คนเขียนเว็บด้วย PHP, Javascript ชอบสิ่งนี้
การหาอีเมล์ในข้อความจำเป็นต้องสร้างประโยค Regular Expression เช่น "[/^[a-zA-Z0-9._-]+@[a-zA-Z0-9-]+\.[a-zA-Z.]{2,5}$/]"
| Metacharacter | Description | Example |
|---|---|---|
| . | Matches any single character except a new line | /./ matches anything that has a single character |
| ^ | Matches the beginning of or string / excludes characters | /^PH/ matches any string that starts with PH |
| $ | Matches pattern at the end of the string | /com$/ matches guru99.com,yahoo.com Etc. |
| * | Matches any zero (0) or more characters | /com*/ matches computer, communication etc. |
| + | Requires preceding character(s) appear at least once | /yah+oo/ matches yahoo |
| \ | Used to escape meta characters | /yahoo+\.com/ treats the dot as a literal value |
| [...] | Character class | /[abc]/ matches abc |
| a-z | Matches lower case letters | /a-z/ matches cool, happy etc. |
| A-Z | Matches upper case letters | /A-Z/ matches WHAT, HOW, WHY etc. |
| 0-9 | Matches any number between 0 and 9 | /0-4/ matches 0,1,2,3,4 |
The above list only gives the most commonly used metacharacters in regular expressions.
Let’s now look at a fairly complex example that checks the validity of an email address.
<?php
$my_email = "name@company.com";
if (preg_match("/^[a-zA-Z0-9._-]+@[a-zA-Z0-9-]+\.[a-zA-Z.]{2,5}$/", $my_email)) {
echo "$my_email is a valid email address";
}
else
{
echo "$my_email is NOT a valid email address";
}
?>
Explaining the pattern
HERE,
- "'/.../'" starts and ends the regular expression
- "^[a-zA-Z0-9._-]" matches any lower or upper case letters, numbers between 0 and 9 and dots, underscores or dashes.
- "+@[a-zA-Z0-9-]" matches the @ symbol followed by lower or upper case letters, numbers between 0 and 9 or dashes.
- "+\.[a-zA-Z.]{2,5}$/" escapes the dot using the backslash then matches any lower or upper case letters with a character length between 2 and 5 at the end of the string.
