I have been looking around and googling about regex and I came up with this to make sure some variable has letters in it (and nothing else).
/^[a-zA-Z]*$/
In my mind ^ denotes the start of the string, the token [a-zA-Z] should in my mind make sure only letters are allowed. The star should match everything in the token, and the $-sign denotes the end of the string I'm trying to match.
But it doesn't work, when I try it on regexr it doesn't work sadly. What's the correct way to do it then? I would also like to allow hyphen and spaces, but figured just starting with letters are good enough to start with and expand.
Short answer : this is what you are looking for.
/^[a-zA-Z]+$/
The star * quantifier means "zero or more", meaning your regexp will match everytime even with an empty string as subject. You need the + quantifier instead (meaning "one or more") to achieve what you need.
If you also want to match at least one character which could also be a whitespace or a hyphen you could add those to your character class ^[A-Za-z -]+$ using the plus + sign for the repetition.
If you want to use preg_match to match at least one character which can contain an upper or lowercase character, you could shorten your pattern to ^[a-z]+$ and use the i modifier to make the regex case insensitive. To also match a hyphen and a whitespace, this could look like ^[a-z -]+$
For example:
$strings = [
"TeSt",
"Te s-t",
"",
"Te4St"
];
foreach ($strings as $string) {
if(preg_match('#^[a-z -]+$#i', $string, $matches)){
echo $matches[0] . PHP_EOL;
}
}
That would result in:
TeSt
Te s-t
Output php
header.php file
<?php
echo 'this is example '.$adv['name'].' , this is another.....';
main.php file
<?php
if(preg_match('/$adv[(.*?)]/',file_get_contents('header.php'),$itext)){
echo $itext[1].'';
}
show empty
this regular expression will work
/\$adv\[(.*?)\]/
You need to escape symbols $,[,] using \ before them
since they have special meaning in regular expressions
Here is a more efficient solution:
Pattern (Demo):
/\$adv\[\K[^]]*?(?=\])/
PHP Implementation:
if(preg_match('/\$adv\[\K[^]]*?(?=\])/','this is example $adv[name]',$itext)){
echo $itext[0];
}
Output for $itext:
name
Notice that by using \K to replace the capture group, the targeted string is returned in the "full string" match which effectively reduces the output array by 50%.
You can see the demo link for explanation on individual pieces of the pattern, but basically it matches $adv[ then resets the matching point, matches all characters between the square brackets, then does a positive lookahead for a closing square bracket which will not be included in the returned match.
Regardless of if you want to match different variable names you could use: /\$[^[]*?\[\K[^]]*?(?=\])/. This will accommodate adv or any other substring that follows the dollar sign. By using Negated Character Classes like [^]] instead of . to match unlimited characters, the regex pattern performs more efficiently.
If adv is not a determining component of your input strings, I would use /\$[^[]*?\[\K[^]]*?(?=\])/ because it will be the most efficient.
I'm trying to validate some input, but I'm getting reverse results (or maybe I have completely missed the use of the preg_match function?)
This is my code:
$check_firstname = "##";
if(preg_match('/[^A-Za-z0-9_]/', $check_firstname)) echo "valid"; else echo "invalid";
I would have thought that this regex in preg_match would not only allow alphanumeric characters, but this input gives an output of valid! If the input (in this case, check_firstname) is NOT alphanumeric, why is preg_match finding a match? I've already checked the documentation but I don't understand what's happening.
My real requirement is to allow the dash character (-) along with alphanumeric characters in the user input, but I don't see how to get anywhere when my basic test seems not to be working.
Edit
Thank you for your responses! I get the problem with the caret now. However I forgot mention that apart from dashes, I need to allow spaces as well.
You're using the ^ symbol which means "not" when it's inside of brackets. Here's a good site on syntax for Regex. In single line mode, the \s allows for tabs and spaces. Note: the hyphen needs to go last so it doesn't try and treat it like a range.
if(preg_match('/^[A-Z0-9\s-]+$/i', $check_firstname)){
echo "valid"; } else {echo "invalid";}
You simply put the caret (^) in the wrong position :)
[^...] matches any character not found between the square brackets.
^ alone means the beginning of the string.
[^A-Za-z0-9_] means that the regex will check for the first character in the string and if that character is not an alphanumeric, or underscore, it will pass.
To allow only alphanumeric characters and a dash, you will use:
^[A-Za-z0-9-]+$
The + (one or more times) and $ (end of string) operators will ensure that the whole string is checked.
Note that this regex doesn't allow underscores (_). If you need to allow them, you can use the regex in Casimir's answer.
