Replace strings differently depending if is enclosed in braces or not

I want to replace all instances of an specific words between braces with something else, unless it is written between double braces, 开发者_如何学Gowhile it should show as is it was written with single braces without the filter. I have tried a code but only works for the first match. The rest are shown depending of the first one:

$foo = 'a {bar} b {{bar}} c {bar} d';
$baz = 'Chile';
preg_match_all( '/(\{?)\{(tin)\}(\}?)/i', $foo, $matches, PREG_SET_ORDER );
    if ( !empty($matches) ) {
        foreach ( (array) $matches as $match ) {
            if( empty($match[1]) && empty($match[3])) {
                $tull = str_replace( $match[0], $baz, $foo );
            } else {
                $tull = str_replace( $match[0], substr($match[0], 1, -1), $foo ) ;
            }
        }
    } 
    echo $tull;

EDIT: use case:

If I write:

"Write {{bar}} to output the template. Example: I want to go to {bar}."

I want to have:

"Write {bar} to output the template. Example: I want to go to CHILE."

You could use two regular expressions, one to look for the double-braced items and another for the single-braced ones. Alternatively, a callback could be used to determine the replacement value with just one regular expression.

Separate patterns

$subject = 'Write {{bar}} to output the template. Example: I want to go to {bar}.';
$replacement = 'CHILE';
echo preg_replace(
    array('/(?<!\{)\{bar\}(?!\})/', '/\{\{bar\}\}/'),
    array($replacement, '{bar}'),
    $subject
);

Single pattern with callback

echo preg_replace_callback(
    '/(\{)?(\{bar\})(?(1)\})/',
    function ($match) use ($replacement) {
        if ($match[0][1] === '{') {
            return $match[2];
        }
        return $replacement;
    },
    $subject
);

Finally, are you doing this for one hard-coded labels (always bar) or will the label part be a key for some varying replacement string?

You can't do this in a single regex. First use

(?<!\{)\{bar\}(?!\})

to match {bar} only if there are no further braces around it. I.e.

preg_replace('/(?<!\{)\{bar\}(?!\})/m', 'CHILE', 'Write {{bar}} to output the template. Example: I want to go to {bar}.');

will return

Write {{bar}} to output the template. Example: I want to go to CHILE.

Then do a normal search-and-replace to replace {{ with { and }} with }.