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Reg Expression translation

by Anonymous Monk
on Nov 14, 2003 at 19:25 UTC ( #307166=perlquestion: print w/replies, xml ) Need Help??

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

Please help me understand the below reg expressions:
/^\s*$/
means check for all spaces in the entry. Check for beginning spaces and spaces in the middle and ending with a space??
/^\w{1,}@/
Check for beginning with one word only and a '@' ??

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Re: Reg Expression translation
by danger (Priest) on Nov 14, 2003 at 19:39 UTC
    Please help me understand the below reg expressions:
    /^\s*$/
    means check for all spaces in the entry. Check for beginning spaces and spaces in the middle and ending with a space??

    It means: match the beginning of the string, followed by zero or more whitespace characters, followed by the end of the string. Essentially, it matches what we often think of as a "blank" line.

    /^\w{1,}@/
    Check for beginning with one word only and a '@' ??

    Match beginning of string, followed by 1 or more word characters (those being of the class: [a-zA-Z0-9_]) followed by the '@' character.

    To really understand regular expressions better, please see the following documents: perlrequick, perlretut, perlre. Also, Jeffrey Friedl's "Mastering Regular Expressions" is an excellent resource.

Re: Reg Expression translation
by Anonymous Monk on Nov 14, 2003 at 19:52 UTC

    Use YAPE::Regex::Explain.

    $ perl -MYAPE::Regex::Explain -e 'print YAPE::Regex::Explain->new(q(^\ +s*$))->explain' The regular expression: (?-imsx:^\s*$) 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): ---------------------------------------------------------------------- ^ the beginning of the string ---------------------------------------------------------------------- \s* whitespace (\n, \r, \t, \f, and " ") (0 or more times (matching the most amount possible)) ---------------------------------------------------------------------- $ before an optional \n, and the end of the string ---------------------------------------------------------------------- ) end of grouping ---------------------------------------------------------------------- $ perl -MYAPE::Regex::Explain -e 'print YAPE::Regex::Explain->new(q(^\ +w{1,}@))->explain' The regular expression: (?-imsx:^\w{1,}@) 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 ---------------------------------------------------------------------- \w{1,} word characters (a-z, A-Z, 0-9, _) (at least 1 times (matching the most amount possible)) ---------------------------------------------------------------------- @ '@' ---------------------------------------------------------------------- ) end of grouping ----------------------------------------------------------------------
Re: Reg Expression translation
by Albannach (Monsignor) on Nov 14, 2003 at 19:54 UTC
    Provided you do read perlre and the other fine references so that you have a basis for understanding, you might find YAPE::Regex::Explain (by our own japhy) to be of use.

    perl -MYAPE::Regex::Explain -e "print YAPE::Regex::Explain->new(shift)->explain;" "^\s*$"

    yields

    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): ---------------------------------------------------------------------- ^ the beginning of the string ---------------------------------------------------------------------- \s* whitespace (\n, \r, \t, \f, and " ") (0 or more times (matching the most amount possible)) ---------------------------------------------------------------------- $ before an optional \n, and the end of the string ---------------------------------------------------------------------- ) end of grouping ----------------------------------------------------------------------

    --
    I'd like to be able to assign to an luser

Re: Reg Expression translation
by fletcher_the_dog (Friar) on Nov 14, 2003 at 19:54 UTC
    /^\s*$/ is a common way of seeing if a string is empty or has just white space. Basically it matches if from the beginning ("^") to the end ("$") where there is nothing or only white space ("\s*") between.
    /^\w{1,}@/ is just another way of writing /^\w+@/ which matches one or more "word" characters ("\w+") followed by "@" at the beginning of the line ("^")
      thanks to everyone.
Re: Reg Expression translation
by meetraz (Hermit) on Nov 14, 2003 at 20:10 UTC
    One thing you can try is YAPE-Regex-Explain. It works like this:

    use strict; use YAPE::Regex::Explain; my $regex1 = qr/^\s*$/; my $regex2 = qr/^\w{1,}@/; print YAPE::Regex::Explain->new($regex1)->explain; print YAPE::Regex::Explain->new($regex2)->explain;

    (Its a cool module from japhy)

    UPDATE: Whoops, looks like everybody beat me to it!

Re: Reg Expression translation
by hardburn (Abbot) on Nov 14, 2003 at 19:31 UTC

    perlre

    ----
    I wanted to explore how Perl's closures can be manipulated, and ended up creating an object system by accident.
    -- Schemer

    : () { :|:& };:

    Note: All code is untested, unless otherwise stated

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