To allow spaces as well:
^[A-Za-z0-9\s-]+$
Try this:
if(preg_match('/^[A-Za-z0-9_]+$/', $check_firstname)===1){ echo 'Valid'; } else { echo 'Invalid'; }
Just incorrect place to put the ^ character, and also added the $ symbol to indicate the end of the match.
You should also be using a type/value comparison as this function can return 3 different values:
(int)1 = Match found
(int)0 = Match not found
(bool)false = Error
You could use this:
if(preg_match('/^[\w- ]+$/', $check_firstname)) echo "valid"; else echo "invalid";
Why not stick with your regex and change the interpretation?
if(preg_match('/[^A-Za-z0-9_]/', $check_firstname)) echo "invalid"; else echo "valid";
If the regex matches, you know that $check_firstname contains at least one char that is not a letter, a number or underscore --> that makes it invalid
qed
I am trying to search for some pattern in PHP with the help of preg_match. Search pattern is like this (but this is wrong):
/[\d\s*-\s*\d\s*(usd|eur)]{1}/i
\d starts with integer,
\s* there can be any number of whitespaces,
- there must be exactly one minus sign
\s* there can be any number of whitespaces,
\d then must be integer
\s* there can be any number of whitespaces,
(usd|eur) any of the following words must be present but one
[\d\s*-\s*\d\s*(usd|eur)]{1} - in string there should be exactly one occurence
the above pattern does not work, what I am doing wrong? For testing:
<?php
$pattern = '/[\d\s*-\s*\d\s*(usd|eur)]{1}/i';
$query = '100-120 100-120';
echo $pattern.'<br/>';
echo $query.'<br/>';
if(preg_match($pattern, $query))
echo 'OK';
else
echo 'not OK!';
?>
Note:
I am trying to pull out data like this:
The price of item is 100 - 120 usd in our market
[...] is a character class. It means "match any one of these characters". [abc] will match a,b, or c. It doesn't match the string "abc".
In addition:
{1} means "match the preceding expression one time". However, matching once is the default. There is no need to explicitly tell it to match one time.
\d matches a single numeric digit. Based on your example, you want \d+ - match a number made up of at least one digit.
Here is what your pattern should look like:
/\d+\s*-\s*\d+\s*(usd|eur)/i
Regular expressions are a powerful tool for examining and modifying text. Regular expressions themselves, with a general pattern notation almost like a mini programming language, allow you to describe and parse text. They enable you to search for patterns within a string, extracting matches flexibly and precisely. However, you should note that because regular expressions are more powerful, they are also slower than the more basic string functions. You should only use regular expressions if you have a particular need.
This tutorial gives a brief overview of basic regular expression syntax and then considers the functions that PHP provides for working with regular expressions.
The Basics
Matching Patterns
Replacing Patterns
Array Processing
PHP supports two different types of regular expressions: POSIX-extended and Perl-Compatible Regular Expressions (PCRE). The PCRE functions are more powerful than the POSIX ones, and faster too, so we will concentrate on them.
The Basics
In a regular expression, most characters match only themselves. For instance, if you search for the regular expression "foo" in the string "John plays football," you get a match because "foo" occurs in that string. Some characters have special meanings in regular expressions. For instance, a dollar sign ($) is used to match strings that end with the given pattern. Similarly, a caret (^) character at the beginning of a regular expression indicates that it must match the beginning of the string. The characters that match themselves are called literals. The characters that have special meanings are called metacharacters.
The dot (.) metacharacter matches any single character except newline (). So, the pattern h.t matches hat, hothit, hut, h7t, etc. The vertical pipe (|) metacharacter is used for alternatives in a regular expression. It behaves much like a logical OR operator and you should use it if you want to construct a pattern that matches more than one set of characters. For instance, the pattern Utah|Idaho|Nevada matches strings that contain "Utah" or "Idaho" or "Nevada". Parentheses give us a way to group sequences. For example, (Nant|b)ucket matches "Nantucket" or "bucket". Using parentheses to group together characters for alternation is called grouping.
If you want to match a literal metacharacter in a pattern, you have to escape it with a backslash.
To specify a set of acceptable characters in your pattern, you can either build a character class yourself or use a predefined one. A character class lets you represent a bunch of characters as a single item in a regular expression. You can build your own character class by enclosing the acceptable characters in square brackets. A character class matches any one of the characters in the class. For example a character class [abc] matches a, b or c. To define a range of characters, just put the first and last characters in, separated by hyphen. For example, to match all alphanumeric characters: [a-zA-Z0-9]. You can also create a negated character class, which matches any character that is not in the class. To create a negated character class, begin the character class with ^: [^0-9].
