Programming PHP

echo "$who was $where";
Kilroy was here
The complex way is to surround the variable being interpolated with curly braces.
This method can be used either to disambiguate or to interpolate array lookups. The
classic use of curly braces is to separate the variable name from surrounding text:
$n = 12;
echo "You are the {$n}th person";
You are the 12th person
Without the curly braces, PHP would try to print the value of the $nth variable.
Unlike in some shell environments, in PHP strings are not repeatedly processed for
interpolation. Instead, any interpolations in a double-quoted string are processed,
then the result is used as the value of the string:
$bar = 'this is not printed';
$foo = '$bar'; // single quotes
print("$foo");
$bar
Single-Quoted Strings
Single-quoted strings do not interpolate variables. Thus, the variable name in the following
string is not expanded because the string literal in which it occurs is singlequoted:
$name = 'Fred';
$str = 'Hello, $name'; // single-quoted
echo $str;
Hello, $name
The only escape sequences that work in single-quoted strings are \', which puts a single
quote in a single-quoted string, and \\, which puts a backslash in a single-quoted
string. Any other occurrence of a backslash is interpreted simply as a backslash:
$name = 'Tim O\'Reilly'; // escaped single quote
echo $name;
$path = 'C:\\WINDOWS'; // escaped backslash
echo $path;
$nope = '\n'; // not an escape
echo $nope;
Tim O'Reilly
C:\WINDOWS
\n
Double-Quoted Strings
Double-quoted strings interpolate variables and expand the many PHP escape
sequences. Table 4-1 lists the escape sequences recognized by PHP in double-quoted
strings.
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Quoting String Constants | 73