Re^3: Unescaped left brace in regex is passed through in regex

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Re^4: Unescaped left brace in regex is passed through in regex by Aldebaran (Curate) on Jun 07, 2022 at 20:25 UTC
I try to follow what LanX does with the REPL. I'm confused right now. `$ perl -de1 Loading DB routines from perl5db.pl version 1.53 Editor support available. Enter h or 'h h' for help, or 'man perldebug' for more help. main::(-e:1): 1 DB<1> $str = '\\x{A3f4}' + DB<2> p $str + \x{A3f4}` [download] Ok, so we begin the game with a string that has 2 backslashes before an x and then curly braces containing a value. We ask the debugger to print the value, and the output differs from the original string by having one fewer backslash. Q1) What makes you think this is a left-curly brace? I don't doubt you; I just can't get there: `DB<2> print $str + \x{A3f4} DB<3> print "$str" + \x{A3f4}` [download] Q2) What is \x{value} called? I'm going up a wall trying to disambiguate it. I think it's completely-different from my \x experience with it in a regex: perlre#/x-and-/xx. Continuing: `DB<3> if ( $str =~ /(\\x{[A-F\d]+})/i ) { print $1 } + Unescaped left brace in regex is deprecated here (and will be fatal in + Perl 5.30), passed through in regex; marked by <-- HERE in m/(\\x{ < +-- HERE [A-F\d]+})/ at (eval 13)[/usr/share/perl/5.28/perl5db.pl:738] + line 2.` [download] Ok, let's stop here. When I'm debugging my stuff, I typically think that the first error message is the one I need to attend to. What follows was the stack of things that bombed out because of the first error. This is as clear as an error message is, except that I'm not quite sure where it stops and the next one begins. Let's take a look at the rest of the message: at (eval 13)[/usr/share/perl/5.28/perl5db.pl:738] line 2. eval 'no strict; ($@, $!, $^E, $,, $/, $\\, $^W) = @DB::saved;pack +age main; $^D = $^D \| $DB::db_stop; if ( $str =~ /(\\\\x{[A-F\\d]+})/i ) { print $1 }; ' called at /usr/share/perl/5.28/perl5db.pl line 738 DB::eval called at /usr/share/perl/5.28/perl5db.pl line 3138 DB::DB called at -e line 1 Unescaped left brace in regex is deprecated here (and will be fatal in + Perl 5.30), passed through in regex; marked by <-- HERE in m/(\\x{ < +-- HERE [A-F\d]+})/ at (eval 13)[/usr/share/perl/5.28/perl5db.pl:738] + line 2. at (eval 13)[/usr/share/perl/5.28/perl5db.pl:738] line 2. eval 'no strict; ($@, $!, $^E, $,, $/, $\\, $^W) = @DB::saved;pack +age main; $^D = $^D \| $DB::db_stop; if ( $str =~ /(\\\\x{[A-F\\d]+})/i ) { print $1 }; ' called at /usr/share/perl/5.28/perl5db.pl line 738 DB::eval called at /usr/share/perl/5.28/perl5db.pl line 3138 DB::DB called at -e line 1 Unescaped left brace in regex is deprecated here (and will be fatal in + Perl 5.30), passed through in regex; marked by <-- HERE in m/(\\x{ < +-- HERE [A-F\d]+})/ at (eval 13)[/usr/share/perl/5.28/perl5db.pl:738] + line 2. at (eval 13)[/usr/share/perl/5.28/perl5db.pl:738] line 2. eval 'no strict; ($@, $!, $^E, $,, $/, $\\, $^W) = @DB::saved;pack +age main; $^D = $^D \| $DB::db_stop; if ( $str =~ /(\\\\x{[A-F\\d]+})/i ) { print $1 }; ' called at /usr/share/perl/5.28/perl5db.pl line 738 DB::eval called at /usr/share/perl/5.28/perl5db.pl line 3138 DB::DB called at -e line 1 \x{A3f4} [download] Can you "see" the layering of this, because I cannot. Q3) Is there a setting for the debugger that allows for more human readable error output, maybe a newline between layers? Q4) Why is any part of perl5db.pl asking itself this question: `eval 'no strict; ($@, $!, $^E, $,, $/, $\\, $^W) = @DB::saved;package +main; $^D = $^D \| $DB::db_stop; if ( $str =~ /(\\\\x{[A-F\\d]+})/i ) { print $1 };` [download] There are 4 backslashes before that x. I know this is a situation of garbage in, but how is this the garbage out? `DB<5> $str = '123X12' + DB<6> p $str + 123X12 DB<7> if ( $str =~ /^(\d{2,4})[^\d](\d{2})/) { print "$1;$2" } + 123;12 DB<8> $str = '123{12' + DB<9> if ( $str =~ /^(\d{2,4})[^\d](\d{2})/) { print "$1;$2" } + 123;12` [download] Well, the rest of this makes sense to me, and it shows a use of the curly braces that I might know. I wouldn't understand it without working through it with the REPL. One final question: Q5) Is it said correctly that perl is written in c, but the perl debugger is written in perl? Gruss aus Amiland	[reply] [d/l] [select]
