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Thread: Perl help

  1. #1
    Join Date
    Aug 2008
    Posts
    7

    Unanswered: Perl help

    hello all,

    I am very new to perl and kindly advice me to get the ouput. Below is my perl full code through which I am trying to match the word pattern existing in the actual sentenes (i.e) input file - sentences.txt. You can see the sentences in the beginning of the code. The pharses are splitted in to words and the first character is removed in order to avoid letter case and replaced with a character class [A-z] for matching the pattern.

    Actually this pattern is derived at the end of subroutine and stored as an array value @array_return. But after this, I am really struggling to continue or change the array to scalar where I can match the sentence on the left hand and pattern on the right hand side. The variable imagined now for the pattern is $pattern (in the code). I would like to get my output as:

    $pattern --- matched sentence ---- $sentences
    (for eg): dungeons & dragons --- matched sentence --- dungeons & dragons is a movie

    Please help me to solve this problem. When I try to run the below code, I am getting the error message as below for all sentences in the file.

    Use of uninitialized value in concatenation (.) or string at phase2.pl line 42, <DAT> line 1.
    Use of uninitialized value in concatenation (.) or string at phase2.pl line 43, <DAT> line 1.
    --- matched --- history of oakland, california is in San Francisco

    Actual Code:
    -------------------
    #! /usr/bin/perl -w
    # to split comma and space in a sentence

    #given sentences in a file containing phrases to match
    #$sentence1 = "history of oakland, california is in San Francisco";
    #$sentence2 = "earth, wind & fire albums has a good rhythm";
    #$sentence3 = "at&t United States is a company";
    #$sentence4 = "dungeons & dragons is a movie";

    $phrase1 = "history of oakland, california";
    $phrase2 = "earth, wind & fire albums";
    $phrase3 = "at&t United States";
    $phrase4 = "dungeons & dragons";

    #putting all phrases in to an array
    my @phrases = ($phrase1, $phrase2, $phrase3, $phrase4);
    foreach $new (@phrases) {
    print STDERR "the whole phrase is: $new\n";
    #defining a subroutine procedure by a variable name and calling the subroutine
    @array_return = procedure($new);
    print STDERR "the pattern is: @array_return\n";
    while (@array_return) {
    print STDERR "value is: $array_return[0]\n";
    shift @array_return;
    }
    #open a data file containing the sentences with the phrases to be matched
    open(DAT, "sentences.txt") || die "Couldn't open the file\n";
    while (defined ($sentences = <DAT>)) {
    #match the words in the file
    if ($sentences =~ m/^($pattern)/) {
    print STDERR "$pattern --- matched --- $sentences\n";
    }elsif ($sentences =~ m/\b$pattern\b/) {
    print STDERR "$pattern --- matched in word boundary --- $sentences\n";
    }
    }
    close DAT;
    }

    #defining subroutine
    sub procedure {
    my ($string) = @_;
    print STDERR "String is: $string\n";
    my @words = split(/, (?!\W)|\s|(?<=\W) &/, $string);
    print STDERR "words are: @words\n";
    my $match = "";
    foreach $word (@words) {
    print STDERR "the words after splitting are: $word\n";
    #removing the first character to avoid case conversion
    my $first = substr($word, 1);
    my $newword = "[A-z&]".$first;
    print STDERR "word after removing first letter: $newword\n";
    $match = $match." ".$newword;
    print STDERR "concatenated word is: $match\n";
    }
    return $match;
    }

  2. #2
    Join Date
    Sep 2008
    Posts
    2

    Exclamation

    There are some odd things about your program, so I'll try to send up some points your way:

    First, apart from the warning tag (-w), put this on the top of your program:
    Code:
    use strict;
    This will catch a lot of errors, mostly global variables and those out of scope.

    When opening a file and reading from it, the cannonical, and better way is to write:

    Code:
    open(my $DAT, '<', "sentences.txt") || die "Couldn't open the file - $!\n";
    foreach my $sentences (<$DAT>)
    Now, in your code, this:
    Code:
    if ($sentences =~ m/^($pattern)/) {
    	warn "$pattern --- matched --- $sentences\n";
    }
    elsif ($sentences =~ m/\b$pattern\b/) {
    	warn "$pattern --- matched in word boundary --- $sentences\n";
    }
    doesn't work, since $pattern isn't defined anywhere.

    Now, the procedure "procedure", I've pointed some of the more obvious points in comments:

    Code:
    sub procedure {
    	my ($string) = @_; # preferable my $string = shift; 
            warn "String is: $string\n";
    	my @words = split(/, (?!\W)|\s|(?<=\W) &/, $string);
    	warn "words are: @words\n"; 
    	my $match = "";
    	foreach my $word (@words) {
    		warn "the words after splitting are: $word\n";
    		my $first = substr($word, 1);
    		my $newword = "[A-z&]".$first; # for 'word' this prints '[A-z&]ord'
    		warn "word after removing first letter: $newword\n";
    		$match = $match." ".$newword; #$match is "", $newword is '[A-z&]ord'
    		warn "concatenated word is: $match\n";
    	}
    	return $match; #this is a scalar, you call it in list context ?!?
    }
    Hope this gives you some ideas

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