I imagine I need to remove chars 0-31 and 127,
Is there a function or piece of code to do this efficiently.
If your Tardis just landed in 1963, and you just want the 7 bit printable ASCII chars, you can rip out everything from 0-31 and 127-255 with this:
$string = preg_replace('/[\x00-\x1F\x7F-\xFF]/', '', $string);
It matches anything in range 0-31, 127-255 and removes it.
You fell into a Hot Tub Time Machine, and you're back in the eighties. If you've got some form of 8 bit ASCII, then you might want to keep the chars in range 128-255. An easy adjustment - just look for 0-31 and 127
$string = preg_replace('/[\x00-\x1F\x7F]/', '', $string);
Ah, welcome back to the 21st century. If you have a UTF-8 encoded string, then the
/u modifier can be used on the regex
$string = preg_replace('/[\x00-\x1F\x7F]/u', '', $string);
This just removes 0-31 and 127. This works in ASCII and UTF-8 because both share the same control set range (as noted by mgutt below). Strictly speaking, this would work without the
/u modifier. But it makes life easier if you want to remove other chars...
In a UTF-8 string, this would be encoded as
0xC2A0. You could look for and remove that specific sequence, but with the
/u modifier in place, you can simply add
\xA0 to the character class:
$string = preg_replace('/[\x00-\x1F\x7F\xA0]/u', '', $string);
preg_replace is pretty efficient, but if you're doing this operation a lot, you could build an array of chars you want to remove, and use str_replace as noted by mgutt below, e.g.
//build an array we can re-use across several operations $badchar=array( // control characters chr(0), chr(1), chr(2), chr(3), chr(4), chr(5), chr(6), chr(7), chr(8), chr(9), chr(10), chr(11), chr(12), chr(13), chr(14), chr(15), chr(16), chr(17), chr(18), chr(19), chr(20), chr(21), chr(22), chr(23), chr(24), chr(25), chr(26), chr(27), chr(28), chr(29), chr(30), chr(31), // non-printing characters chr(127) ); //replace the unwanted chars $str2 = str_replace($badchar, '', $str);
Intuitively, this seems like it would be fast, but it's not always the case, you should definitely benchmark to see if it saves you anything. I did some benchmarks across a variety string lengths with random data, and this pattern emerged using php 7.0.12
2 chars str_replace 5.3439ms preg_replace 2.9919ms preg_replace is 44.01% faster 4 chars str_replace 6.0701ms preg_replace 1.4119ms preg_replace is 76.74% faster 8 chars str_replace 5.8119ms preg_replace 2.0721ms preg_replace is 64.35% faster 16 chars str_replace 6.0401ms preg_replace 2.1980ms preg_replace is 63.61% faster 32 chars str_replace 6.0320ms preg_replace 2.6770ms preg_replace is 55.62% faster 64 chars str_replace 7.4198ms preg_replace 4.4160ms preg_replace is 40.48% faster 128 chars str_replace 12.7239ms preg_replace 7.5412ms preg_replace is 40.73% faster 256 chars str_replace 19.8820ms preg_replace 17.1330ms preg_replace is 13.83% faster 512 chars str_replace 34.3399ms preg_replace 34.0221ms preg_replace is 0.93% faster 1024 chars str_replace 57.1141ms preg_replace 67.0300ms str_replace is 14.79% faster 2048 chars str_replace 94.7111ms preg_replace 123.3189ms str_replace is 23.20% faster 4096 chars str_replace 227.7029ms preg_replace 258.3771ms str_replace is 11.87% faster 8192 chars str_replace 506.3410ms preg_replace 555.6269ms str_replace is 8.87% faster 16384 chars str_replace 1116.8811ms preg_replace 1098.0589ms preg_replace is 1.69% faster 32768 chars str_replace 2299.3128ms preg_replace 2222.8632ms preg_replace is 3.32% faster
The timings themselves are for 10000 iterations, but what's more interesting is the relative differences. Up to 512 chars, I was seeing preg_replace alway win. In the 1-8kb range, str_replace had a marginal edge.
I thought it was interesting result, so including it here. The important thing is not to take this result and use it to decide which method to use, but to benchmark against your own data and then decide.
Many of the other answers here do not take into account unicode characters (e.g. öäüßйȝîûηыეமிᚉ⠛ ). In this case you can use the following:
$string = preg_replace('/[\x00-\x08\x0B\x0C\x0E-\x1F\x7F-\x9F]/u', '', $string);
There's a strange class of characters in the range
\x80-\x9F (Just above the 7-bit ASCII range of characters) that are technically control characters, but over time have been misused for printable characters. If you don't have any problems with these, then you can use:
$string = preg_replace('/[\x00-\x08\x0B\x0C\x0E-\x1F\x7F]/u', '', $string);
If you wish to also strip line feeds, carriage returns, tabs, non-breaking spaces, and soft-hyphens, you can use:
$string = preg_replace('/[\x00-\x1F\x7F-\xA0\xAD]/u', '', $string);
Note that you must use single quotes for the above examples.
If you wish to strip everything except basic printable ASCII characters (all the example characters above will be stripped) you can use:
$string = preg_replace( '/[^[:print:]]/', '',$string);
For reference see http://www.fileformat.info/info/charset/UTF-8/list.htm