The metacharacters +, *, ?, and {} affect the number of times a pattern should be matched. + means "Match one or more of the preceding expression", * means "Match zero or more of the preceding expression", and ? means "Match zero or one of the preceding expression". Curly braces {} can be used differently. With a single integer, {n} means "match exactly n occurrences of the preceding expression", with one integer and a comma, {n,} means "match n or more occurrences of the preceding expression", and with two comma-separated integers {n,m} means "match the previous character if it occurs at least n times, but no more than m times".
Now, have a look at the examples:
Regular Expression Will match...
foo The string "foo"
^foo "foo" at the start of a string
foo$ "foo" at the end of a string
^foo$ "foo" when it is alone on a string
[abc] a, b, or c
[a-z] Any lowercase letter
[^A-Z] Any character that is not a uppercase letter
(gif|jpg) Matches either "gif" or "jpeg"
[a-z]+ One or more lowercase letters
[0-9\.\-] Аny number, dot, or minus sign
^[a-zA-Z0-9_]{1,}$ Any word of at least one letter, number or _
([wx])([yz]) wy, wz, xy, or xz
[^A-Za-z0-9] Any symbol (not a number or a letter)
([A-Z]{3}|[0-9]{4}) Matches three letters or four numbers
Perl-Compatible Regular Expressions emulate the Perl syntax for patterns, which means that each pattern must be enclosed in a pair of delimiters. Usually, the slash (/) character is used. For instance, /pattern/.
The PCRE functions can be divided in several classes: matching, replacing, splitting and filtering.
Matching Patterns
The preg_match() function performs Perl-style pattern matching on a string. preg_match() takes two basic and three optional parameters. These parameters are, in order, a regular expression string, a source string, an array variable which stores matches, a flag argument and an offset parameter that can be used to specify the alternate place from which to start the search:
preg_match ( pattern, subject [, matches [, flags [, offset]]])
The preg_match() function returns 1 if a match is found and 0 otherwise. Let's search the string "Hello World!" for the letters "ll":
<?php
if (preg_match("/ell/", "Hello World!", $matches)) {
echo "Match was found <br />";
echo $matches[0];
}
?>
The letters "ll" exist in "Hello", so preg_match() returns 1 and the first element of the $matches variable is filled with the string that matched the pattern. The regular expression in the next example is looking for the letters "ell", but looking for them with following characters:
<?php
if (preg_match("/ll.*/", "The History of Halloween", $matches)) {
echo "Match was found <br />";
echo $matches[0];
}
?>
Now let's consider more complicated example. The most popular use of regular expressions is validation. The example below checks if the password is "strong", i.e. the password must be at least 8 characters and must contain at least one lower case letter, one upper case letter and one digit:
<?php
$password = "Fyfjk34sdfjfsjq7";
if (preg_match("/^.*(?=.{8,})(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$/", $password)) {
echo "Your passwords is strong.";
} else {
echo "Your password is weak.";
}
?>
The ^ and $ are looking for something at the start and the end of the string. The ".*" combination is used at both the start and the end. As mentioned above, the .(dot) metacharacter means any alphanumeric character, and * metacharacter means "zero or more". Between are groupings in parentheses. The "?=" combination means "the next text must be like this". This construct doesn't capture the text. In this example, instead of specifying the order that things should appear, it's saying that it must appear but we're not worried about the order.
The first grouping is (?=.{8,}). This checks if there are at least 8 characters in the string. The next grouping (?=.[0-9]) means "any alphanumeric character can happen zero or more times, then any digit can happen". So this checks if there is at least one number in the string. But since the string isn't captured, that one digit can appear anywhere in the string. The next groupings (?=.[a-z]) and (?=.[A-Z]) are looking for the lower case and upper case letter accordingly anywhere in the string.
Finally, we will consider regular expression that validates an email address:
<?php
$email = firstname.lastname#aaa.bbb.com;
$regexp = "/^[^0-9][A-z0-9_]+([.][A-z0-9_]+)*[#][A-z0-9_]+([.][A-z0-9_]+)*[.][A-z]{2,4}$/";
if (preg_match($regexp, $email)) {
echo "Email address is valid.";
} else {
echo "Email address is <u>not</u> valid.";
}
?>
This regular expression checks for the number at the beginning and also checks for multiple periods in the user name and domain name in the email address. Let's try to investigate this regular expression yourself.
For the speed reasons, the preg_match() function matches only the first pattern it finds in a string. This means it is very quick to check whether a pattern exists in a string. An alternative function, preg_match_all(), matches a pattern against a string as many times as the pattern allows, and returns the number of times it matched.
