String Theory - Secret Agent Man (
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We'll begin right at the top, with some very basic
definitions and concepts.
In PHP, the term "string" refers to a sequence
of characters. The following are all valid examples of strings:
"ciao"
"I ROCK!"
"a long time ago in a galaxy far, far away"
String values can be assigned to a variable using the
standard assignment operator.
<?
$identity = "Spiderman";
?>
String values may be enclosed in either double quotes ("") or
single quotes('') - the following variable assignments are equivalent"
<?
$car = "Porsche";
?>
<?
$car = 'Porsche';
?>
String values enclosed in double quotes are automatically
parsed for variable names; if variable names are found, they are automatically
replaced with the appropriate variable value.
<?
$identity = "James Bond";
$car = "BMW";
// this would contain the string "James Bond drives a BMW"
$sentence = "$identity drives a $car";
?>
PHP also allows you to create strings which span multiple
lines. The original formatting of the string, including newlines and whitespace,
is retained when such a string is printed.
<?
// multi-line block
$html_output = <<<EOF
<html>
<head></head>
<body>
<ul>
<li>vanilla
<li>chocolate
<li>strawberry
</ul>
</body>
</html>
EOF;
?>
The <<< symbol indicates to PHP that what comes next
is a multi-line block of text, and should be printed as is right up to the
marker "EOF". In PHP-lingo, this is known as "here document" syntax, and it
comes in very handy when you need to output a chunk of HTML code, or any other
multi-line string.
Strings can be concatenated with the string
concatenation operator, represented by a period(.)
<?
// set up some string variables
$a = "the";
$b = "games";
$c = "begin";
$d = "now";
// combine them using the concatenation operator
// this returns "the games begin now"
$statement = $a . " " . $b . " " . $c . " " . $d;
// and this returns "begin the games now!"
$command = $c . " " . $a . " " . $b . " " . $d . "!";
// this also returns "begin the games now!"
$command = "$c $a $b $d!";
?>
Note that if your string contains quotes, carriage returns or
backslashes, it's necessary to escape these special characters with a backslash.
<?
// will cause an error due to mismatched quotes
$film = 'America's Sweethearts';
// will be fine
$film = 'America\'s Sweethearts';
// will generate an error
$story = "...and so he said, "backslash me, knave!"";
// will be fine
$story = "...and so he said, \"backslash me, knave!\"";
?>
The print() function is used to output a string or string
variable.
<?
// string
print "Jeepers Creepers";
// string variable
$film = "Jeepers Creepers";
print $film;
?>
PHP also offers the echo() construct, which does the same
thing.
<?
// string
echo "Shakespeare";
// string variable
$author = "Shakespeare";
echo $author;
// combine the two
echo "Despite what critics may say, $author's influence can be felt even
today";
?>
Since displaying variable values is one of the most
fundamental things you can do, PHP also offers a shortcut syntax (similar to
that offered by JSP) to simplify this task. The following two statements are
equivalent:
<?
$author = "Shakespeare";
echo $author;
?>
<?=$author?>
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