I imagine I need to remove chars 0-31 and 127,
Is there a function or piece of code to do this efficiently.
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问题:
回答1:
7 bit ASCII?
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.
8 bit extended ASCII?
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);
UTF-8?
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...
If you\'re dealing with Unicode, there are potentially many non-printing elements, but let\'s consider a simple one: NO-BREAK SPACE (U+00A0)
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);
Addendum: What about str_replace?
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.
回答2:
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
回答3:
you can use character classes
/[[:cntrl:]]+/
回答4:
Starting with PHP 5.2, we also have access to filter_var, which I have not seen any mention of so thought I\'d throw it out there. To use filter_var to strip non-printable characters < 32 and > 127, you can do:
Filter ASCII characters below 32
$string = filter_var($input, FILTER_UNSAFE_RAW, FILTER_FLAG_STRIP_LOW);
Filter ASCII characters above 127
$string = filter_var($input, FILTER_UNSAFE_RAW, FILTER_FLAG_STRIP_HIGH);
Strip both:
$string = filter_var($input, FILTER_UNSAFE_RAW, FILTER_FLAG_STRIP_LOW|FILTER_FLAG_STRIP_HIGH);
You can also html-encode low characters (newline, tab, etc.) while stripping high:
$string = filter_var($input, FILTER_UNSAFE_RAW, FILTER_FLAG_ENCODE_LOW|FILTER_FLAG_STRIP_HIGH);
There are also options for stripping HTML, sanitizing e-mails and URLs, etc. So, lots of options for sanitization (strip out data) and even validation (return false if not valid rather than silently stripping).
Sanitization: http://php.net/manual/en/filter.filters.sanitize.php
Validation: http://php.net/manual/en/filter.filters.validate.php
However, there is still the problem, that the FILTER_FLAG_STRIP_LOW will strip out newline and carriage returns, which for a textarea are completely valid characters...so some of the Regex answers, I guess, are still necessary at times, e.g. after reviewing this thread, I plan to do this for textareas:
$string = preg_replace( \'/[^[:print:]\\r\\n]/\', \'\',$input);
This seems more readable than a number of the regexes that stripped out by numeric range.
回答5:
this is simpler:
$string = preg_replace( \'/[^[:cntrl:]]/\', \'\',$string);
回答6:
All of the solutions work partially, and even below probably does not cover all of the cases. My issue was in trying to insert a string into a utf8 mysql table. The string (and its bytes) all conformed to utf8, but had several bad sequences. I assume that most of them were control or formatting.
function clean_string($string) {
$s = trim($string);
$s = iconv(\"UTF-8\", \"UTF-8//IGNORE\", $s); // drop all non utf-8 characters
// this is some bad utf-8 byte sequence that makes mysql complain - control and formatting i think
$s = preg_replace(\'/(?>[\\x00-\\x1F]|\\xC2[\\x80-\\x9F]|\\xE2[\\x80-\\x8F]{2}|\\xE2\\x80[\\xA4-\\xA8]|\\xE2\\x81[\\x9F-\\xAF])/\', \' \', $s);
$s = preg_replace(\'/\\s+/\', \' \', $s); // reduce all multiple whitespace to a single space
return $s;
}
To further exacerbate the problem is the table vs. server vs. connection vs. rendering of the content, as talked about a little here
回答7:
My UTF-8 compliant version:
preg_replace(\'/[^\\p{L}\\s]/u\',\'\',$value);
回答8:
You could use a regular express to remove everything apart from those characters you wish to keep:
$string=preg_replace(\'/[^A-Za-z0-9 _\\-\\+\\&]/\',\'\',$string);
Replaces everything that is not (^) the letters A-Z or a-z, the numbers 0-9, space, underscore, hypen, plus and ampersand - with nothing (i.e. remove it).
回答9:
preg_replace(\'/(?!\\n)[\\p{Cc}]/\', \'\', $response);
This will remove all the control characters (http://uk.php.net/manual/en/regexp.reference.unicode.php) leaving the \\n newline characters. From my experience, the control characters are the ones that most often cause the printing issues.
回答10:
The answer of @PaulDixon is completely wrong, because it removes the printable extended ASCII characters 128-255! has been partially corrected. I don\'t know why he still wants to delete 128-255 from a 127 chars 7-bit ASCII set as it does not have the extended ASCII characters.
But finally it was important not to delete 128-255 because for example chr(128) (\\x80) is the euro sign in 8-bit ASCII and many UTF-8 fonts in Windows display a euro sign and Android regarding my own test.
