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What is the difference between single-quoted and double-quoted strings in PHP?

stackoverflow.com › questions › 3446216 › what-is-the-difference-between-single-quoted-and-double-quoted-strings-in-php

PHP strings can be specified not just in two ways, but in four ways.

Single quoted strings will display things almost completely "as is." Variables and most escape sequences will not be interpreted. The exception is that to display a literal single quote, you can escape it with a back slash \', and to display a back slash, you can escape it with another backslash \\ (So yes, even single quoted strings are parsed).
Double quote strings will display a host of escape sequences (including some regexes), and variables in the strings will be evaluated. An important point here is that you can use curly braces to isolate the name of the variable you want evaluated. For example let's say you have the variable $type and you want to echo "The $types are". That will look for the variable $types. To get around this use echo "The {$type}s are". Take a look at string parsing to see how to use array variables and such.
Heredoc string syntax works like double quoted strings. It starts with <<<. After this operator, an identifier is provided, then a newline. The string itself follows, and then the same identifier again to close the quotation. You don't need to escape quotes in this syntax.
Nowdoc (since PHP 5.3.0) string syntax works essentially like single quoted strings. The difference is that not even single quotes or backslashes have to be escaped. A nowdoc is identified with the same <<< sequence used for heredocs, but the identifier which follows is enclosed in single quotes, e.g. <<<'EOT'. No parsing is done in nowdoc.

Notes: Single quotes inside of single quotes and double quotes inside of double quotes must be escaped:

$string = 'He said "What\'s up?"';
$string = "He said \"What's up?\"";

Speed:
There is no difference.
Please read a credible article on the matter from one of PHP core developers. Speaking of tests, one should never take them for granted. It must be understood that writing a credible test and, especially, interpreting its results requires a lot of knowledge and experience. Which means that most tests out there are just bogus. For example, in a code like this

for(i<100000;$i++) {
    'string';
}

The quoted string gets parsed only once, along with entire script, and then gets translated into opcode. Which is then gets executed a million times. So it measures anything but parsing. And that's only a tip of the iceberg. For a nanobenchmark like this, it's practically impossible to create a credible test that wouldn't be spoiled by some interfering side effect.

Answer from Peter Ajtai on Stack Overflow

PHP

php.net › manual › en › language.types.string.php

PHP: Strings - Manual

Unlike the double-quoted and heredoc syntaxes, variables and escape sequences for special characters will not be expanded when they occur in single quoted strings. ... <?php echo 'this is a simple string', PHP_EOL; echo 'You can also have embedded newlines in strings this way as it is okay to do', PHP_EOL; // Outputs: Arnold once said: "I'll be back" echo 'Arnold once said: "I\'ll be back"', PHP_EOL; // Outputs: You deleted C:\*.*? echo 'You deleted C:\\*.*?', PHP_EOL; // Outputs: You deleted C:\*.*? echo 'You deleted C:\*.*?', PHP_EOL; // Outputs: This will not expand: \n a newline echo 'This will not expand: \n a newline', PHP_EOL; // Outputs: Variables do not $expand $either echo 'Variables do not $expand $either', PHP_EOL; ?>

W3Schools

w3schools.com › php › php_string.asp

PHP Strings

// Using double quotes $x = "John"; echo "Hello $x\n"; echo "\tHow are you?\n"; // Using single quotes $x = 'John'; echo 'Hello $x\n'; echo '\tHow are you?\n'; Try it Yourself » · For a complete reference of all string functions, go to our complete PHP String Reference.

