how to state this by REL

[whatluo]

I need to check the name to conform to the following conventions: valid names are comprised of only alphanumeric characters(a-z A-Z and 0-9) plus the characters '-', '_', and '.'. Names must begin with a letter.

someone told me to use this

$name =~ /\A[a-zA-Z][\w.-]*\z/;

but it treat "s@--__" and "s!!!@@@___" to valid which should be invalide name, casue \w in perl include @ and ! and punction sign, Any hints on this?

Thanks,
--Whatluo

[pg]

The regexp is correct. The problem is your string. Use single quote instead of double quote, to avoid interpolation. Try this code:

{
    my $name = "s@--__";
    print $name, "\n";
    if ($name =~ /\A[a-zA-Z][\w.-]*\z/) {
        print "match\n";
    } else {
        print "not match\n";
    }
}
{
    my $name = "s!!!@@@___";
    print $name, "\n";
    if ($name =~ /\A[a-zA-Z][\w.-]*\z/) {
        print "match\n";
    } else {
        print "not match\n";
    }
}
{
    my $name = 's@--__';
    print $name, "\n";
    if ($name =~ /\A[a-zA-Z][\w.-]*\z/) {
        print "match\n";
    } else {
        print "not match\n";
    }
}
{
    my $name = 's!!!@@@___';
    print $name, "\n";
    if ($name =~ /\A[a-zA-Z][\w.-]*\z/) {
        print "match\n";
    } else {
        print "not match\n";
    }
}

Which prints:

Possible unintended interpolation of @___ in string at math1.pl line 1
+1.
s-__
match
s!!!@@
not match
s@--__
not match
s!!!@@@___
not match

[whatluo]

>The regexp is correct. The problem is your string. Use single 
>quote instead of double quote, to avoid interpolation.

Yes, I got it, Now I use single quote to make it happy, and I 
want to know what's really means as to \w in perl, do it 
include @ ! or not?

Thanks for the info.

[Aragorn]

According to the perlre documentation, it doesn't:

A "\w" matches a single alphanumeric character (an alphabetic character, or a decimal digit) or "_", not a whole word.

Arjen

[Errto]

casue \w in perl include @ and ! and punction sign,

This isn't true. See the following example,

print "no match" unless 's!!!@@@___' =~ /\A[a-zA-Z][\w.-]*\z/;

which prints "no match." \w only matches letters, digits, and underscores. Maybe you could show us an example program where this is happening so we can provide some better advice.

[reasonablekeith]

While the guy who gave you this regex obviously knows what he's doing, and admittedly, it does function according to spec, I'd still change it.

The simple reason being I had to lookup what \A and \z do. Far more common anchors for matching the beginning and end of strings are ^ and $. Even the documentation describes them as "The two most common anchors".

so I'd change it to

 $name =~ /^[a-zA-Z][\w.-]*$/

I might even be tempted to explicitly escape that '.', even though it's not strictly necessary.

 $name =~ /^[a-zA-Z][\w\.-]*$/

To me, that makes it more obvious that we're matching a dot.

I wonder what percentage of 'average ability' Perl programmers could tell you the subtle difference between \z and \Z without reference to a manual?

[herveus]

Howdy!

I wouldn't change that RE. Since you had to look up \A and \z, did you also look up ^ and $? They don't do what you say they do. \A and \z do exactly what you attribute to ^ and ?.

Further, escaping . in a character class is gratuitous.

To elaborate: ^ matches the beginning of the line, while $ matches the end of the line (unless the line ends with a newline, in which case the anchor matches before the newline. \A is always the start of the string. \z is always the end of the string. ^ and $ depend on whether you are using the /m modifier or not.

TheDamian makes fair arguments for using \A and \z (along with /x, /m, and /s routinely). The core argument is that doing so makes your regexen behave with less surprising behavior all the time. Consistency, and all that.