PHP Add Array Items
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Appending with the [] Syntax
$arr[] = $value is the simplest and most common way to append a single new item to an indexed array -- PHP automatically figures out the next available numeric index and assigns the value there, without you needing to track the current length yourself.
Note: Use $arr[] = $value as your default way to add one item at a time, especially inside a loop building up results.
Warning: The [] append syntax always adds to the highest existing numeric key + 1 -- if an array has gaps or unusual keys, the next appended index may not be what you expect.
Example: Appending with the [] Syntax
<?php
$fruits = ["Apple", "Banana"];
$fruits[] = "Cherry";
print_r($fruits);
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Adding Multiple Items with array_push()
array_push($arr, $value1, $value2, ...) appends one or more values to the end of an array in a single call, which is useful when you already have several new values ready to add at once instead of appending them one at a time.
Note: For a single item, $arr[] = $value is simpler and marginally faster than calling array_push() with one argument.
Warning: array_push() modifies the array it is given directly (by reference) -- it does not return a new array, so there is no need to reassign the result.
Example: Adding Multiple Items with array_push()
<?php
$fruits = ["Apple"];
array_push($fruits, "Banana", "Cherry");
print_r($fruits);
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Adding Items at the Beginning with array_unshift()
array_unshift($arr, $value1, $value2, ...) inserts one or more values at the very start of an array, shifting every existing item to a higher index -- the opposite end from array_push(), useful for adding a "most recent" item to the front of a list.
Note: Be aware that array_unshift() re-indexes every existing numeric key afterward, so any code relying on specific original index numbers will need to account for the shift.
Warning: array_unshift() is noticeably slower than array_push() on large arrays, since every existing element's index has to shift.
Example: Adding Items at the Beginning with array_unshift()
<?php
$queue = ["Bob", "Carol"];
array_unshift($queue, "Alice");
print_r($queue);
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Adding a New Associative Key
Adding a new key to an associative array is as simple as assigning a value to a key that does not exist yet: $person["email"] = "[email protected]" creates the "email" key if it was not already present, exactly like a normal assignment.
Note: Check whether a key already exists with isset() first if you specifically need to avoid accidentally overwriting an existing value.
Warning: Because adding and updating a key use identical syntax, PHP will silently overwrite an existing key rather than warn you that you meant to add a brand-new one.
Example: Adding a New Associative Key
<?php
$person = ["name" => "Alice"];
$person["email"] = "[email protected]";
print_r($person);
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Merging Two Arrays Together
array_merge($arr1, $arr2) combines two arrays into one new array, effectively adding every item from the second array onto the first -- for indexed arrays it re-numbers keys sequentially, while for associative arrays with matching keys, the later array's values win.
Note: Use array_merge() specifically when adding many items from an existing second array at once, rather than looping and appending each one manually.
Warning: array_merge() on two associative arrays with the same key does not combine the values -- the second array's value for that key simply overwrites the first's.
Example: Merging Two Arrays Together
<?php
$arr1 = ["a", "b"];
$arr2 = ["c", "d"];
print_r(array_merge($arr1, $arr2));
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- Using $arr[0] = $value to "add" an item, which actually overwrites index 0 if it already exists, instead of appending a genuinely new item.
- Forgetting that array_push() and array_unshift() re-index all numeric keys afterward, which can shift indexes you were relying on elsewhere.
- Adding items inside a loop with array_push($arr, $item) instead of the simpler $arr[] = $item, which is both shorter and slightly faster for single-item appends.
- $arr[] = $value appends a new item to the end of an indexed array, automatically assigning it the next numeric index.
- array_push($arr, ...$values) appends one or more values to the end; array_unshift($arr, ...$values) inserts them at the start.
- Adding a new associative key is as simple as $arr["newKey"] = $value -- if the key does not already exist, it is created.
All array-appending functions and syntax discussed here have been part of PHP since its earliest array support.
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