Re^5: Unescaped left brace in regex is passed through in regex by AnomalousMonk (Archbishop) on Jun 07, 2022 at 21:24 UTC
I'm not the best one to answer questions about the Perl debugger, but I can answer some more general questions. Q0) ... we begin the game with a string that has 2 backslashes ... the output differs from the original string by having one fewer backslash. Due to the way the single-quote string constructor handles backslashes (escapes), the `\\` will in this case compile to a single literal backslash. See Quote and Quote-like Operators and the discussion of `q/STRING/` in Quote-Like Operators. Q1) What makes you think this is a left-curly brace? I'm not quite sure what "this" refers to, but do you dispute that there is a left-curly (and a right-curly) in the `\x{A3f4}` string? What else would you call it/them? Q2: What is \x{value} called? ... I would call it (or in this case `\x{A3f4}`) "the string compiled from `'\\x{A3f4}'`". The `\x` part has nothing to do with the `/x` or `/xx` regex modifiers. Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]
Re^6: Unescaped left brace in regex is passed through in regex by Aldebaran (Curate) on Jun 08, 2022 at 00:20 UTC
Due to the way the single-quote string constructor handles backslashes (escapes), the \\ will in this case compile to a single literal backslash. See Quote and Quote-like Operators and the discussion of q/STRING/ in Quote-Like Operators. Thanks for your comment, AM. Your link is a good read and worth reposting. I thought that the collapsing of backslashes was done by the OS in resolving paths. I was unaware that perl did it. do you dispute that there is a left-curly (and a right-curly) in the \x{A3f4} string? What else would you call it/them? I do not dispute that, so this string itself never represents a left curly brace, rather it has a left curly brace in it. I would call it (or in this case \x{A3f4}) "the string compiled from '\\x{A3f4}'" Ok. From the above source we have: `\x{263A} [1,8] hex char (example shown: SMILEY) \x{ 263A } Same, but shows optional blanks inside and adjoining the braces \x1b [2,8] restricted range hex char (example: ESC)` [download] So, I think "aha, it's a hex representation", but then I can't get there with the REPL: `DB<1> $str2='\\x{263}' + DB<2> p $str2 + \x{263} DB<3> p hex $str2 + 0 DB<4> print hex $str2 + 0` [download] I would expect to see a smiley face rather than zero. This is a head-scratcher: `DB<6> $str3='\\\\\\\x{aF}' + DB<7> p $str3 + \\\\x{aF} DB<8> p hex $str3 + 0 DB<9> print hex $str3 + 0` [download] $str3 goes from 7 to 4 backslashes when compiled(?). But I get zero for a hex value no matter what I try: `DB<10> $str4='\x{aF}' + DB<11> p $str4 + \x{aF} DB<12> print hex $str4 + 0 DB<13> print hex 'aF' + 175` [download] How do I tease 175 out of $str4? The \x part has nothing to do with the /x or /xx regex modifiers. That part is clearer now. I have that backslash/forwardslash disphoria going on now where I can hardly see the difference and it looks like a toothpick war. I get the occasional billiken that I read or write the wrong way.	[reply] [d/l] [select]
Re^7: Unescaped left brace in regex is passed through in regex by LanX (Saint) on Jun 08, 2022 at 09:28 UTC
Re^7: Unescaped left brace in regex is passed through in regex by AnomalousMonk (Archbishop) on Jun 08, 2022 at 02:38 UTC
Re^5: Unescaped left brace in regex is passed through in regex by LanX (Saint) on Jun 07, 2022 at 23:35 UTC
> `$str = '\\x{A3f4}'` please note the single quotes, it creates just the string `\x{A3f4}` only two characters need to be escaped inside single-quotes ... the single-quote and consequently the escape-character, which is the backslash. "\x{HEX}" is a notation for hex-character only inside double-quotes, so it seems someone is trying to parse code similar to Perl. I ran the debugger with 5.32 without warnings pre-activated, I'm surprised about your errors. Looks like you ran something like `perl -dwe0` And you are seeing the internal stack-trace of the debugger, I don't wanna comment on the `perldebguts` The debugger is mostly written in Perl, but using hooks written in C. I.O.W. perl5db.pl is written in Perl, but only possible because of the debugging API written in C, expecting to find functions like &DB::DB And there are some old debugging flags available written in C, things I've never used. Greetings from Krautland ;-) Rolf	[reply] [d/l] [select]