5.8 Checking Characters

You want to check whether a value contains only alphabetic characters.

Technique

Use eregi () in conjunction with character classes:

 <?php if (eregi ("^[a-z]+$", $line)) {     // .. do if true } else {     // .. do if false } ?>

Or use the predefined character class along with ereg() :

 <?php if (ereg ("^[[:alpha:]]+$", $line)) {     // .. do if true } else {     // .. do if false } ?>

Comments

In the first solution, we use eregi() , which performs a case-insensitive query using a specified pattern (in this case, [a-z] ). As discussed in the introduction, the regular expression [a-z] is a character class that will match any lowercase letter from a to z. Because we are using a case-insensitive search, [a-z] will match any character. We put a plus after the [a-z] character class to indicate that there must be one or more occurrences. The entire regular expression is enclosed within ^ and $ , meaning that the entire string must match the pattern (this is also discussed in the introduction).

In the second solution, we simply substitute eregi() (case-insensitive) with ereg() (case-sensitive), and instead of [a-z] we use [[:alpha:]] which is a predefined character set that matches any alphabetic character. PHP provides several of these predefined character classes, listed in the following table.

Name	Description
`[[:alnum:]]`	All alphanumeric characters `[a-zA-Z0-9]`
`[[:alpha:]]`	All alphabetic characters `[a-z]`
`[[:blank:]]`	Tab and space `[\t ]`
`[[:cntrl:]]`	All the control characters
`[[:digit:]]`	All decimal digits `[0-9]`
`[[:graph:]]`	All printable characters except space
`[[:lower:]]`	All lowercase letters `[a-z]`
`[[:print:]]`	All printable characters
`[[:punct:]]`	Punctuation marks `[\.,;:-]`
`[[:space:]]`	All whitespace characters
`[[:upper:]]`	All the uppercase letters `[A-Z]`
`[[:xdigit:]]`	The set of hexadecimal digits

These are just easy ways to access commonly used character classes. To negate reserved classes, make sure that you put the ^ inside the first bracket :

 [^[:space:]] // Match anything that isn't a space