Discussions

How to include single quotes in the value of a text string - PHP - SitePoint Forums | Web Development & Design Community

Hi I have a script that writes values to a php text file that works almost fine as in :- $content = '$security_code = '. $short_string . ';'."\n"; fwrite($txtfile, $content); and writes a line to a text file as $security_code = BA1EF7; Only problem is I want it to write to the file as follows ... More on sitepoint.com

sitepoint.com

0

February 15, 2021

PHP double quote/single quote/string/array interaction

Not sure what the question is, but see https://www.php.net/manual/en/language.types.string.php Note: Unlike the double-quoted and heredoc syntaxes, variables and escape sequences for special characters will not be expanded when they occur in single quoted strings. . = concatenation... it joins two strings 'foo' . 'bar' results in "foobar" I know that . is for concatenation can you mind explaining the purpose of the dots and the quote marks? you're building the javascript array echo "[ '".$row['gender']."' , ".$row['number']." ] ,"; outputs ['male', 42], ( "['" + gender + "', " + number + "]," ) maybe do echo json_encode(array($row['gender'], $row['number'])); instead More on reddit.com

r/PHPhelp

7

0

June 22, 2021

Question: Why do PHP developers hate sprintf()?

I think most people disagree that sprintf() is more concise, and instead view it as unneeded complexity. $feelThings = $goodEmotion ? "happy" : "sad"; $s = "My $spouse has $petNumber $petType and that makes me $feelThings"; Kinda like disliking ternary operators within other constructs...personal preference! More on reddit.com

r/PHPhelp

30

12

January 5, 2022

PHP syntax highlighting between HTML quotes

But i just can’t seem to find how it’s possible to get the right PHP syntax highlighting when working with a PHP / HTML combination. And that’s kind of important. One may use PHP code inside HTML quotes like in the screenshot, but the the PHP syntax isn’t right anymore. The screenshot ... More on forum.sublimetext.com

forum.sublimetext.com

0

March 8, 2013

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Stack Overflow

stackoverflow.com › questions › 3446216 › what-is-the-difference-between-single-quoted-and-double-quoted-strings-in-php

What is the difference between single-quoted and double-quoted strings in PHP? - Stack Overflow

Top answer

1 of 7

1252

PHP strings can be specified not just in two ways, but in four ways.

Single quoted strings will display things almost completely "as is." Variables and most escape sequences will not be interpreted. The exception is that to display a literal single quote, you can escape it with a back slash \', and to display a back slash, you can escape it with another backslash \\ (So yes, even single quoted strings are parsed).
Double quote strings will display a host of escape sequences (including some regexes), and variables in the strings will be evaluated. An important point here is that you can use curly braces to isolate the name of the variable you want evaluated. For example let's say you have the variable $type and you want to echo "The $types are". That will look for the variable $types. To get around this use echo "The {$type}s are". Take a look at string parsing to see how to use array variables and such.
Heredoc string syntax works like double quoted strings. It starts with <<<. After this operator, an identifier is provided, then a newline. The string itself follows, and then the same identifier again to close the quotation. You don't need to escape quotes in this syntax.
Nowdoc (since PHP 5.3.0) string syntax works essentially like single quoted strings. The difference is that not even single quotes or backslashes have to be escaped. A nowdoc is identified with the same <<< sequence used for heredocs, but the identifier which follows is enclosed in single quotes, e.g. <<<'EOT'. No parsing is done in nowdoc.

Notes: Single quotes inside of single quotes and double quotes inside of double quotes must be escaped:

$string = 'He said "What\'s up?"';
$string = "He said \"What's up?\"";

Speed:
There is no difference.
Please read a credible article on the matter from one of PHP core developers. Speaking of tests, one should never take them for granted. It must be understood that writing a credible test and, especially, interpreting its results requires a lot of knowledge and experience. Which means that most tests out there are just bogus. For example, in a code like this

for(i<100000;$i++) {
    'string';
}

The quoted string gets parsed only once, along with entire script, and then gets translated into opcode. Which is then gets executed a million times. So it measures anything but parsing. And that's only a tip of the iceberg. For a nanobenchmark like this, it's practically impossible to create a credible test that wouldn't be spoiled by some interfering side effect.

2 of 7

256

Things get evaluated in double quotes but not in single:

$s = "dollars";
echo 'This costs a lot of $s.'; // This costs a lot of $s.
echo "This costs a lot of $s."; // This costs a lot of dollars.

