String replace functions in PHP - Step-by-Step Execution

Concept Flow - String replace functions

Start with original string

↓

Call string replace function

↓

Search for target substring

↓

Replace substring

↓

Return modified string

↓

End

The string replace function searches the original string for a target substring. If found, it replaces it with a new substring and returns the modified string. If not found, it returns the original string unchanged.

Execution Sample

PHP

<?php
$original = "Hello world!";
$modified = str_replace("world", "PHP", $original);
echo $modified;
?>

This code replaces the word 'world' with 'PHP' in the original string and prints the result.

Execution Table

Step	Action	Input String	Search Substring	Replace Substring	Result String	Output
1	Start with original string	Hello world!			Hello world!
2	Call str_replace function	Hello world!	world	PHP
3	Search for 'world' in string	Hello world!	world	PHP		Found at position 6
4	Replace 'world' with 'PHP'	Hello world!	world	PHP	Hello PHP!
5	Return modified string	Hello world!	world	PHP	Hello PHP!	Hello PHP!
6	Print output	Hello world!	world	PHP	Hello PHP!	Hello PHP!

💡 Replacement done and modified string returned and printed.

Variable Tracker

Variable	Start	After str_replace	Final
$original	"Hello world!"	"Hello world!"	"Hello world!"
$modified	undefined	"Hello PHP!"	"Hello PHP!"

Key Moments - 2 Insights

Why does the original string $original not change after str_replace?

Because str_replace returns a new string with replacements and does not modify the original string variable. See execution_table step 5 where $modified gets the new string but $original stays the same.

What happens if the search substring is not found in the original string?

The function returns the original string unchanged. This is shown in execution_table step 3 where if 'world' was not found, the original string would be returned without changes.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of $modified after step 4?

A "Hello PHP!"

B "Hello world!"

C "PHP world!"

D "Hello!"

💡 Hint

Check the 'Result String' column at step 4 in execution_table.

At which step does the function confirm the substring 'world' is found?

A Step 2

B Step 3

C Step 5

D Step 6

💡 Hint

Look at the 'Output' column in execution_table for the step that mentions 'Found at position'.

If the search substring was 'planet' instead of 'world', what would $modified be after str_replace?

A "Hello PHP!"

B "Hello planet!"

C "Hello world!"

D "PHP planet!"

💡 Hint

Refer to key_moments about what happens if the substring is not found.

Concept Snapshot

str_replace(search, replace, string) replaces all occurrences of search with replace in string.
Returns a new string; original string stays unchanged.
If search not found, returns original string.
Useful for simple text substitutions.

Full Transcript

This example shows how PHP's str_replace function works. We start with the original string 'Hello world!'. The function searches for the substring 'world'. It finds it at position 6. Then it replaces 'world' with 'PHP', creating 'Hello PHP!'. The function returns this new string, which we store in $modified. The original string $original remains unchanged. Finally, we print the modified string. If the search substring was not found, the function would return the original string unchanged.