Heredoc處理變量插值和基本轉(zhuǎn)義序列如\n、\t、\\、\$，但不處理\"或\'，而Nowdoc不進(jìn)行變量插值和任何轉(zhuǎn)義處理，所有內(nèi)容包括\n和變量均按字面輸出；1. Heredoc中變量如$name會(huì)被替換，\\n被解析為換行；2. Nowdoc中$name和\n均保持原樣；3. 兩者都不需要轉(zhuǎn)義引號(hào)；4. 結(jié)束標(biāo)識(shí)符必須獨(dú)占一行且無前導(dǎo)空格，PHP 7.3 允許使用空格縮進(jìn)結(jié)束標(biāo)識(shí)符。因此Heredoc適用於需格式化的多行字符串，Nowdoc適合輸出原始內(nèi)容如SQL或JavaScript代碼。

PHP's Heredoc and Nowdoc syntaxes provide a clean way to define multi-line strings. While they look similar, their handling of escape characters and variable interpolation differs significantly. Understanding how escape characters behave in each is key to using them correctly.

Heredoc: Variables and Escape Sequences Are Processed

Heredoc behaves like a double-quoted string — it allows variable interpolation and interprets certain escape sequences , though not all in the way you might expect.

 $name = "Alice";
echo <<<EOT
Hello $name,
This is line one.\nThis is line two.
EOT;

Output:

 Hello Alice,
This is line one.
This is line two.

Here, two things happen:

• $name is interpolated to "Alice"
• \n is interpreted as a newline character

But note: only basic escape sequences like \n , \r , \t , \\ , and \$ are processed in Heredoc. Sequences like \" or \' are not special and will appear literally.

 echo <<<EOT
He said: \"Hello\"
EOT;

Output:

 He said: \"Hello\"

So even though Heredoc processes some escapes, quotes don't need to be escaped — you can freely use " or ' without backslashes.

? Bottom line: Heredoc handles \n , \t , \\ , \$ , etc., and interpolates variables. Other escape sequences (like \" ) are ignored and output as-is.

Nowdoc: No Escaping, No Interpolation

Nowdoc is like a single-quoted string — no variable interpolation , and almost no escape processing at all. It's designed for raw, literal strings.

You define it using single quotes around the identifier:

 echo <<<&#39;EOT&#39;
Hello $name,
This is line one.\nThis is line two.
EOT;

Output:

 Hello $name,
This is line one.\nThis is line two.

Everything is taken literally:

• $name is not replaced
• \n is not converted to a newline
• Even \\ remains as two characters: backslash backslash

The only "escape" behavior in Nowdoc is that you can include the closing identifier ( EOT in this case) inside the content — as long as it's not on its own line, at the start of the line, with no extra whitespace.

So this is safe:

 echo <<<&#39;EOT&#39;
This is not the end: EOT here
EOT;

But this will end the string prematurely:

 echo <<<&#39;EOT&#39;
This ends here
EOT
More text here
EOT;

Only the first EOT closes the string — the rest causes a parse error.

Key Differences Summary

Practical Tips

• Use Heredoc when you need readable multi-line strings with variables or newlines.
• Use Nowdoc for raw output — like embedding JavaScript, SQL, or configuration snippets without interpolation.
• Don't escape quotes in either syntax — just use them freely.
• Be careful with the closing identifier — it must be at the start of a line with no extra spaces or tabs.
• Indentation: PHP 7.3 allows closing identifier to be indented with spaces only if the heredoc is defined with a closing tag on a new line.

Example with indentation (PHP 7.3 ):

 $message = <<<EOT
    Line one
    Line two
    EOT; // Allowed if EOT is on its own line

Basically, Heredoc gives you flexibility; Nowdoc gives you predictability. Know how escape characters behave in each, and you'll avoid subtle bugs in output formatting.

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