On 10 Feb, 2012, at 0:31, Jim Gibson <jimsgib...@gmail.com> wrote:
> At 12:44 PM +0800 2/9/12, lina wrote:
>> #!/usr/bin/perl
>> use strict ;
>> my @strings = ( "Fred and Barney",
>> "Gilligan or Skipper",
>> "Fred and Ginger"
>> );
>> foreach my $string (@strings)
>> {
>> $string =~ m/(\S+)(and|or)(\S+)/;
>>
>> print "\$1: $1\n\$2: $2\n\$3: $3\n";
>> print "-" x 10, "\n";
>> } ;
>>
>> Why the results is:
>>
>> $ ./grouping_example.pl
>> $1:
>> $2:
>> $3:
>> ----------
>> $1:
>> $2:
>> $3:
>> ----------
>> $1:
>> $2:
>> $3:
>> ----------
>>
>> no value output?
>
> The reason is that your match did not succeed (as others have pointed out and
> given you regular expressions that work).
>
> It is important to test the success of the match before you use the captured
> values. You should also add 'use warnings;' to your program. Had
yes. It's a very good point.
I wished to use warnings, but mistook use strict as use warnings.
I'm going to check what's "use strict " for?
> you done that, Perl would have told you that no values were captured.
>
> If the match is not successful, then Perl will not reset the capture
> variables:
>
> __program__
>
> #!/usr/bin/perl
> use strict;
> use warnings;
>
> my @strings = (
> "FredandBarney", # spaces removed so match will succeed
Before I used TAB just to make it look good. didn't realize it's spaces
sensitive.
> "Gilligan or Skipper",
> "Fred and Ginger"
> );
> foreach my $string (@strings) {
> $string =~ m/(\S+)(and|or)(\S+)/;
> print "<$1> <$2> <$3>\n";
> };
>
> __output__
>
> <Fred> <and> <Barney>
> <Fred> <and> <Barney>
> <Fred> <and> <Barney>
>
> So you should always do something like this:
>
> #!/usr/bin/perl
> use strict;
> use warnings;
>
> my @strings = (
> "FredandBarney",
> "Gilligan or Skipper",
> "Fred and Ginger"
> );
> foreach my $string (@strings) {
> if( $string =~ m/(\S+)(and|or)(\S+)/ ) {
> print "<$1> <$2> <$3>\n";
> }else{
> print "No match\n";
> }
> };
>
> __output__
> <Fred> <and> <Barney>
> No match
> No match
Thanks for all,
>
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