PHPWales 2020 - June 3rd to June 4th

preg_grep

(PHP 4, PHP 5, PHP 7)

preg_grepReturn array entries that match the pattern

Description

preg_grep ( string $pattern , array $input [, int $flags = 0 ] ) : array

Returns the array consisting of the elements of the input array that match the given pattern.

Parameters

pattern

The pattern to search for, as a string.

input

The input array.

flags

If set to PREG_GREP_INVERT, this function returns the elements of the input array that do not match the given pattern.

Return Values

Returns an array indexed using the keys from the input array.

Examples

Example #1 preg_grep() example

<?php
// return all array elements
// containing floating point numbers
$fl_array preg_grep("/^(\d+)?\.\d+$/"$array);
?>

See Also

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User Contributed Notes 4 notes

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58
Daniel Klein
6 years ago
A shorter way to run a match on the array's keys rather than the values:

<?php
function preg_grep_keys($pattern, $input, $flags = 0) {
    return
array_intersect_key($input, array_flip(preg_grep($pattern, array_keys($input), $flags)));
}
?>
up
30
keithbluhm at gmail dot com
9 years ago
Run a match on the array's keys rather than the values:

<?php

function preg_grep_keys( $pattern, $input, $flags = 0 )
{
   
$keys = preg_grep( $pattern, array_keys( $input ), $flags );
   
$vals = array();
    foreach (
$keys as $key )
    {
       
$vals[$key] = $input[$key];
    }
    return
$vals;
}

?>
up
2
amolocaleb at gmail dot com
1 year ago
This may be obvious to most experienced developers,but just in case its not,when using preg_grep to check for whitelisted items ,one must be very careful to explicitly define the regex boundaries or it will fail
<?php
$whitelist
= ["home","dashboard","profile","group"];
$possibleUserInputs = ["homd","hom","ashboard","settings","group"];
foreach(
$possibleUserInputs as  $input)
{
     if(
preg_grep("/$input/i",$whitelist)
    {
         echo
$input." whitelisted";
    }else{
         echo
$input." flawed";
    }

}
?>
This results in:

homd flawed
hom whitelisted
ashboard whitelisted
settings flawed
group whitelisted

I think this is because if boundaries are not explicitly defined,preg_grep looks for any instance of  the substring in the whole array and returns true if found.This is not what we want,so boundaries must be defined.

<?php
foreach($possibleUserInputs as  $input)
{
     if(
preg_grep("/^$input$/i",$whitelist)
    {
         echo
$input." whitelisted";
    }else{
         echo
$input." flawed";
    }

}
?>
this results in:
homd flawed
hom flawed
ashboard flawed
settings flawed
group whitelisted
in_array() will also give the latter results but will require few tweaks if say,the search is to be case insensitive,which is always the case 70% of the time
up
-18
Timo Klemm
2 years ago
An even shorter way to run a match on the array's keys rather than the values:

<?php
function preg_grep_keys($pattern, $input, $flags = 0) {
    return
array_flip( preg_grep($pattern, array_flip($input), $flags ) );
}
?>
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