Regular Expression mystery

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

Replies are listed 'Best First'.
Re: Regular Expression mystery by PodMaster (Abbot) on Sep 20, 2002 at 11:15 UTC
Don't ever guess again. use YAPE::Regex::Explain; die YAPE::Regex::Explain->new(qr/.${name}-/)->explain; __END__ The regular expression: (?-imsx:.-) matches as follows: NODE EXPLANATION ---------------------------------------------------------------------- (?-imsx: group, but do not capture (case-sensitive) (with ^ and $ matching normally) (with . not matching \n) (matching whitespace and # normally): ---------------------------------------------------------------------- .* any character except \n (0 or more times (matching the most amount possible)) ---------------------------------------------------------------------- -* '-' (0 or more times (matching the most amount possible)) ---------------------------------------------------------------------- ) end of grouping ---------------------------------------------------------------------- [download] update: In case you were wondering where the (?-imsx:.-) comes from, well `perl -e"print qr/asdf/"`, `perl -e"print ref qr/a/"` and since ${name} is not defined anywhere in the above snippet, that part don't show up in the explanation. Here's an alternative use YAPE::Regex::Explain; my $name = 'asdf'; die YAPE::Regex::Explain->new(qr/.${name}-/)->explain; __END__ The regular expression: (?-imsx:.asdf-) matches as follows: NODE EXPLANATION ---------------------------------------------------------------------- (?-imsx: group, but do not capture (case-sensitive) (with ^ and $ matching normally) (with . not matching \n) (matching whitespace and # normally): ---------------------------------------------------------------------- .* any character except \n (0 or more times (matching the most amount possible)) ---------------------------------------------------------------------- asdf 'asdf' ---------------------------------------------------------------------- -* '-' (0 or more times (matching the most amount possible)) ---------------------------------------------------------------------- ) end of grouping ---------------------------------------------------------------------- [download] `____________________________________________________` ** The Third rule of perl club is a statement of fact: pod is sexy.	[reply] [d/l] [select]
Re: Re: Regular Expression mystery by Anonymous Monk on Sep 20, 2002 at 12:06 UTC
I got alot of answers here. Thanks so much to all of you!	[reply]
Re: Regular Expression mystery by davorg (Chancellor) on Sep 20, 2002 at 11:13 UTC
`.` - zero or more of any character `${name}` - the contents of $name `-` - zero or more '-' characters. -- <http://www.dave.org.uk> "The first rule of Perl club is you do not talk about Perl club." -- Chip Salzenberg	[reply]
Re: Regular Expression mystery by thinker (Parson) on Sep 20, 2002 at 11:18 UTC
Hi Imagine the variable $name contained "foo", the regex will expand to .foo- , which will be true if the line contains any character, followed somewhwere with foo, and one or more - signs. cheers thinker update As can be seen in the replies from the less careless monks who posted before me, the - sign need not appear. apologies.	[reply]


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