Help with regexes

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

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Re: Help with regexes by Enlil (Parson) on Jun 30, 2004 at 00:09 UTC
Hello monks. I am a n00b and I am trying to fix some scripts that i didnt write and I am stumped on a regular expression If you have time you might want to peruse the documentation on regexes in general at perlreftut and perlre). As you might run into more regular expressions you might want to look into using YAPE::Regex::Explain which makes deciphering Regexes easy for instance `perl -MYAPE::Regex::Explain -e 'print YAPE::Regex::Explain->new(qr/^(\ +s^+)MVA/o)->explain;'` [download] will return the following for your first regex: The regular expression: (?-imsx:^(\s^+)MVA) 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): ---------------------------------------------------------------------- ^ the beginning of the string ---------------------------------------------------------------------- ( group and capture to \1: ---------------------------------------------------------------------- \s whitespace (\n, \r, \t, \f, and " ") ---------------------------------------------------------------------- ^+ the beginning of the string (1 or more times (matching the most amount possible)) ---------------------------------------------------------------------- ) end of \1 ---------------------------------------------------------------------- MVA 'MVA' ---------------------------------------------------------------------- ) end of grouping ---------------------------------------------------------------------- [download] and then for the second one: perl -MYape::Regex::Explain -e 'print YAPE::Regex::Explain->new(qr/(\s ++)/o)->explain;' The regular expression: (?-imsx:(\s+)) 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): ---------------------------------------------------------------------- ( group and capture to \1: ---------------------------------------------------------------------- \s+ whitespace (\n, \r, \t, \f, and " ") (1 or more times (matching the most amount possible)) ---------------------------------------------------------------------- ) end of \1 ---------------------------------------------------------------------- ) end of grouping ---------------------------------------------------------------------- [download] HTH -enlil	[reply] [d/l] [select]
Re: Help with regexes by ercparker (Hermit) on Jun 29, 2004 at 23:13 UTC
the first one is matching : begin with one or more space followed by MVA and capturing the spaces the second one is replacing : one or more space with nothing the o modifier causes pattern to only be compiled once	[reply]
Re: Help with regexes by borisz (Canon) on Jun 29, 2004 at 23:49 UTC
ercparker says it all. Beside that the `$_ =~` is optional. you can write `/^(\s+)MVA/o s/(\s+)//o` [download] and get the same result. Boris	[reply] [d/l] [select]