Re^2: Strange regex to test for newlines: /.*\z/

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Re^3: Strange regex to test for newlines: /.*\z/ by shmem (Chancellor) on May 21, 2007 at 14:26 UTC
Because in a //m, the end of string matching "f\n" is set before the '\n' if the '\n' is trailing. The '\n' is skipped in the match, but the position after "f" isn't the end of the string: perl -D512 -e '$_ = "f\n";/.\z/' Compiling REx `.\z' size 4 Got 36 bytes for offset annotations. first at 2 rarest char at 0 1: STAR(3) 2: REG_ANY(0) 3: EOS(4) 4: END(0) floating ""$ at 0..2147483647 (checking floating) anchored(MBOL) impli +cit minlen 0 Offsets: [4] 2[1] 1[1] 3[2] 5[0] Omitting $` $& $' support. EXECUTING... Guessing start of match, REx ".\z" against "f "... Found floating substr ""$ at offset 1... Position at offset 0 does not contradict /^/m... Guessed: match at offset 0 Matching REx ".\z" against "f " Setting an EVAL scope, savestack=3 0 <> <f > \| 1: STAR REG_ANY can match 1 times out of 2147483647 +... Setting an EVAL scope, savestack=3 1 <f> < > \| 3: EOS failed... failed... Guessing start of match, REx ".\z" against " "... Found floating substr ""$ at offset 0... Position at offset 0 does not contradict /^/m... Guessed: match at offset 0 Setting an EVAL scope, savestack=3 1 <f> < > \| 1: STAR REG_ANY can match 0 times out of 2147483647 +... Setting an EVAL scope, savestack=3 1 <f> < > \| 3: EOS failed... failed... Match failed Freeing REx: `".\\z"' [download] The matching isn't extended after the "\n". Whereas here perl -D512 -e '$_ = "f\n";/.\z/s' Compiling REx `.\z' size 4 Got 36 bytes for offset annotations. first at 2 rarest char at 0 1: STAR(3) 2: SANY(0) 3: EOS(4) 4: END(0) floating ""$ at 0..2147483647 (checking floating) anchored(SBOL) impli +cit minlen 0 Offsets: [4] 2[1] 1[1] 3[2] 5[0] Omitting $` $& $' support. EXECUTING... Guessing start of match, REx ".\z" against "f "... Found floating substr ""$ at offset 1... Guessed: match at offset 0 Matching REx ".\z" against "f " Setting an EVAL scope, savestack=6 0 <> <f > \| 1: STAR SANY can match 2 times out of 2147483647... Setting an EVAL scope, savestack=6 2 <f > <> \| 3: EOS 2 <f > <> \| 4: END Match successful! Freeing REx: `".*\\z"' [download] you can see that the '\z' (`<>` in the debug output) is found after the "\n": `Setting an EVAL scope, savestack=6 2 <f > <> \| 3: EOS 2 <f > <> \| 4: END` [download] --shmem _($_=" "x(1<<5)."?\n".q·/)Oo. G°\ / /\_¯/(q / ---------------------------- \__(m.====·.(_("always off the crowd"))."· ");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}	[reply] [d/l] [select]
Re^4: Strange regex to test for newlines: /.*\z/ by moritz (Cardinal) on May 21, 2007 at 15:10 UTC
Sorry, I still don't get it. Obviously /\z/ matches the string "f\n", so why should it fail to match if I prepend it with something that matches the empty string? This should be independent of where the end of the string is considered to be. And why does /.?\z/ match and /.\z/ not? If we expand that scheme, why does /.?.?\z/ match, and /..?\z/ not? In all cases I'd expect .? and .* to be reduced to the empty string - why doesn't it happen?	[reply]
Re^5: Strange regex to test for newlines: /.*\z/ by shmem (Chancellor) on May 21, 2007 at 15:47 UTC
Now I'm confused as well, my mental model doesn't seem to fit (at least not everywhere :-) Maybe demerphq could tell? --shmem _($_=" "x(1<<5)."?\n".q·/)Oo. G°\ / /\_¯/(q / ---------------------------- \__(m.====·.(_("always off the crowd"))."· ");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}	[reply]
Re^6: Strange regex to test for newlines: /.*\z/ by demerphq (Chancellor) on May 21, 2007 at 23:42 UTC
Re^7: Strange regex to test for newlines: /.*\z/ by tinita (Parson) on May 22, 2007 at 08:20 UTC
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Re^4: Strange regex to test for newlines: /.*\z/ by tinita (Parson) on May 21, 2007 at 14:53 UTC
i personally would be interested in why the following happens: `"\n" =~ /\n.\z/; # matches "\n" =~ /.\z/; # doesn't match. i would expect it to match "\n" =~ /[^\n]\z/; # matches. like expected. but [\n] is like .*` [download] /s or not /s doesn't have to do something with this, or at least it shouldn't, i think.	[reply] [d/l]
Re^5: Strange regex to test for newlines: /.*\z/ by shmem (Chancellor) on May 21, 2007 at 15:44 UTC
`"\n" =~ /\n.\z/; # matches` [download] Obvious, I think. You match a "\n", then EOS (end of string). `"\n" =~ /.\z/; # doesn't match. i would expect it to match` [download] `perl -D512` tells `anchored(MBOL)` (i.e. multiline beginning of line, see perldebguts) with that one, which anchoring doesn't happen with `"\n" =~ /[^\n]\z/; # matches. like expected. but [\n] is like .*` [download] but why? `"\n" =~ /.?\z/;` [download] matches, as does `"\n" =~ /.{0,}\z/;` [download] I can't get a mental model of why the previous one should, but the next one should not match: `"f\n" =~ /.?f\z/;` [download] Weird. Rather inconsistent, if not buggy. --shmem _($_=" "x(1<<5)."?\n".q·/)Oo. G°\ / /\_¯/(q / ---------------------------- \__(m.====·.(_("always off the crowd"))."· ");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}	[reply] [d/l] [select]
Re^6: Strange regex to test for newlines: /.*\z/ by betterworld (Curate) on May 22, 2007 at 00:46 UTC


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