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August 2009

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[regex-coach] alternations working differently in Regex Coach versus perl program.
by Troy Peterson 19 Sep '09

19 Sep '09

I am writing a regex to test for valid dates in YYYY-MM-DD format. Using this regex in a perl test program I get positive results for all dates for the next 365 days. Regex Coach however failes to match some such as '2010-06-30'. I assume this is because of the order of the alternations and the regex wanting to match a sub-pattern as quickly as possible. I can resolve the issue in The Regex Coach by adding () around the month and year patterns. I would like to know why there is a difference between my Perl program and Regex Coach. Could this be implementation dependent. Both my program and its output are below. I tend to think that The Regex Coach got this right. (?# regex in The Regex Coach) * [123456789]\d\d\d- # year * * (?: * * (?:0[13578]|10|12 - [012][123456789]|10|20|30|31) | # Months with 31 days* * (?:0[469]|11 - [012][123456789]|10|20|30 ) | # Months with 30 days * * (?:02 - [012][12345678]||10|20|19 ) # Febuary* * )* ### perl Test program #!/iw-home/teamsite/iw-perl/bin/iwperl use strict; use warnings; use Carp; use Getopt::Long; use Pod::Usage; use Cwd; use Date::Calc qw(:all); my $dateregex = qr{ [123456789]\d\d\d- # year (?: (?:0[13578]|10|12 - [012][123456789]|10|20|30|31) | # Months with 31 days (?:0[469]|11 - [012][123456789]|10|20|30 ) | # Months with 30 days (?:02 - [012][12345678]||10|20|19 ) # Febuary ) }smx; sub testdate { my ($d) = (@_); print "$d"; if ( $d =~ m{$dateregex}smx ) { print "okay\n"; } else { print "\n"; croak "broken"; } } foreach my $d ( 1 .. 365 ) { my ( $year, $month, $day, $hour, $min, $sec, $doy, $dow, $dst ) = System_Clock(); ( $year, $month, $day, $hour, $min, $sec ) = Add_Delta_DHMS( $year, $month, $day, '0', '0', '0', "$d", '0', '0', '0' ); my $td = sprintf( "%4d-%02d-%02d", $year, $month, $day ); testdate("$td"); } exit; ##OUTPUT 2009-08-03okay 2009-08-04okay 2009-08-05okay 2009-08-06okay 2009-08-07okay 2009-08-08okay 2009-08-09okay 2009-08-10okay 2009-08-11okay 2009-08-12okay 2009-08-13okay 2009-08-14okay 2009-08-15okay 2009-08-16okay 2009-08-17okay 2009-08-18okay 2009-08-19okay 2009-08-20okay 2009-08-21okay 2009-08-22okay 2009-08-23okay 2009-08-24okay 2009-08-25okay 2009-08-26okay 2009-08-27okay 2009-08-28okay 2009-08-29okay 2009-08-30okay 2009-08-31okay 2009-09-01okay 2009-09-02okay 2009-09-03okay 2009-09-04okay 2009-09-05okay 2009-09-06okay 2009-09-07okay 2009-09-08okay 2009-09-09okay 2009-09-10okay 2009-09-11okay 2009-09-12okay 2009-09-13okay 2009-09-14okay 2009-09-15okay 2009-09-16okay 2009-09-17okay 2009-09-18okay 2009-09-19okay 2009-09-20okay 2009-09-21okay 2009-09-22okay 2009-09-23okay 2009-09-24okay 2009-09-25okay 2009-09-26okay 2009-09-27okay 2009-09-28okay 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