Character class in an array

nikto has asked for the wisdom of the Perl Monks concerning the following question:

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Re: Character class in an array by dws (Chancellor) on Sep 17, 2002 at 17:21 UTC
This works well, except that it also accepts space(' ') as a valid character. This is because of array interpolation, which uses the contents of `$"` to separate array elements when joining them together. You can use this to your advantage by doing something like `@a = ( 'a', 'x', 'z' ); # simplified array while(<>) { local $" = ""; print if(/^[@a]{3}$/); }` [download] Note that this re-localizes `$"` within a loop, which isn't the most effecient approach, but then again you might not notice the performance difference without a microsocope.	[reply] [d/l] [select]
Re: Character class in an array by Nemp (Pilgrim) on Sep 17, 2002 at 17:18 UTC
Hi, If I understand your problem correctly it is being caused by the default list seperator `$"` which is set to a space as default. This is used to seperate array values interpolated into a string hence your regex is also allowing spaces in the character class, which I believe is becoming `[a x z]` in your example above. I tried code similar to yours with the following line added before the interpolation and it worked fine for me. `$" = '';` HTH, Neil Note: all opinion in this post is from a newbie, "wow I think I understood something!" point of view :)	[reply] [d/l] [select]
Re: Character class in an array by RMGir (Prior) on Sep 17, 2002 at 17:37 UTC
Others have explained that $" is the source of your problem. However, there are other problems with what you're doing. You're repeating that interpolation on every trip through the loop, when you could be using qr// to compile your regex once and then forget about it. Here are some comparisons of a few of the other solutions mentioned in this thread, along with one where the regex is pre-built with qr//. These results are with 5.6.1 on cygwin; YMMV. $ perl testLocal.pl Benchmark: running localWhile, localWhileQR, whileLocal, each for at l +east 3 CPU seconds... localWhile: 4 wallclock secs ( 3.02 usr + 0.00 sys = 0.02 CPU) @ 28 +894.20/s (n=87116) localWhileQR: 4 wallclock secs ( 3.17 usr + 0.01 sys = 3.18 CPU) @ +45765.70/s (n=145718) whileLocal: 4 wallclock secs ( 3.09 usr + 0.00 sys = 3.09 CPU) @ 20 +884.62/s (n=64617) Rate whileLocal localWhile localWhileQR whileLocal 20885/s -- -28% -54% localWhile 28894/s 38% -- -37% localWhileQR 45766/s 119% 58% -- [download] The benchmark code is here: Read more... (1233 Bytes) -- Mike	[reply] [d/l] [select]
Re: Re: Character class in an array by Fastolfe (Vicar) on Sep 17, 2002 at 22:05 UTC
You're repeating that interpolation on every trip through the loop, when you could be using qr// to compile your regex once and then forget about it. The `/o` flag on the regex will also work without requiring him to create a regex scalar with qr//.	[reply] [d/l]
Re: Re: Re: Character class in an array by PodMaster (Abbot) on Sep 18, 2002 at 02:50 UTC
And it may not work always. See 'o' modifier clarification needed `____________________________________________________` ** The Third rule of perl club is a statement of fact: pod is sexy.	[reply]
Re: Re: Re: Re: Character class in an array by Fastolfe (Vicar) on Sep 21, 2002 at 18:25 UTC
Re^3: Character class in an array by Aristotle (Chancellor) on Sep 17, 2002 at 22:08 UTC
But will fail if the regex is used multiple times with varying array contents. Makeshifts last the longest.	[reply]
Re: Re^3: Character class in an array by Fastolfe (Vicar) on Sep 21, 2002 at 18:23 UTC
Re^5: Character class in an array by Aristotle (Chancellor) on Sep 21, 2002 at 22:25 UTC
Re: Character class in an array by fglock (Vicar) on Sep 17, 2002 at 17:13 UTC
you are getting `[a x z]` instead of `[axz]` when you say `[@a]` Are you sure your `join` used an empty string? That is, `''` instead of `' '` Try: `$tmp = join('',@a); print if /^[$tmp]{3}$/;` [download]	[reply] [d/l] [select]
Re: Character class in an array by japhy (Canon) on Sep 17, 2002 at 17:32 UTC
You can localize `$"` to the empty string, or just use a scalar instead: `my @a = qw( a x z ); { local $" = ""; while (<>) { print if /^[@a]{3}$/; # /o might be good, too } }` [download] or `my @a = qw( a x z ); my $re = join '', @a; while (<>) { print if /^$re$/; # again, /o might help }` [download] _____________________________________________________ Jeff`[japhy]`Pinyan: Perl, regex, and perl hacker, who'd like a job (NYC-area) `s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;`	[reply] [d/l] [select]
Re: Character class in an array by zigdon (Deacon) on Sep 17, 2002 at 17:16 UTC
When I tried to use this code with the `join('', @a)` everything worked ok? I think that what's happening here is that `@a` is getting interpolated as if in a double quoted string - with $" as as the seperator, which is space by default. The fact that it works with the `join` seems to agree with this theory. -- Dan	[reply] [d/l] [select]
Re: Character class in an array by BrowserUk (Patriarch) on Sep 17, 2002 at 17:20 UTC
Update: nemp's post above this got it first and got it right. It should be $" not $, Below corrected. `@a = ( 'a', 'x', 'z' ); # simplified array { # restrict scope of changes to $, local $"=''; # change from default space to null string while(<>) { print if(/^[@a]{3}$/); } }` [download] Cor! Like yer ring! ... HALO dammit! ... 'Ave it yer way! Hal-lo, Mister la-de-da. ... Like yer ring!	[reply] [d/l]
Re: Character class in an array by Aristotle (Chancellor) on Sep 17, 2002 at 21:23 UTC
Another option over using `$"` is to inline the join in your regex. `my @a = ( 'a', 'x', 'z' ); my $match = qr/^[@{[ join '', @a ]}]{3}$/; while(<>) { print if /$match/; }` [download] You can embed Perl inside any literal strings in this fashion. Makeshifts last the longest.	[reply] [d/l]


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