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I am trying to replace occurances of whole words in a string. There are similar questions here at SO like this and this.

Answers to all these questions recommend using regex like this:

$needle = "a";
$haystack = "oh my dear a";
$haystack = preg_replace("/$needle\b/", 'God', $haystack);
echo $haystack;

This works good for whole words - echoes oh my dear God

But if I replace a with a. in both needle and haystack, i;e

$needle = "a.";
$haystack = "oh my dear a.";

the output becomes oh my deGod a. because . gets evaluated as regex.

I would want a. to be replaced by God with or without regex.

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bhaskarc
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2 Answers2

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\b refers only to word boundaries in an ASCII perception. Also . is a character of special meaning in regular expression — meaning "match any single character (except newline)"

If the "needle" may contain special characters, use preg_quote() and create DIY boundaries.

preg_quote() takes str and puts a backslash in front of every character that is part of the regular expression syntax. This is useful if you have a run-time string that you need to match in some text and the string may contain special regex characters.

$str = preg_replace("~(?<=^| )" . preg_quote($needle, "~") . "(?= |$)~", 'God', $str);
hwnd
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Maybe this will give you an inspiration...

$haystack="oh my dear a." ;
$needle="a" ;
$hout=$haystack ;
$hout=~ s/\b$needle\b\./God/g ;

print "$haystack $needle $hout\n";

...produces this output...

oh my dear a. a oh my dear God

This works in perl. Sorry, my php is way rusty.

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