Pattern Match n00b

USP45 has asked for the wisdom of the Perl Monks concerning the following question:

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Re: Pattern Match n00b by pc88mxer (Vicar) on Mar 14, 2008 at 20:43 UTC
Doesn't the ;?? mean match semi-colon 0 or 1 times and be non-greedy? Yes, it does, but that's not what you want. You need the `.+` to be non-greedy or else disallow semi-colons in your values: `@{$pets} = $1 if $pet_list =~ /$some_variable\:(.?)(;\|\z)/; # or not allow ';' in values: @{$pets} = $1 if $pet_list =~ /$some_variable\:([^;])(;\|\z)/;` [download] To make the matching more robust, you'll want to do something like this: `@{$pets} = $1 if $pet_list =~ /(?:\A\|;)\Q$some_variable\E\:([^;]*)(;\|\ +z)/;` [download]	[reply] [d/l] [select]
Re: Pattern Match n00b by BrowserUk (Patriarch) on Mar 14, 2008 at 21:02 UTC
Doesn't the ;?? mean match semi-colon 0 or 1 times and be non-greedy? It does, but it only makes that part of the match non-greedy. The `(.+)` remains greedy. But if you make that part non-greedy, then you will be asking to capture as little as possible following the ':', that might or might not be followed by a ';'. Which means it will capture just a single character. A couple of ways to approach the problem: Make capture non-greedy and have a definite terminating condition:`/$some_variable\:(.+?)(?:;\|$)/` Where `(?:;\|$)` requires a semicolon or the end-of-string, (prefering the former) to terminate the capture. Or as you know the bit you want to capture cannot contain a ';', reduce the scope of the capture using `[^;]+` in place of '.' and omit the terminator. `/$some_variable\:([^;]+)/` [download] Either works: `$pet_list = 'dog:boston.terrier;cat:orange.tabby';; $pets=[]; $pet_list =~ /$_\:(.+?)(?:;\|$)/ and push @{$pets},$1 for qw[cat dog]; print for @{$pets};; orange.tabby boston.terrier $pets=[]; $pet_list =~ /$_\:([^;]+)/ and push @{$pets},$1 for qw[cat dog]; print for @{$pets};; orange.tabby boston.terrier` [download] Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply] [d/l] [select]
Re: Pattern Match n00b by skirnir (Monk) on Mar 14, 2008 at 20:59 UTC
No, to make the .+ part non-greedy you'd have to place the '?' directly after the "+": `@{$pets} = $1 if $pet_list =~ /$some_variable\:(.+?);?/;` But as the ';' is optional, the non-greedy match would stop matching after the first non-newline character. In your example you would get "b" in $1. It's best not to use "." if you don't really mean "any non-newline character". In your case I think `[^;]` would be the right thing to use, given that I understood properly what you want to do.	[reply] [d/l] [select]
Re: Pattern Match n00b by jeroenes (Priest) on Mar 14, 2008 at 21:27 UTC
You could go splitting instead. Nested splits on `;` and `:` could work. Or you could do it all in one statement with SuperSplit: `$array=supersplit(':',';',$mystring);` provided that the (semi)colons are true delimiters. Cheers, Jeroen Couldn't resist the temptation after all those years ;-)	[reply] [d/l] [select]


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