Problem extracting date with regex

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

While searching a text file for dates, this program prints the text surrounding the date as well, but is only supposed to print the date. I have obviously missed something, any suggestions would be appreciated.

$dir = 'C:/texts/';
opendir(directory, $dir) or die "cant";
while ( $file = readdir directory)
{
    next if $file=~/^\./;
    $rfname = $dir.$file;
    # print "Found file: '$rfname'\n";
    open (CONT, $rfname);
    while (<CONT>)
    {
        if ( $_ =~ m/[0-3]?[0-9(th)?(st)?(nd)?(rd)?]\s+(Jan(uary)?|Feb
+(ruary)?|Mar(ch)?|Apr(il)?|May|Jun(e)?|Jul(y)?|Aug(ust)?|Sep(tember)?
+|Oct(ober)?|Nov(ember)?|Dec(ember)?)\s+[0-9]?[0-9]?[0-9][0-9]/ig )
        {
            print "$file\t $_\n";
        }
        elsif ( $_ =~ m/(Jan(uary)?|Feb(ruary)?|Mar(ch)?|Apr(il)?|May|
+Jun(e)?|Jul(y)?|Aug(ust)?|Sep(tember)?|Oct(ober)?|Nov(ember)?|Dec(emb
+er)?)\s+[1-3]?[0-9](th)?(nd)?(st)?(rd)?\s+[0-9]?[0-9]?[0-9][0-9]/ig )
        {
            print "$file\t $_\n";
        }
    }

}
[download]

Petruchio Thu Jul 12 01:55:32 EDT 2001: Added code tags.

