I have the following requirements for validating an input field:
It should only contain alphabets and spaces between the alphabets.
It cannot contain spaces at the beginning or end of the string.
It cannot contain any other special character.
I am using following regex for this:
^(?!\s*$)[-a-zA-Z ]*$
But this is allowing spaces at the beginning. Any help is appreciated.
For me the only logical way to do this is:
^\p{L}+(?: \p{L}+)*$
At the start of the string there must be at least one letter. (I replaced your [a-zA-Z] by the Unicode code property for letters \p{L}). Then there can be a space followed by at least one letter, this part can be repeated.
\p{L}: any kind of letter from any language. See regular-expressions.info
The problem in your expression ^(?!\s*$) is, that lookahead will fail, if there is only whitespace till the end of the string. If you want to disallow leading whitespace, just remove the end of string anchor inside the lookahead ==> ^(?!\s)[-a-zA-Z ]*$. But this still allows the string to end with whitespace. To avoid this look back at the end of the string ^(?!\s)[-a-zA-Z ]*(?<!\s)$. But I think for this task a look around is not needed.
This should work if you use it with String.matches method. I assume you want English alphabet.
"[a-zA-Z]+(\\s+[a-zA-Z]+)*"
Note that \s will allow all kinds of whitespace characters. In Java, it would be equivalent to
[ \t\n\x0B\f\r]
Which includes horizontal tab (09), line feed (10), carriage return (13), form feed (12), backspace (08), space (32).
If you want to specifically allow only space (32):
"[a-zA-Z]+( +[a-zA-Z]+)*"
You can further optimize the regex above by making the capturing group ( +[a-zA-Z]+) non-capturing (with String.matches you are not going to be able to get the words individually anyway). It is also possible to change the quantifiers to make them possessive, since there is no point in backtracking here.
"[a-zA-Z]++(?: ++[a-zA-Z]++)*+"
Try this:
^(((?<!^)\s(?!$)|[-a-zA-Z])*)$
This expression uses negative lookahead and negative lookbehind to disallow spaces at the beginning or at the end of the string, and requiring the match of the entire string.
I think the problem is there's a ? before the negation of white spaces, which means it is optional
This should work:
[a-zA-Z]{1}([a-zA-Z\s]*[a-zA-Z]{1})?
at least one sequence of letters, then optional string with spaces but always ends with letters
I don't know if words in your accepted string can be seperated by more then one space. If they can:
^[a-zA-Z]+(( )+[a-zA-z]+)*$
If can't:
^[a-zA-Z]+( [a-zA-z]+)*$
String must start with letter (or few letters), not space.
String can contain few words, but every word beside first must have space before it.
Hope I helped.
I was using the following regex with preg_replace to filter inputs:
/[^A-Za-z0-9[:space:][:blank:]_<>=##£€$!?:;%,.\\'\\\"()&+\\/-]/
However this does not allow accented characters like umlauts so I changed it to:
/[^\w[:space:][:blank:]_<>=##$£€!?:;%,.\\'\\\"()&+\\/-]/u
This however does work with the £ or € characters, nothing is returned, but I need to accept these characters, I have tried escaping them but that doesn't work.
Also I want to create an regex that is similar to just A-Za-z but will allow accented characters, how can I do that?
From http://php.net/manual/en/reference.pcre.pattern.modifiers.php
u (PCRE_UTF8) This modifier turns on additional functionality of PCRE
that is incompatible with Perl. Pattern and subject strings are
treated as UTF-8. An invalid subject will cause the preg_* function to
match nothing; an invalid pattern will trigger an error of level
E_WARNING. Five and six octet UTF-8 sequences are regarded as invalid
since PHP 5.3.4 (resp. PCRE 7.3 2007-08-28); formerly those have been
regarded as valid UTF-8.
That means that first you have to make sure the input string is proper UTF-8 text.
