preg_replace() not working for repeating words

Question

I would like to replace each occurence of hello with bye in a sentence or paragraph.

$sentence = 'nothello hello hello hello hello hello';
$find = 'hello';
$replace = 'bye';
$str = preg_replace('/(^|[\s])'.$find.'([\s]|$)/', '$1'.$replace.'$2', $sentence);

echo $str;

I want this to echo nothello bye bye bye bye bye but instead I get nothello bye hello bye hello bye.

What am I doing wrong?

I can't use \b because I am using lots of languages.

*Edit I guess \b can work if you use the u flag.

Here use `str_replace` instead of `preg_replace` try this https://eval.in/792387 — Sahil Gulati, May 11 '17 at 17:39
You can use `\b` because once you use the unicode `u` modifier, `\b` becomes Unicode-aware and will match Unicode word boundaries. — Wiktor Stribiżew, May 11 '17 at 18:02
`preg_replace('/\b'.$find.'\b/u', $replace, $sentence);` should work. It is said to work as of PHP 5.3.4 — Wiktor Stribiżew, May 11 '17 at 18:24

score 2 · Accepted Answer · answered May 11 '17 at 17:44

This the right place to use zero-length assertions called lookahead and lookbehind instead of matching:

$str = preg_replace('/(?<=^|\s)'.$find.'(?=\s|$)/', $replace, $sentence);
//=> bye bye bye bye bye

More on lookarounds in regex

(?=...) is positive lookahead and (?<=...) is positive lookbehind.

score 0 · Answer 2 · answered May 11 '17 at 17:49

You current regex search translate into this:

(^|[\s])hello([\s]|$)

which will match a string start with "hello " -- which match the first hello. or the string " hello " or end with " hello" (a white space before the hello) which will match the 3rd and the last.

if don't need regex search/replace use str_replace as suggested before. If you need to use regex, use a regex test tool/site like https://regex101.com/ to test your regex more closely.

score 0 · Answer 3 · answered May 11 '17 at 17:58

0

$sentence = 'nothello hello hello hello hello hello';
$find = 'hello';
$replace = 'bye';
$str = preg_replace('/(^|[\s])'.$find.'([\s]#i|$)/', '$1'.$replace.'$2', $sentence);

echo $str;

you need the "#i" to replace it through the whole string

answered May 11 '17 at 17:58

User__42

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preg_replace() not working for repeating words

3 Answers3