Hi Tom,
> On 03 Jul 2015, at 14:07, Tom Browder <[email protected]> wrote:
>
> I originally had problems with the S32 description of string function
> index. S32 says that if the substring is not found then a bare Int is
> returned which evaluates to false, otherwise an Int with the position
> of the first substring match is returned. It goes on to say that one
> should not evaluate the result as a number. So my question was, how
> does one practically use that information for a substring that starts
> at position zero which evaluates as false?
>
> Based on the S32 description, I first tried this to remove a comment
> from a data line:
>
> my $str = '# a comment';
> my $idx = $str.index('#');
> if $index && $index >= 0 {
> $str = $str.substr(0, $idx);
> }
>
> It didn't work for a comment at position zero but it found one at any
> other position or no comment at all. Then I tried this:
>
> if $idx {
> $str = $str.substr(0, $idx);
> }
>
> Same result as the previous method: it would not report a substring at
> position zero.
>
> So what am I doing wrong for finding position zero substrings?
Apart from what Carl and yary said, I would like to add that *if* you’re just
interested in knowing whether a string starts with a certain substring, you can
use .starts-with:
my $str = ‘# a comment!’;
say “It’s a comment” if $str.starts-with(“#”);
Similarly, if you’re interested in a certain substring at the end of a string,
you can use .ends-with:
say “Exclamated” if $str.ends-with("!”);
Finally, if you’re interested in a substring at another position in a string,
you can use .substr-eq:
say “Comment at position 4” if $str.substr-eq(“comment”,4);
Hope this helps!
Liz
