Asked  7 Months ago    Answers:  5   Viewed   29 times

Is there a good way of test if a string is a regex or normal string in PHP?

Ideally I want to write a function to run a string through, that returns true or false.

I had a look at preg_last_error():

<?php
preg_match('/[a-z]/', 'test');
var_dump(preg_last_error());
preg_match('invalid regex', 'test');
var_dump(preg_last_error());
?>

Where obviously first one is not an error, and second one is. But preg_last_error() returns int 0 both times.

Any ideas?

 Answers

49

The only easy way to test if a regex is valid in PHP is to use it and check if a warning is thrown.

ini_set('track_errors', 'on');
$php_errormsg = '';
@preg_match('/[blah/', '');
if($php_errormsg) echo 'regex is invalid';

However, using arbitrary user input as a regex is a bad idea. There were security holes (buffer overflow => remote code execution) in the PCRE engine before and it might be possible to create specially crafted long regexes which require lots of cpu/memory to compile/execute.

Wednesday, March 31, 2021
 
coolguy
answered 7 Months ago
72

If you do want to match umlauts, then add the regex /u modifier, or use pL in place of w. That will allow the regex to match letters outside of the ASCII range.

Reference: http://www.regular-expressions.info/unicode.html
and http://php.net/manual/en/regexp.reference.unicode.php

Saturday, May 29, 2021
 
keyBeatz
answered 5 Months ago
65

You can use:

preg_match_all("!<span[^>]+>(.*?)</span>!", $str, $matches);

Then your text will be inside the first capture group (as seen on rubular)

With that out of the way, note that regex shouldn't be used to parse HTML. You will be better off using an XML parser, unless it's something really, really simple.

Saturday, May 29, 2021
 
freeMagee
answered 5 Months ago
79

EDIT: Here is an update using the Java 8 Streaming API. So much cleaner. Can still be combined with regular expressions too.

public static boolean stringContainsItemFromList(String inputStr, String[] items) {
    return Arrays.stream(items).anyMatch(inputStr::contains);
}

Also, if we change the input type to a List instead of an array we can use items.stream().anyMatch(inputStr::contains).

You can also use .filter(inputStr::contains).findAny() if you wish to return the matching string.

Important: the above code can be done using parallelStream() but most of the time this will actually hinder performance. See this question for more details on parallel streaming.


Original slightly dated answer:

Here is a (VERY BASIC) static method. Note that it is case sensitive on the comparison strings. A primitive way to make it case insensitive would be to call toLowerCase() or toUpperCase() on both the input and test strings.

If you need to do anything more complicated than this, I would recommend looking at the Pattern and Matcher classes and learning how to do some regular expressions. Once you understand those, you can use those classes or the String.matches() helper method.

public static boolean stringContainsItemFromList(String inputStr, String[] items)
{
    for(int i =0; i < items.length; i++)
    {
        if(inputStr.contains(items[i]))
        {
            return true;
        }
    }
    return false;
}
Monday, June 7, 2021
 
Corsair
answered 5 Months ago
82

In Java Regex, there's a difference between Matcher.find() (find a match anywhere in the String) and Matcher.matches() (match the entire String).

String only has a matches() method (implemented equivalent to this code:Pattern.compile(pattern).matcher(this).matches();), so you need to create a pattern that matches the full String:

System.out.println("I end with a number 4".matches("^.*\d$"));
Friday, July 30, 2021
 
Dobz
answered 3 Months ago
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