What does this mean?

condoug

Could someone explain what this does to the credit card number variable?

!preg_match('/[0-9]{1,20}/',$creditcard);

Many Thanks

laserlight

Nothing.

Read the PHP Manual on [man]preg_match/man for more details.

condoug

Nothing?

Surely if it did nothing it would fail and echo an error to screen?

I think its supposed to check the the variable contains only number but Im unsure as to what the section with curly braces does.

Any suggestions?

laserlight

Nothing?

Surely if it did nothing it would fail and echo an error to screen?

Oh, it does something, of course, but it does not change $creditcard in any way. It merely returns an integer (0 or 1) depending on whether the pattern matched the value in $creditcard.

I think its supposed to check the the variable contains only number but Im unsure as to what the section with curly braces does.

It checks if $creditcard has 1 to 20 consecutive digits. It does not check if $creditcard only has digits since it does not assert the start and end of the subject.

greensweater

it returns true or false (negated by the !). In the regular expression, [0-9] means match any digit, and {1,20} means between one and twenty of the previous expression. Not a very good credit card validator IMO 🙂

condoug

Thanks for the input.

However, if all it is doing is checking the number is 'numeric' and checking it's length, how can this be improved in a single line of code?

I obviously have not posted the rest of the credit card validation script so this is not just it!! 🙂

Thanks again

laserlight

However, if all it is doing is checking the number is 'numeric' and checking it's length, how can this be improved in a single line of code?

I repeat: it does not check if the subject is numeric. It checks if the subject contains numeric elements. As for improvement: that depends on what you want to do. For example, if you want to check if $creditcard has 1 to 20 digits only, you might write:

if (preg_match('/^\d{1,20}$/', $creditcard)) {
    // Credit card number has 1 to 20 digits only.
    // ...
}

greensweater

!preg_match("/^[0-9]{13-16}$/",$creditcard);

This will at least match properly formatted visa/mc/disc, amex and others. I know of no CC's that aren't 13-16 digits long. Use a Luhn algorithm to check valid numbers.