Heredoc and nowdoc syntax in PHP - Step-by-Step Execution

Concept Flow - Heredoc and nowdoc syntax

Start

↓

Define Heredoc

↓

Assign multiline string

↓

Use variable inside string?

↓

Parse variables

↓

End Heredoc

↓

Use string

↓

End

Shows how heredoc and nowdoc define multiline strings, with heredoc parsing variables and nowdoc treating content literally.

Execution Sample

PHP

<?php
$name = "Anna";
$heredoc = <<<EOD
Hello, $name!
EOD;
$nowdoc = <<<'EOD'
Hello, $name!
EOD;
echo $heredoc;
echo $nowdoc;
?>

Defines a variable, then creates a heredoc string that parses the variable, and a nowdoc string that treats it literally.

Execution Table

Step	Action	Code Line	Variable Values	Output/Result
1	Assign $name	$name = "Anna";	$name = "Anna"	No output
2	Start heredoc assignment	$heredoc = <<<EOD	$heredoc = (not set yet)	No output
3	Assign heredoc content with variable parsed	Hello, $name!	$heredoc = "Hello, Anna!\n"	No output
4	End heredoc	EOD;	$heredoc = "Hello, Anna!\n"	No output
5	Start nowdoc assignment	$nowdoc = <<<'EOD'	$nowdoc = (not set yet)	No output
6	Assign nowdoc content literally	Hello, $name!	$nowdoc = "Hello, $name!\n"	No output
7	End nowdoc	EOD;	$nowdoc = "Hello, $name!\n"	No output
8	Print heredoc	echo $heredoc;	$heredoc = "Hello, Anna!\n"	Hello, Anna!
9	Print nowdoc	echo $nowdoc;	$nowdoc = "Hello, $name!\n"	Hello, $name!
10	End script	?>	All variables set	Script ends

💡 Script ends after printing both heredoc and nowdoc strings

Variable Tracker

Variable	Start	After Step 1	After Step 4	After Step 7	Final
$name	undefined	"Anna"	"Anna"	"Anna"	"Anna"
$heredoc	undefined	undefined	"Hello, Anna!\n"	"Hello, Anna!\n"	"Hello, Anna!\n"
$nowdoc	undefined	undefined	undefined	"Hello, $name!\n"	"Hello, $name!\n"

Key Moments - 2 Insights

Why does $name get replaced inside heredoc but not inside nowdoc?

In the execution_table rows 3 and 6, heredoc parses variables like $name and replaces them with their values, while nowdoc treats everything literally, so $name stays as text.

Why do heredoc and nowdoc both end with the same marker but behave differently?

As shown in rows 4 and 7, the marker EOD ends both strings, but heredoc uses <<<EOD (without quotes) which enables variable parsing, while nowdoc uses <<<'EOD' (with single quotes) which disables parsing.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what is the value of $heredoc?

A "Hello, $name!\n"

B "Hello, Anna!\n"

C "Hello, Anna!"

D "Hello, $name!"

💡 Hint

Check the 'Variable Values' column at step 3 in execution_table

At which step does $nowdoc get assigned its value?

A Step 7

B Step 6

C Step 4

D Step 2

💡 Hint

Look at when $nowdoc is set in the 'Variable Values' column in execution_table

If we change nowdoc marker to <<<EOD (without quotes), what happens to $nowdoc content?

A Syntax error occurs

B Content remains literal with variables unparsed

C Variables inside $nowdoc will be parsed

D Nowdoc will be empty

💡 Hint

Refer to key_moments about difference between heredoc and nowdoc markers

Concept Snapshot

Heredoc syntax: <<<LABEL starts multiline string, variables inside are parsed.
Nowdoc syntax: <<<'LABEL' starts multiline string, content is literal, no parsing.
Both end with LABEL on a line alone.
Use heredoc for strings with variables, nowdoc for raw text.
Markers must be alone on their line with no spaces.

Full Transcript

This visual execution shows how PHP heredoc and nowdoc syntax work. We start by assigning a variable $name with value "Anna". Then we create a heredoc string using <<<EOD which allows variable parsing, so $name inside the string becomes "Anna". Next, we create a nowdoc string using <<<'EOD' which treats the content literally, so $name stays as text. Both strings end with the marker EOD on a line alone. Finally, printing the heredoc outputs "Hello, Anna!" while printing the nowdoc outputs "Hello, $name!" exactly as typed. This helps beginners see how heredoc parses variables and nowdoc does not, even though both use similar syntax markers.