Replacing Patterns
In the above examples, we have searched for patterns in a string, leaving the search string untouched. The preg_replace() function looks for substrings that match a pattern and then replaces them with new text. preg_replace() takes three basic parameters and an additional one. These parameters are, in order, a regular expression, the text with which to replace a found pattern, the string to modify, and the last optional argument which specifies how many matches will be replaced.
preg_replace( pattern, replacement, subject [, limit ])
The function returns the changed string if a match was found or an unchanged copy of the original string otherwise. In the following example we search for the copyright phrase and replace the year with the current.
<?php
echo preg_replace("/([Cc]opyright) 200(3|4|5|6)/", "$1 2007", "Copyright 2005");
?>
In the above example we use back references in the replacement string. Back references make it possible for you to use part of a matched pattern in the replacement string. To use this feature, you should use parentheses to wrap any elements of your regular expression that you might want to use. You can refer to the text matched by subpattern with a dollar sign ($) and the number of the subpattern. For instance, if you are using subpatterns, $0 is set to the whole match, then $1, $2, and so on are set to the individual matches for each subpattern.
In the following example we will change the date format from "yyyy-mm-dd" to "mm/dd/yyy":
<?php
echo preg_replace("/(\d+)-(\d+)-(\d+)/", "$2/$3/$1", "2007-01-25");
?>
We also can pass an array of strings as subject to make the substitution on all of them. To perform multiple substitutions on the same string or array of strings with one call to preg_replace(), we should pass arrays of patterns and replacements. Have a look at the example:
<?php
$search = array ( "/(\w{6}\s\(w{2})\s(\w+)/e",
"/(\d{4})-(\d{2})-(\d{2})\s(\d{2}:\d{2}:\d{2})/");
$replace = array ('"$1 ".strtoupper("$2")',
"$3/$2/$1 $4");
$string = "Posted by John | 2007-02-15 02:43:41";
echo preg_replace($search, $replace, $string);?>
In the above example we use the other interesting functionality - you can say to PHP that the match text should be executed as PHP code once the replacement has taken place. Since we have appended an "e" to the end of the regular expression, PHP will execute the replacement it makes. That is, it will take strtoupper(name) and replace it with the result of the strtoupper() function, which is NAME.
Array Processing
PHP's preg_split() function enables you to break a string apart basing on something more complicated than a literal sequence of characters. When it's necessary to split a string with a dynamic expression rather than a fixed one, this function comes to the rescue. The basic idea is the same as preg_match_all() except that, instead of returning matched pieces of the subject string, it returns an array of pieces that didn't match the specified pattern. The following example uses a regular expression to split the string by any number of commas or space characters:
<?php
$keywords = preg_split("/[\s,]+/", "php, regular expressions");
print_r( $keywords );
?>
Another useful PHP function is the preg_grep() function which returns those elements of an array that match a given pattern. This function traverses the input array, testing all elements against the supplied pattern. If a match is found, the matching element is returned as part of the array containing all matches. The following example searches through an array and all the names starting with letters A-J:
<?php
$names = array('Andrew','John','Peter','Nastin','Bill');
$output = preg_grep('/^[a-m]/i', $names);
print_r( $output );
?>
<?php
$string = 'user34567';
if(preg_match('/user(^[0-9]{1,8}+$)/', $string)){
echo 1;
}
?>
I want to check if the string have the word user follows by number that can be 8 symbols max.
You're very close actually:
if(preg_match('/^user[0-9]{1,8}$/', $string)){
The anchor for "must match at start of string" should be all the way in front, followed by the "user" literal; then you specify the character set [0-9] and multiplier {1,8}. Finally, you end off with the "must match at end of string" anchor.
A few comments on your original expression:
The ^ matches the start of a string, so writing it anywhere else inside this expression but the beginning will not yield the expected results
The + is a multiplier; {1,8} is one too, but only one multiplier can be used after an expression
Unless you're intending to use the numbers that you found in the expression, you don't need parentheses.
Btw, instead of [0-9] you could also use \d. It's an automatic character group that shortens the regular expression, though this particular one doesn't save all too many characters ;-)
By using ^ and $, you are only matching when the pattern is the only thing on the line. Is that what you want? If so, use the following:
preg_match( '/^user[0-9]{1,8}[^0-9]$/' , $string );
If you want to find this pattern anywhere in a line, I would try:
preg_match( '/user[0-9]{1,8}[^0-9]/' , $string );
As always, you should use a reference tool like RegexPal to do your regular expression testing in isolation.
You were close, here is your regex : /^user[0-9]{1,8}$/
try the following regex instead:
/^user([0-9]{1,8})$/
Use this regex:
/^user\d{1,8}$/