[RESOLVED] preg_match()

xbuilder

Hi,

Why the following returns 1. I though it should be 0 (no match) because it specifies a maximum of 5 chars.

    print preg_match("/[A-Za-z]{3,5}/", "JohnSmith")."<br>";

laserlight

The pattern matches 3 to 5 consecutive letters. "JohnSmith" certainly has 3 to 5 consecutive letters, so there is a match. What you want to do is assert start and end of subject, e.g.,

echo preg_match('/^[A-Za-z]{3,5}$/', "JohnSmith") . "<br>";

xbuilder

Thanks. I guess that I was confused with the following 2. But I am clear now.

print preg_match("/^{[A-Z]{1,5}99/",} "FINGERS99")." "; // no match
print preg_match("/^{[A-Z]{1,5}/",} "FINGERS99")." "; // match

Now another QUESTION:

print preg_match("/^{\$[A-Za-z]+/",} "$First")." "; // no match
print preg_match("/^\$[A-Za-z]*/", "$First")." "; // match

Why the first line does not have a match??

Thanks
XB

laserlight

Why the first line does not have a match??

It might have a match, it depends on what is the contents of $First.

I suggest you use single quote delimited strings for your regular expression patterns. With double quote delimited strings you have to escape special characters, and this obfuscates the regex pattern.

xbuilder

Well, it is interesting that I have noticed the following:

the first in the pattern (first parameter), I must escape $ even I though I used single quotes
in the string value (second parameter), I must NOT escape $ even though I used single quotes

I can remember the above finding but can't understand make sense of it.

Note that the $First in the following is quoted, i.e., I am not using the value of the variable, rather, I used string "$First".

print preg_match('/^{\$[A-Za-z]+/',} "$First")." "; // match
print preg_match('/^\$[A-Za-z]/', "$First")." "; // match
print preg_match('/^{\$[A-Za-z]+/',} "\$First")." "; // match
print preg_match('/^\$[A-Za-z]/', "\$First")." "; // match
print preg_match('/^{\$[A-Za-z]+/',} '$First')." "; // match
print preg_match('/^\$[A-Za-z]/', '$First')." "; // match
print preg_match('/^{\$[A-Za-z]+/',} '$First')." "; // match
print preg_match('/^\$[A-Za-z]/', '$First')." "; // match
print preg_match('/^{\$[A-Za-z]+/',} '\$First')." "; // NO match
print preg_match('/^\$[A-Za-z]*/', '\$First')." "; // NO match

laserlight

- the first in the pattern (first parameter), I must escape $ even I though I used single quotes

That's correct, since you want a literal '$', but $ has meaning in regex (assert end of subject, or line). The escaping is for the regex, not the PHP string.

- in the string value (second parameter), I must NOT escape $ even though I used single quotes

That's correct, since such escaping pertains to the PHP string, but $ has no meaning in single quote delimited PHP strings other than as a literal '$'.

Note that the $First in the following is quoted, i.e., I am not using the value of the variable, rather, I used string "$First".

"$First" is equivalent to (string)$First (i.e., the variable $First cast to string). This means that you are using the value of the variable $First. Use single quotes, or "\$First" if you do not want this behaviour (variable interpolation).

xbuilder

Great. Thanks.

I didn't know "$First" uses the variable value for function parameters. I though it would use the literal string. This is such different from C/C++.

NogDog

It's just like Perl, though, if that helps any. 🙂

xbuilder

It does help me change the mentality!!