[SOLVED] Is this the best way to do it?

[micah1701]

I'm new to writing my own regex statement (I've always relied on the kindness of strangers) but today I needed to find a way to validate international Amateur radio callsigns. exciting huh?

 

This is basically what I have ( i tried to explain the criteria a bit in the code itself)

<?php

/* a callsign basically has three parts:
    1) alpha-numeric prefix which could be one of these combinations...
   A-Z{1,3}               // between one and three letters
   [A-Z][0-9]             // one letter followed by one number
   [A-Z][0-9][A-Z]     // one letter, one number, one letter
   [0-9]([A-Z]{1,3})   // one number followed by between one and three letters

    2) a single number: [0-9]

    3) followed by between one and three letters: [A-Z]{1,3}
*/

function validate_callsign($callsign){
$regex = "[0-9]?"; // first character of prefix MAY be a number (but usually isn't)
$regex.= "[A-Z]{1,2}"; // Must start with 1 or 2 Letters
$regex.= "[0-9]"; //followed by 1 number
$regex.= "[A-Z][0-9]?"; //there MAY be a char and number here IF the 2nd charecter of the prefix was a number
$regex.= "[A-Z]{1,3}"; //and 1 to 3 more letters

  if(preg_match("/".$regex."/i",$callsign) ){
   return true;
  }
}

 

valid callsigns could include:

A1A

AA1A

AAA1AAA

A1A1A

1A1A

1AA1AA

 

It seems to be working as it should however i'm a little concerned about that 2nd to last line of the $regex statement: $regex.= "[A-Z][0-9]?";

 

Any thoughts from an expert?

[obsidian]

As it is, you seem to have the basic logic down, but you're not anchoring your string, so if one were to start with "***" and then a valid call sign, your pattern would match. Remember that when you need an exact match, you should start your match with "^" and end it with "$":

$pattern = '/^(\d?[a-z]{1,3}|[a-z]\d[a-z]?)\d[a-z]{1,3}$/';

 

Hope that helps some.

[effigy]

The multi-line comments seem to disagree with the pattern. Which is correct?

[micah1701]

The multi-line comments seem to disagree with the pattern. Which is correct?

 

the comments are what it SHOULD be doing.

 

the function is what I'm not sure about.  thanks :-)

[micah1701]

As it is, you seem to have the basic logic down, but you're not anchoring your string, so if one were to start with "***" and then a valid call sign, your pattern would match. Remember that when you need an exact match, you should start your match with "^" and end it with "$":

$pattern = '/^(\d?[a-z]{1,3}|[a-z]\d[a-z]?)\d[a-z]{1,3}$/';

 

Hope that helps some.

 

that actually totally helped! I never understood the point of the anchors before ('cause I didn't know what anchors were).  Thanks!

 

like i said, i've been putting off learning this stuff for way to long. I can't rely on google+cut+paste forever.  Thanks for your help.

[effigy]

<pre>
<?php

$tests = array (
	'A1A',
	'AA1A', 
	'AAA1AAA',
	'A1A1A',
	'1A1A',
	'1AA1AA',
);

function validate_callsign($callsign){
	$regex = '/
		\A ### BOL
		(?:
			\d? ### Optional digit
			[A-Z]{1,3} ### 1-3 letters
			| ### OR
			[A-Z] ### 1 letter
			\d ### 1 digit
			[A-Z]? ### Optional letter
		)
		\d ### Digit
		[A-Z]{1,3} ### 1-3 letters
		\z ### EOL
	/xi';
	if (preg_match($regex, $callsign)) {
		return true;
	}
}

foreach ($tests as $test) {
	echo $test, ' -- ', (validate_callsign($test) ? 'Valid' : 'Invalid'), '<br/>';
}
?>
</pre>

[micah1701]

thanks Effigy. thats very awesome.

 

I'm assuming the colon after the question mark means mean that one of the cases must match?

 

Also, what is the reason for excaping the A at the begining?

 

Thanks again for your help, I'm so glad I'm finally beginning to wrap my head around regular expression.  (now if i could just learn spanish)

 

[laffin]

One of the best tools I have found for regular expressions is Expresso, try googl'n it

 

[effigy]

I'm assuming the colon after the question mark means mean that one of the cases must match?

(?:regex) -- Non-capturing parentheses group the regex so you can apply regex operators, but do not capture anything and do not create backreferences.

Source

 

Also, what is the reason for excaping the A at the begining?

\A -- Matches at the start of the string the regex pattern is applied to. Matches a position rather than a character. Never matches after line breaks.

Source

 

I love that image Thanks for sharing.