Secondly, have you heard of unicode categories? If not, head to http://www.regular-expressions.info/unicode.html and search for Unicode categories. For example you could use \p{S} to match all currency symbols, or \p{L} for all letters. Your regex could (probably) be written as follows: /[^\p{L}\p{P}\p{N}\p{S}\p{M}]/.
This will though match pretty much nothing, as it allows pretty much all characters to be used - ^ at the start of a regex character class (something between [ and ]) means "everything that is not what is in this class will be matched".
On top of that, your regex will only match input that has a length of exactly one - if you want to match everything, you should begin adding a + after your closing ] to keep matching characters until the pattern fails.
So, for that sake, what exactly are you trying to achieve? Maybe we can suggest you some more regex improvements if we know what you're trying to do.
I'm still kinda new to using Regular Expressions, so here's my plight. I have some rules for acceptable usernames and I'm trying to make an expression for them.
Here they are:
1-15 Characters
a-z, A-Z, 0-9, and spaces are acceptable
Must begin with a-z or A-Z
Cannot end in a space
Cannot contain two spaces in a row
This is as far as I've gotten with it.
/^[a-zA-Z]{1}([a-zA-Z0-9]|\s(?!\s)){0,14}[^\s]$/
It works, for the most part, but doesn't match a single character such as "a".
Can anyone help me out here? I'm using PCRE in PHP if that makes any difference.
Try this:
/^(?=.{1,15}$)[a-zA-Z][a-zA-Z0-9]*(?: [a-zA-Z0-9]+)*$/
The look-ahead assertion (?=.{1,15}$) checks the length and the rest checks the structure:
[a-zA-Z] ensures that the first character is an alphabetic character;
[a-zA-Z0-9]* allows any number of following alphanumeric characters;
(?: [a-zA-Z0-9]+)* allows any number of sequences of a single space (not \s that allows any whitespace character) that must be followed by at least one alphanumeric character (see PCRE subpatterns for the syntax of (?:…)).
You could also remove the look-ahead assertion and check the length with strlen.
make everything after your first character optional
^[a-zA-Z]?([a-zA-Z0-9]|\s(?!\s)){0,14}[^\s]$
The main problem of your regexp is that it needs at least two characters two have a match :
one for the [a-zA-Z]{1} part
one for the [^\s] part
Beside this problem, I see some parts of your regexp that could be improved :
The [^\s] class will match any character, except spaces : a dot or semi-colon will be accepted, try to use the [a-zA-Z0-9] class here to ensure the character is a correct one.
You can delete the {1} part at the beginning, as the regexp will match exactly one character by default
How can I remove control characters like STX from a PHP string? I played around with
preg_replace("/[^a-zA-Z0-9 .\-_;!:?äÄöÖüÜß<>='\"]/","",$pString)
but found that it removed way to much. Is there a way to remove only
control chars?
If you mean by control characters the first 32 ascii characters and \x7F (that includes the carriage return, etc!), then this will work:
preg_replace('/[\x00-\x1F\x7F]/', '', $input);
(Note the single quotes: with double quotes the use of \x00 causes a parse error, somehow.)
The line feed and carriage return (often written \r and \n) may be saved from removal like so:
preg_replace('/[\x00-\x09\x0B\x0C\x0E-\x1F\x7F]/', '', $input);
I must say that I think Bobby's answer is better, in the sense that [:cntrl:] better conveys what the code does than [\x00-\x1F\x7F].
WARNING: ereg_replace is deprecated in PHP >= 5.3.0 and removed in PHP >= 7.0.0!, please use preg_replace instead of ereg_replace:
preg_replace('/[[:cntrl:]]/', '', $input);
For Unicode input, this will remove all control characters, unassigned, private use, formatting and surrogate code points (that are not also space characters, such as tab, new line) from your input text. I use this to remove all non-printable characters from my input.
