may or may not have been so great, but you are very welcome in any case.

... you are obviously the most helpful Monk in this forum ...

Many thanks for the compliment, but if you are around this place for long, you will find others who are much more patient and helpful (not to mention authoritative!) than I. In general, the effort the gentle Monks will expend to help you is in direct proportion to the effort you are willing to expend to help yourself.

... I had difficulties in understanding the real meaning of $pre and also the $post ... this new form of writing a regex is new for me ...

I like this approach to composing regexes. The rationale for factoring regexes in this way is the same as for factoring functions into subsidiary functions: they become easier to think about, maintain, etc. And, of course, the free use of whitespace allowed by the  /x switch greatly aids readability.

In my OP I have abreviated my data ... I have just overlooked the space betweeen FEN and the " ... in my real data there is leading whitespace before the 'Weiss' line, but in the testfile I have deleted it ...

I'm sorry if a note of annoyance crept into my responses anent the changing data examples in your posts. These data are instances of "specification by example", and changing a specification, however implicit, after work has been done is always irritating. The design of regexes, parsers, etc., for data handling is very sensitive to the detailed structure of the data. The Devil is in the details, and sometimes the Devil uses these details to tempt us to the deadly sin of Wrath!