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Matching first Letters of two words

by Anonymous Monk
on Apr 20, 2009 at 21:48 UTC ( #758811=perlquestion: print w/replies, xml ) Need Help??

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

Is it possible to check if two words start with the same letter ignoring the case? Thanks in advance

Replies are listed 'Best First'.
Re: Matching first Letters of two words
by moritz (Cardinal) on Apr 20, 2009 at 21:49 UTC
    Sure it is. perlretut has a nice introduction, you should read it, especially the part about backreferences.
Re: Matching first Letters of two words
by linuxer (Curate) on Apr 20, 2009 at 21:50 UTC

      Since the requirement mentioned ignoring case, pointers to lc and uc might also be helpful given your approach.

      Cheers,

      JohnGG

Re: Matching first Letters of two words
by rcaputo (Chaplain) on Apr 21, 2009 at 01:47 UTC

    This example fails because it'll also return true if non-alphabetic characters match. You specified "letters".

    sub first_character_matches { return( ((lc shift) ^ (lc shift)) =~ /^\0/ ); }

    And a command-line version to play with:

    1) poerbook:~% perl -wle 'print "yes" if ( ((lc shift) ^ (lc shift)) = +~ /^\0/ )' abc DBC 1) poerbook:~% perl -wle 'print "yes" if ( ((lc shift) ^ (lc shift)) = +~ /^\0/ )' abc ABC yes

      Here is a solution that detects when initial alphas of separate strings are the same regardless of case, and that I think is immune to differences in the locale or the Unicode character set that may be in effect. My understanding of the effects of locale and Unicode on regex behavior continues to be a bit vague.

      I would be interested in any comments, links, etc., from other monks on my notions that:

      1. The regex expression  [^\W\d_] matches an alpha character regardless of locale or the ASCII or Unicode character set in effect during compilation of the script.
      2. The expressions  [[:alpha:]] and  [^\W\d_] have exactly the same behavior.
      3. The  //o modifier of the  m{ \A ([^\W\d_]) }xmso regex prevents re-compilation of the regex on multiple calls and so is, in theory, more efficient.
      4. After two strings in which the first characters are identical have been bitwise-xored in the expression  ((lc str1) ^ (lc str2)) =~ /^\0/, the regex  /^\0/ is not guaranteed always to match with the first character of the resultant string regardless of locale or character set.
      >perl -wMstrict -le "print '----- output -----'; while (my ($word1, $word2) = splice @ARGV, 0, 2) { print qq{:$word1: and :$word2: initial letters }, first_letter_matches($word1, $word2) ? 'same' : 'different'; } sub first_letter_matches { my ($w1, $w2) = @_; return $w1 =~ m{ \A ([^\W\d_]) }xmso && $w2 =~ m{ \A $1 }xmsi ; } " a a a A Ab abc b b abcd A A1% a2# "" "" "" a a "" a b a bc ab c 123 123 %# %# ----- output ----- :a: and :a: initial letters same :a: and :A: initial letters same :Ab: and :abc: initial letters same :b: and :b: initial letters same :abcd: and :A: initial letters same :A1%: and :a2#: initial letters same :: and :: initial letters different :: and :a: initial letters different :a: and :: initial letters different :a: and :b: initial letters different :a: and :bc: initial letters different :ab: and :c: initial letters different :123: and :123: initial letters different :%#: and :%#: initial letters different

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