And it will kill many UTF-8 characters if you remove the ASCII chars 128-255 from an UTF-8 string (probably the starting bytes of a multi-byte UTF-8 character). So don\'t do that! They are completely legal characters in all currently used file systems. The only reserved range is 0-31.
Instead use this to delete the non-printable characters 0-31 and 127:
$string = preg_replace(\'/[\\x00-\\x1F\\x7F]/\', \'\', $string);
It works in ASCII and UTF-8 because both share the same control set range.
The fastest slower¹ alternative without using regular expressions:
$string = str_replace(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)
), \'\', $string);
If you want to keep all whitespace characters \\t, \\n and \\r, then remove chr(9), chr(10) and chr(13) from this list. Note: The usual whitespace is chr(32) so it stays in the result. Decide yourself if you want to remove non-breaking space chr(160) as it can cause problems.
¹ Tested by @PaulDixon and verified by myself.
回答11:
how about:
return preg_replace(\"/[^a-zA-Z0-9`_.,;@#%~\'\\\"\\+\\*\\?\\[\\^\\]\\$\\(\\)\\{\\}\\=\\!\\<\\>\\|\\:\\-\\s\\\\\\\\]+/\", \"\", $data);
gives me complete control of what I want to include
回答12:
Marked anwser is perfect but it misses character 127(DEL) which is also a non-printable character
my answer would be
$string = preg_replace(\'/[\\x00-\\x1F\\x7f-\\xFF]/\', \'\', $string);
回答13:
\"cedivad\" solved the issue for me with persistent result of Swedish chars ÅÄÖ.
$text = preg_replace( \'/[^\\p{L}\\s]/u\', \'\', $text );
Thanks!
回答14:
For anyone that is still looking how to do this without removing the non-printable characters, but rather escaping them, I made this to help out. Feel free to improve it! Characters are escaped to \\\\x[A-F0-9][A-F0-9].
Call like so:
$escaped = EscapeNonASCII($string);
$unescaped = UnescapeNonASCII($string);
<?php
function EscapeNonASCII($string) //Convert string to hex, replace non-printable chars with escaped hex
{
$hexbytes = strtoupper(bin2hex($string));
$i = 0;
while ($i < strlen($hexbytes))
{
$hexpair = substr($hexbytes, $i, 2);
$decimal = hexdec($hexpair);
if ($decimal < 32 || $decimal > 126)
{
$top = substr($hexbytes, 0, $i);
$escaped = EscapeHex($hexpair);
$bottom = substr($hexbytes, $i + 2);
$hexbytes = $top . $escaped . $bottom;
$i += 8;
}
$i += 2;
}
$string = hex2bin($hexbytes);
return $string;
}
function EscapeHex($string) //Helper function for EscapeNonASCII()
{
$x = \"5C5C78\"; //\\x
$topnibble = bin2hex($string[0]); //Convert top nibble to hex
$bottomnibble = bin2hex($string[1]); //Convert bottom nibble to hex
$escaped = $x . $topnibble . $bottomnibble; //Concatenate escape sequence \"\\x\" with top and bottom nibble
return $escaped;
}
function UnescapeNonASCII($string) //Convert string to hex, replace escaped hex with actual hex.
{
$stringtohex = bin2hex($string);
$stringtohex = preg_replace_callback(\'/5c5c78([a-fA-F0-9]{4})/\', function ($m) {
return hex2bin($m[1]);
}, $stringtohex);
return hex2bin(strtoupper($stringtohex));
}
?>
回答15:
I solved problem for UTF8 using https://github.com/neitanod/forceutf8
use ForceUTF8\\Encoding;
$string = Encoding::fixUTF8($string);
回答16:
This worked for me. I had to convert a string of any kind which was a random title in to a slug for SEO.
function string2Slug($str){
$str = trim($str);
$str = str_replace(\" \",\"_\",$str);
$temp = explode(\"\\\\u\",$str);
$str = \'\';
foreach ($temp as $bit) {
$str .= substr($bit,4);
}
$str = str_replace(\"\'\",\"\",$str);
$str = str_replace(\"\\\"\",\"\",$str);
$str = str_replace(\"\\\\\",\"\",$str);
$str = str_replace(\"\\/\",\"\",$str);
$str = str_replace(\"/\",\"\",$str);
$str = str_replace(\"?\",\"\",$str);
$str = str_replace(\"#\",\"\",$str);
$str = str_replace(\"&\",\"\",$str);
$str = str_replace(\"%\",\"\",$str);
$str = str_replace(\"!\",\"\",$str);
return $str;
}
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