<?php
$clean = preg_replace('/[^\PC\s]/u', '', $input);
for more info on \p{C} see http://www.regular-expressions.info/unicode.html#category
PHP does support POSIX-Classes so you can use [:cntrl:] instead of some fancy character-magic-stuff:
ereg_replace("[:cntrl:]", "", $pString);
Edit:
A extra pair of square brackets might be needed in 5.3.
ereg_replace("[[:cntrl:]]", "", $pString);
TLDR Answer
Use this Regex...
/[^\PCc^\PCn^\PCs]/u
Like this...
$text = preg_replace('/[^\PCc^\PCn^\PCs]/u', '', $text);
TLDR Explanation
^\PCc : Do not match control characters.
^\PCn : Do not match unassigned characters.
^\PCs : Do not match UTF-8-invalid characters.
Working Demo
Simple demo to demonstrate: IDEOne Demo
$text = "\u{0019}hello";
print($text . "\n\n");
$text = preg_replace('/[^\PCc^\PCn^\PCs]/u', '', $text);
print($text);
Output:
(-Broken-Character)hello
hello
Alternatives
^\PC : Match only visible characters. Do not match any invisible characters.
^\PCc : Match only non-control characters. Do not match any control characters.
^\PCc^\PCn : Match only non-control characters that have been assigned. Do not match any control or unassigned characters.
^\PCc^\PCn^\PCs : Match only non-control characters that have been assigned and are UTF-8 valid. Do not match any control, unassigned, or UTF-8-invalid characters.
^\PCc^\PCn^\PCs^\PCf : Match only non-control, non-formatting characters that have been assigned and are UTF-8 valid. Do not match any control, unassigned, formatting, or UTF-8-invalid characters.
Source and Explanation
Take a look at the Unicode Character Properties available that can be used to test within a regex. You should be able to use these regexes in Microsoft .NET, JavaScript, Python, Java, PHP, Ruby, Perl, Golang, and even Adobe. Knowing Unicode character classes is very transferable knowledge, so I recommend using it!
This regex will match anything visible, given in both its short-hand and long-hand form...
\PL\PM\PN\PP\PS\PZ
\PLetter\PMark\PNumber\PPunctuation\PSymbol\PSeparator
Normally, \p indicates that it's something we want to match and we use \P (capitalized) to indicate something that does not match. But PHP doesn't have this functionality, so we need to use ^ in the regex to do a manual negation.
A simpler regex then would be ^\PC, but this might be too restrictive in deleting invisible formatting. You may want to look closely and see what's best, but one of the alternatives should fit your needs.
All Matchable Unicode Character Sets
If you want to know any other character sets available, check out regular-expressions.info...
\PL or \PLetter: any kind of letter from any language.
\PLl or \PLowercase_Letter: a lowercase letter that has an uppercase variant.
\PLu or \PUppercase_Letter: an uppercase letter that has a lowercase variant.
\PLt or \PTitlecase_Letter: a letter that appears at the start of a word when only the first letter of the word is capitalized.
\PL& or \PCased_Letter: a letter that exists in lowercase and uppercase variants (combination of Ll, Lu and Lt).
\PLm or \PModifier_Letter: a special character that is used like a letter.
\PLo or \POther_Letter: a letter or ideograph that does not have lowercase and uppercase
\PM or \PMark: a character intended to be combined with another character (e.g. accents, umlauts, enclosing boxes, etc.).
\PMn or \PNon_Spacing_Mark: a character intended to be combined with another
character without taking up extra space (e.g. accents, umlauts, etc.).
\PMc or \PSpacing_Combining_Mark: a character intended to be combined with another character that takes up extra space (vowel signs in many Eastern languages).
\PMe or \PEnclosing_Mark: a character that encloses the character it is combined with (circle, square, keycap, etc.).
\PZ or \PSeparator: any kind of whitespace or invisible separator.
\PZs or \PSpace_Separator: a whitespace character that is invisible, but does take up space.
\PZl or \PLine_Separator: line separator character U+2028.