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TinyMCE

tiny.cloud › blog › php-escape

How to work with PHP escape quotes and characters | TinyMCE

December 7, 2023 - Master PHP escape sequences with our guide. Learn string escape basics, single vs double quote usage, and how to navigate heredoc syntax.

Droptica

droptica.com › blog › combining-string-literals-and-variables-php

Combining strings and variables in PHP 8+: examples and common mistakes

PHP gives you four common ways to build dynamic strings: concatenation with single quotes, interpolation inside double quotes, sprintf() formatting and heredoc/nowdoc blocks. Each has different readability, escaping rules and maintenance cost.

DEV Community

dev.to › realflowcontrol › too-double-quote-or-not-thats-the-question-78l

To double quote or not, that's the question! - DEV Community

August 23, 2024 - This feature is limited to strings in double quotes and heredoc. Using single quotes (or nowdoc) will yield a different result: $juice = "apple"; echo 'They drank some $juice juice.'; // will output: They drank some $juice juice. Look at that: PHP will not search for variables in that single quoted string.

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CodeBasics

code-basics.com › programming › php course › quotes

CodeBasics | Quotes | PHP

In other words, anything inside quotes is considered a string, even if it's just a space or nothing at all. If you display strings on the screen, 'Hello' and 'Goodbye' will be clearly visible. But ' ' and '' can be confusing, because printing an empty string looks like a complete absence of output, while a string with a space shows "empty space" that is visually hard to tell apart. PHP, however, clearly distinguishes between them.

GeeksforGeeks

geeksforgeeks.org › php › what-is-the-difference-between-single-quoted-and-double-quoted-strings-in-php

What is the difference between single-quoted and double-quoted strings in PHP? - GeeksforGeeks

April 10, 2022 - Double-quoted strings: By using Double quotes the PHP code is forced to evaluate the whole string. The main difference between double quotes and single quotes is that by using double quotes, you can include variables directly within the string. It interprets the Escape sequences.

SitePoint

sitepoint.com › php

How to include single quotes in the value of a text string - PHP - SitePoint Forums | Web Development & Design Community

February 15, 2021 - Hi I have a script that writes values to a php text file that works almost fine as in :- $content = '$security_code = '. $short_string . ';'."\n"; fwrite($txtfile, $content); and writes a line to a text file as $security_code = BA1EF7; Only problem is I want it to write to the file as follows $security_code = 'BA1EF7'; ie value enclosed in single quotes - any suggestions please

reddit.com › r/phphelp › php double quote/single quote/string/array interaction

r/PHPhelp on Reddit: PHP double quote/single quote/string/array interaction

June 22, 2021 -

I've been fiddling google charts for a while now for my project, watching youtube videos trying to copy and learn how to do it.

The problem was my chart will only show "Other" and only a grey, 100% pie instead of showing the Male/Female division from my database table.

I somehow got into the conclusion that the chart wont read the "number" from the query, since I used an AS statement on my SQL line, so I tried to search for solutions on how to transform the array into int but I dropped since they seemed to be complex and I was just starting how to get here.

I've been stuck for days but i finally solved it when I decided to abandon the learning for a bit and straight out copy the code from the video, and I noticed that the row[number] part did not need the enclosure of single quotes and it worked like magic.

So somehow the removal of the single quotes "freed" the number and it displayed the chart. What is exactly the explanation behind this? The syntax overwhelmed me a bit cause I was learning JS, HTML, CSS, and PHP all at the same time as I progress. I know in PHP you can use "" or '' for strings, I know that . is for concatenation, but this one uses dots to enclose the array. Or not. Or maybe it was a javascript syntax from the google chart api. Can someone enlighten me about this?

var data = google.visualization.arrayToDataTable([
        ['gender', 'number'],
        <?php
            while($row = mysqli_fetch_array($result))
            {
                echo "[ '".$row['gender']."' , ".$row['number']." ] ,";
            }   
        ?>    
        ]);

// tldr: i used to put ".$row['number']." inside '', like the row gender
and it didnt work. can you mind explaining the purpose of the dots and the
quote marks?