Regular Expression to match unlimited number of options

Question

I want to be able to parse file paths like this one:

 /var/www/index.(htm|html|php|shtml)

into an ordered array:

 array("htm", "html", "php", "shtml")

and then produce a list of alternatives:

/var/www/index.htm
/var/www/index.html
/var/www/index.php
/var/www/index.shtml

Right now, I have a preg_match statement that can split two alternatives:

 preg_match_all ("/\(([^)]*)\|([^)]*)\)/", $path_resource, $matches);

Could somebody give me a pointer how to extend this to accept an unlimited number of alternatives (at least two)? Just regarding the regular expression, the rest I can deal with.

The rule is:

• The list needs to start with a ( and close with a )

• There must be one | in the list (i.e. at least two alternatives)

• Any other occurrence(s) of ( or ) are to remain untouched.

Update: I need to be able to also deal with multiple bracket pairs such as:

 /var/(www|www2)/index.(htm|html|php|shtml)

sorry I didn't say that straight away.

Update 2: If you're looking to do what I'm trying to do in the filesystem, then note that glob() already brings this functionality out of the box. There is no need to implement a custom solutiom. See @Gordon's answer below for details.

Answer 1

Non-regex solution :)

<?php

$test = '/var/www/index.(htm|html|php|shtml)';

/**
 *
 * @param string $str "/var/www/index.(htm|html|php|shtml)"
 * @return array "/var/www/index.htm", "/var/www/index.php", etc
 */
function expand_bracket_pair($str)
{
    // Only get the very last "(" and ignore all others.
    $bracketStartPos = strrpos($str, '(');
    $bracketEndPos = strrpos($str, ')');

    // Split on ",".
    $exts = substr($str, $bracketStartPos, $bracketEndPos - $bracketStartPos);
    $exts = trim($exts, '()|');
    $exts = explode('|', $exts);

    // List all possible file names.
    $names = array();

    $prefix = substr($str, 0, $bracketStartPos);
    $affix = substr($str, $bracketEndPos + 1);
    foreach ($exts as $ext)
    {
        $names[] = "{$prefix}{$ext}{$affix}";
    }

    return $names;
}

function expand_filenames($input)
{
    $nbBrackets = substr_count($input, '(');

    // Start with the last pair.
    $sets = expand_bracket_pair($input);

    // Now work backwards and recurse for each generated filename set.
    for ($i = 0; $i < $nbBrackets; $i++)
    {
        foreach ($sets as $k => $set)
        {
            $sets = array_merge(
                $sets,
                expand_bracket_pair($set)
            );
        }
    }

    // Clean up.
    foreach ($sets as $k => $set)
    {
        if (false !== strpos($set, '('))
        {
            unset($sets[$k]);
        }
    }
    $sets = array_unique($sets);
    sort($sets);

    return $sets;
}

var_dump(expand_filenames('/(a|b)/var/(www|www2)/index.(htm|html|php|shtml)'));

Answer 2

I think you're looking for:

/(([^|]+)(|([^|]+))+)/

Basically, put the splitter '|' into a repeating pattern.

Also, your words should be made up 'not pipes' instead of 'not parens', per your third requirement.

Also, prefer + to * for this problem. + means 'at least one'. * means 'zero or more'.

Answer 3

Not exactly what you are asking, but what's wrong with just taking what you have to get the list (ignoring the |s), putting it into a variable and then explodeing on the |s? That would give you an array of however many items there were (including 1 if there wasn't a | present).

Answer 4

Maybe I'm still not getting the question, but my assumption is you are running through the filesystem until you hit one of the files, in which case you could do

$files = glob("$path/index.{htm,html,php,shtml}", GLOB_BRACE);

The resulting array will contain any file matching your extensions in $path or none. If you need to include files by a specific extension order, you can foreach over the array with an ordered list of extensions, e.g.

foreach(array('htm','html','php','shtml') as $ext) {
    foreach($files as $file) {
        if(pathinfo($file, PATHINFO_EXTENSION) === $ext) {
            // do something
        }
    }
}

Edit: and yes, you can have multiple curly braces in glob.

Answer 5

The answer is given, but it's a funny puzzle and i just couldn't resist

function expand_filenames2($str) {
    $r = array($str);
    $n = 0;
    while(preg_match('~(.*?) \( ( \w+ \| [\w|]+ ) \) (.*) ~x', $r[$n++], $m)) {
        foreach(explode('|', $m[2]) as $e)
            $r[] = $m[1] . $e . $m[3];
    }
    return array_slice($r, $n - 1);
}  



print_r(expand_filenames2('/(a|b)/var/(ignore)/(www|www2)/index.(htm|html|php|shtml)!'));

maybe this explains a bit why we like regexps that much ;)