Comment on Problem extracting date with regex Download Code

Replies are listed 'Best First'.
RE: Problem extracting date with regex by jjhorner (Hermit) on Jun 21, 2000 at 16:46 UTC
When are people going to learn about the `<code>` notation? As best as I can tell, here is what it says: $dir = 'C:/texts/'; opendir(directory, $dir) or die "cant"; while($file=readdir directory) { next if $file =~ /^\./; $rfname = $dir.$file; # print "Found file: '$rfname'\n"; open (CONT, $rfname); while (<CONT>) { if ( $_ =~ m/[0-3]?[0-9(th)?(st)?(nd)?(rd)?]\s+(Jan(uary)?\|Feb +(ruary)?\|Mar(ch)?\|Apr(il)?\|May\|Jun(e)?\|Jul(y)?\|Aug(ust)?\|Sep(tember)? +\|Oct(ober)?\|Nov(ember)?\|Dec(ember)?)\s+[0-9]?[0-9]?[0-9][0-9]/ig ) { print "$file\t $_\n"; } elsif ( $_ =~ m/(Jan(uary)?\|Feb(ruary)?\|Mar(ch)?\|Apr(il)?\|May\| +Jun(e)?\|Jul(y)?\|Aug(ust)?\|Sep(tember)?\|Oct(ober)?\|Nov(ember)?\|Dec(emb +er)?)\s+[1-3]?[0-9](th)?(nd)?(st)?(rd)?\s+[0-9]?[0-9]?[0-9][0-9]/ig ) { print "$file\t $_\n"; } } } [download] Looking at your code, and another response, I see your problem. You are telling it to print the entire string. If you have Learning Perl, by our own merlyn, look at 7.3.2.3, "Parentheses as memory". Also, from Programming Perl: A regular expression in parentheses, (...), matches whatever the regular expression (represented by ...) matches according to Rule 2. Parentheses therefore serve as a grouping operator for quantification. Parentheses also have the side effect of remembering the matched substring for later use in a backreference (to be discussed later). This side effect can be suppressed by using (?:...) instead, which has only the grouping semantics - it doesn't store anything in $1, $2, and so on. Look into spending $60 for the Perl CD Bookshelf. It rocks. J. J. Horner Linux, Perl, Apache, Stronghold, Unix jhorner@knoxlug.org http://www.knoxlug.org/	[reply] [d/l] [select]
Re: Problem extracting date with regex by raflach (Pilgrim) on Jun 21, 2000 at 17:15 UTC
in actual fact, change your line like this, and you should have what you want. `if($_=~m/([0-3]?[0-9(th)?(st)?(nd)?(rd)?]\s+(Jan(uary)?\|Feb(ruary)?\|Ma +r(ch)?\|Apr(il)?\|May\|Jun(e)?\|Jul(y)?\|Aug(ust)?\|Sep(tember)?\|Oct(ober)? +\|Nov(ember)?\|Dec(ember)?)\s+[0-9]?[0-9]?[0-9][0-9])/ig){ print "$file\t $1\n"; }` [download] And do the same for the other line.	[reply] [d/l]
Re: Problem extracting date with regex by davorg (Chancellor) on Jun 21, 2000 at 16:48 UTC
Best to enclose this stuff in <CODE>..</CODE> tags so it looks like this... $dir='C:/texts/'; opendir(directory,$dir) or die "cant"; while($file=readdir directory){ next if $file=~/^\./; $rfname=$dir.$file; # print "Found file: '$rfname'\n"; open (CONT, $rfname); while (<CONT>){ if($_=~m/<a href="/index.pl?node=0-3&lastnode_id=19212">0-3</a>?<a + href="/index.pl?node=0-9%28th%29%3F%28st%29%3F%28nd%29%3F%28rd%29%3F +&lastnode_id=19212">0-9(th)?(st)?(nd)?(rd)?</a>\s+(Jan(uary)?\|Feb(rua +ry)?\|Mar(ch)?\|Apr(il)?\|May\|Jun(e)?\|Jul(y)?\|Aug(ust)?\|Sep(tember)?\|Oct +(ober)?\|Nov(ember)?\|Dec(ember)?)\s+<a href="/index.pl?node=0-9&lastno +de_id=19212">0-9</a>?<a href="/index.pl?node=0-9&lastnode_id=19212">0 +-9</a>?<a href="/index.pl?node=0-9&lastnode_id=19212">0-9</a><a href= +"/index.pl?node=0-9&lastnode_id=19212">0-9</a>/ig){ print "$file\t $_\n"; } elsif($_=~m/(Jan(uary)?\|Feb(ruary)?\|Mar(ch)?\|Apr(il)?\|May\|Jun(e)?\| +Jul(y)?\|Aug(ust)?\|Sep(tember)?\|Oct(ober)?\|Nov(ember)?\|Dec(ember)?)\s+ +<a href="/index.pl?node=1-3&lastnode_id=19212">1-3</a>?<a href="/inde +x.pl?node=0-9&lastnode_id=19212">0-9</a>(th)?(nd)?(st)?(rd)?\s+<a hre +f="/index.pl?node=0-9&lastnode_id=19212">0-9</a>?<a href="/index.pl?n +ode=0-9&lastnode_id=19212">0-9</a>?<a href="/index.pl?node=0-9&lastno +de_id=19212">0-9</a><a href="/index.pl?node=0-9&lastnode_id=19212">0- +9</a>/ig){ print "$file\t $_\n"; } } } [download] Looking at your code, it prints out the name of the file and the complete line when the line matches the regular expression. If that's not what you want then you'll need to capture part of the match using brackets and print the value of $1, not $_. -- http://www.dave.org.uk European Perl Conference - Sept 22/24 2000 http://www.yapc.org/Europe/	[reply] [d/l]
RE: Re: Problem extracting date with regex by Adam (Vicar) on Jun 22, 2000 at 05:21 UTC
Please DONT do that. When using the <code> tags, or <pre> tags for that matter, please avoid long lines. They mess up the whole page for everyone. Thank you.	[reply]
Re: Problem extracting date with regex ('x' regex modifier) by Russ (Deacon) on Jun 22, 2000 at 01:18 UTC
While on the discussion of code tags, let me mention the x regexp modifier. It lets you use whitespace in your regular expressions for greater readability. `m/[0-3]? [0-9(th)?(st)?(nd)?(rd)?] \s+ (Jan(uary)?\| Feb(ruary)?\| Mar(ch)?\| Apr(il)?\| May\| Jun(e)?\| Jul(y)?\| Aug(ust)?\| Sep(tember)?\| Oct(ober)?\| Nov(ember)?\| Dec(ember)?) \s+ [0-9]?[0-9]?[0-9][0-9]/igx;` [download] The extra whitespace makes it far easier to follow (and doesn't make the browser screen width 4000 pixels wide. ;-) Russ	[reply] [d/l]