Re^2: matching first paragraph satisfying condition

perl -0pe 's/pattern1|pattern2/$1/gs'; apparently the "or" operator doesn't work as expected here.

The | alternation operator has pretty low precedence, so it kind of depends on what your expectations are :-) A common trap is to write something like /^foo|bar$/ and expect that to match only "foo" or "bar", when in fact it is matching ^foo or bar$ - the correct way to express that would have been /^(foo|bar)$/ or /^(?:foo|bar)$/.

Based on your $1 in the replacement, I suspect you were doing something like s/f(o)o|b(a)r/$1/g and expecting the string "bar" to be turned into "a"? In that case, you need the "branch reset" pattern (?|...) (perlre): s/(?|f(o)o|b(a)r)/$1/g will replace "foo" with "o" and "bar" with "a".

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Re^3: matching first paragraph satisfying condition by mnshptl32 (Initiate) on Aug 20, 2019 at 18:07 UTC
Thank you, haukex, for the information about the correct use of the branch reset, and sorry for making you guess my incorrect code. It was (and is) a bit of a moot point, since I've been given multiple perl solutions to my problem; however, for the record, my aforementioned failed attempt was to combine the ideas I had for what in my original post I described as the former and latter cases: `perl -0pe 's/(.?\n?([^ \n].?)\n\n.\|.?\n([^ \n].?)\n\n.)/$1/gs' +file.txt` [download] This simply returned the whole file, and I thought it had something to do with the nested parentheses altering what `$1` refers to. When I rewrite it correctly, as per haukex's helpful advice: `perl -0pe 's/(?\|.?\n?([^ \n].?)\n\n.\|.?\n([^ \n].?)\n\n.)/$1/gs +' file.txt` [download] it does return something, but that something is the desired output only in the case where the first line is non-indented. The reason, obviously, is that I was making a stupid mistake: the first alternative returns a match whether or not the first line of `file.txt` is indented, so that code is never going to return the output of: `perl -0pe 's/.?\n([^ \n].?)\n\n.*/$1/gs' file.txt` [download] As I said, it's a moot point, but I thought this follow-up was worth mentioning in case someone who lands on this page learns from my stupid mistake. Regards, Maneesh	[reply] [d/l] [select]

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Re^3: matching first paragraph satisfying condition
by mnshptl32 (Initiate) on Aug 20, 2019 at 18:07 UTC

Thank you, haukex, for the information about the correct use of the branch reset, and sorry for making you guess my incorrect code. It was (and is) a bit of a moot point, since I've been given multiple perl solutions to my problem; however, for the record, my aforementioned failed attempt was to combine the ideas I had for what in my original post I described as the former and latter cases:

perl -0pe 's/(.*?\n*?([^ \n].*?)\n\n.*|.*?\n([^ \n].*?)\n\n.*)/$1/gs' 
+file.txt
[download]

$1

perl -0pe 's/(?|.*?\n*?([^ \n].*?)\n\n.*|.*?\n([^ \n].*?)\n\n.*)/$1/gs
+' file.txt
[download]

it does return something, but that something is the desired output only in the case where the first line is non-indented. The reason, obviously, is that I was making a stupid mistake: the first alternative returns a match whether or not the first line of file.txt is indented, so that code is never going to return the output of:

perl -0pe 's/.*?\n([^ \n].*?)\n\n.*/$1/gs' file.txt
[download]

As I said, it's a moot point, but I thought this follow-up was worth mentioning in case someone who lands on this page learns from my stupid mistake.

Regards,

Maneesh

[reply]
[d/l]
[select]