\PZp or \PParagraph_Separator: paragraph separator character U+2029.
\PS or \PSymbol: math symbols, currency signs, dingbats, box-drawing characters, etc.
\PSm or \PMath_Symbol: any mathematical symbol.
\PSc or \PCurrency_Symbol: any currency sign.
\PSk or \PModifier_Symbol: a combining character (mark) as a full character on its own.
\PSo or \POther_Symbol: various symbols that are not math symbols, currency signs, or combining characters.
\PN or \PNumber: any kind of numeric character in any script.
\PNd or \PDecimal_Digit_Number: a digit zero through nine in any script except ideographic scripts.
\PNl or \PLetter_Number: a number that looks like a letter, such as a Roman numeral.
\PNo or \POther_Number: a superscript or subscript digit, or a number that is not a digit 0–9 (excluding numbers from ideographic scripts).
\PP or \PPunctuation: any kind of punctuation character.
\PPd or \PDash_Punctuation: any kind of hyphen or dash.
\PPs or \POpen_Punctuation: any kind of opening bracket.
\PPe or \PClose_Punctuation: any kind of closing bracket.
\PPi or \PInitial_Punctuation: any kind of opening quote.
\PPf or \PFinal_Punctuation: any kind of closing quote.
\PPc or \PConnector_Punctuation: a punctuation character such as an underscore that connects words.
\PPo or \POther_Punctuation: any kind of punctuation character that is not a dash, bracket, quote or connector.
\PC or \POther: invisible control characters and unused code points.
\PCc or \PControl: an ASCII or Latin-1 control character: 0x00–0x1F and 0x7F–0x9F.
\PCf or \PFormat: invisible formatting indicator.
\PCo or \PPrivate_Use: any code point reserved for private use.
\PCs or \PSurrogate: one half of a surrogate pair in UTF-16 encoding.
\PCn or \PUnassigned: any code point to which no character has been assigned.
To keep the control characters but make them compatible for JSON, I had to to
$str = preg_replace(
array(
'/\x00/', '/\x01/', '/\x02/', '/\x03/', '/\x04/',
'/\x05/', '/\x06/', '/\x07/', '/\x08/', '/\x09/', '/\x0A/',
'/\x0B/','/\x0C/','/\x0D/', '/\x0E/', '/\x0F/', '/\x10/', '/\x11/',
'/\x12/','/\x13/','/\x14/','/\x15/', '/\x16/', '/\x17/', '/\x18/',
'/\x19/','/\x1A/','/\x1B/','/\x1C/','/\x1D/', '/\x1E/', '/\x1F/'
),
array(
"\u0000", "\u0001", "\u0002", "\u0003", "\u0004",
"\u0005", "\u0006", "\u0007", "\u0008", "\u0009", "\u000A",
"\u000B", "\u000C", "\u000D", "\u000E", "\u000F", "\u0010", "\u0011",
"\u0012", "\u0013", "\u0014", "\u0015", "\u0016", "\u0017", "\u0018",
"\u0019", "\u001A", "\u001B", "\u001C", "\u001D", "\u001E", "\u001F"
),
$str
);
(The JSON rules state: “All Unicode characters may be placed within the quotation marks except for the characters that must be escaped: quotation mark, reverse solidus, and the control characters (U+0000 through U+001F).”)
regex free method
If you are only zapping the control characters I'm familiar with (those under 32 and 127), try this out:
for($control = 0; $control < 32; $control++) {
$pString = str_replace(chr($control), "", $pString;
}
$pString = str_replace(chr(127), "", $pString;
The loop gets rid of all but DEL, which we just add to the end.
I'm thinking this will be a lot less stressful on you and the script then dealing with regex and the regex library.
Updated regex free method
Just for kicks, I came up with another way to do it. This one does it using an array of control characters:
$ctrls = range(chr(0), chr(31));
$ctrls[] = chr(127);
$clean_string = str_replace($ctrls, "", $string);