How to detect if a string has only letters in php

In php, you can use the preg_match() function with the regular expression "/^[a-zA-Z\s] $/" to detect whether a string has only letters. The syntax "preg_match("/^[a -zA-Z\s] $/",string)"; if the return value is 1, only letters are returned, if 0 is returned, other characters are included.

The operating environment of this tutorial: windows7 system, PHP7.1 version, DELL G3 computer

php detects whether the string only has letters, in other words That is: Determine whether the string is pure English letters

In PHP, you can use the preg_match() function with a regular expression to check.

Regular expression used: "/^[a-zA-Z\s] $/"

## The #preg_match() function can search and match strings based on regular expressions. The syntax format of the function is as follows:

preg_match($pattern,$subject [, &$matches [, $flags = 0 [, $offset = 0 ]]])

The parameter description is as follows:

$pattern: the pattern to be searched , which is the edited regular expression;
• $subject: the string to be searched;
• $matches: optional parameters (array type), if $matches is provided, it will is populated as search results. $matches[0] contains the text matched by the complete pattern, $matches[1] contains the text matched by the first capture subgroup, and so on;
• $flags: optional parameter, $flags can Is set to PREG_OFFSET_CAPTURE. If this tag is passed, for each occurrence of a match, the string offset (relative to the target string) will be appended to the return;
• $offset: optional parameter, Used to specify where to start searching in the target string (unit is bytes).

preg_match() function can return the number of matches for $pattern. Its value will be 0 times (no match) or 1 time, because preg_match() will stop searching after the first match. .

If the return value is 1, it contains only letters, and if the return value is 0, it contains other characters.

Example:

<?php
header(&#39;content-type:text/html;charset=utf-8&#39;);  
echo preg_match("/^[a-zA-Z\s]+$/","abcddfkj")."<br>";
echo preg_match("/^[a-zA-Z\s]+$/","ab12kj");
?>

This kind of output is not very good. Let’s customize a function and do a process to return true if there are only letters. Otherwise return false

function is_english($str)
{
    if(preg_match("/^[a-zA-Z\s]+$/",$str)){
        return true;
    }
    return false;
}

Call the function to determine whether the string is composed of pure English letters

var_dump(is_english('php.cn')); 
// bool(false)   含有标点符号所以返回 false  
var_dump(is_english('phpcn'));  
// bool(true)
var_dump(is_english('phpcn123')); 
// bool(false)   含有123
var_dump(is_english('欢迎来到这里')); 
// bool(false)   都是中文

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