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echo
is not a function but a language construct.
Its arguments are a list of expressions following the
echo
keyword, separated by commas, and not delimited by parentheses.
Unlike some other language constructs,
echo
does not have
any return value, so it cannot be used in the context of an expression.
echo
also has a shortcut syntax, where you can
immediately follow the opening tag with an equals sign. This syntax is available
even with the
short_open_tag
configuration
setting disabled.
I have
<?=$foo?>
foo.
One or more string expressions to output, separated by commas.
Non-string values will be coerced to strings, even when
strict_types
directive is enabled.
Приклад #1
echo
examples
<?php
echo
"echo does not require parentheses."
;
// Strings can either be passed individually as multiple arguments or
// concatenated together and passed as a single argument
echo
'This '
,
'string '
,
'was '
,
'made '
,
'with multiple parameters.'
,
"\n"
;
echo
'This '
.
'string '
.
'was '
.
'made '
.
'with concatenation.'
.
"\n"
;
// No newline or space is added; the below outputs "helloworld" all on one line
echo
"hello"
;
echo
"world"
;
// Same as above
echo
"hello"
,
"world"
;
echo
"This string spans
multiple lines. The newlines will be
output as well"
;
echo
"This string spans\nmultiple lines. The newlines will be\noutput as well."
;
// The argument can be any expression which produces a string
$foo
=
"example"
;
echo
"foo is
$foo
"
;
// foo is example
$fruits
= [
"lemon"
,
"orange"
,
"banana"
];
echo
implode
(
" and "
,
$fruits
);
// lemon and orange and banana
// Non-string expressions are coerced to string, even if declare(strict_types=1) is used
echo
6
*
7
;
// 42
// Because echo does not behave as an expression, the following code is invalid.
(
$some_var
) ? echo
'true'
: echo
'false'
;
// However, the following examples will work:
(
$some_var
) ? print
'true'
: print
'false'
;
// print is also a construct, but
// it is a valid expression, returning 1,
// so it may be used in this context.
echo
$some_var
?
'true'
:
'false'
;
// evaluating the expression first and passing it to echo
?>
Примітки
Зауваження
:
Оскільки це мовна
конструкція, а не функція, її не можна викликати через
змінні-функції
або
названі параметри
.
Зауваження
:
Using with parentheses
Surrounding a single argument to
echo
with parentheses will not
raise a syntax error, and produces syntax which looks like a normal
function call. However, this can be misleading, because the parentheses are actually
part of the expression being output, not part of the
echo
syntax itself.
<?php
echo
"hello"
;
// outputs "hello"
echo(
"hello"
);
// also outputs "hello", because ("hello") is a valid expression
echo(
1
+
2
) *
3
;
// outputs "9"; the parentheses cause 1+2 to be evaluated first, then 3*3
// the echo statement sees the whole expression as one argument
echo
"hello"
,
" world"
;
// outputs "hello world"
echo(
"hello"
), (
" world"
);
// outputs "hello world"; the parentheses are part of each expression
echo(
"hello"
,
" world"
);
// Throws a Parse Error because ("hello", " world") is not a valid expression
?>
Passing multiple arguments to
echo
can avoid
complications arising from the precedence of the concatenation operator in
PHP. For instance, the concatenation operator has higher precedence than
the ternary operator, and prior to PHP 8.0.0 had the same precedence as addition
and subtraction:
<?php
// Below, the expression 'Hello ' . isset($name) is evaluated first,
// and is always true, so the argument to echo is always $name
echo
'Hello '
. isset(
$name
) ?
$name
:
'John Doe'
.
'!'
;
// The intended behaviour requires additional parentheses
echo
'Hello '
. (isset(
$name
) ?
$name
:
'John Doe'
) .
'!'
;
// In PHP prior to 8.0.0, the below outputs "2", rather than "Sum: 3"
echo
'Sum: '
.
1
+
2
;
// Again, adding parentheses ensures the intended order of evaluation
echo
'Sum: '
. (
1
+
2
);
If multiple arguments are passed in, then parentheses will not be
required to enforce precedence, because each expression is separate:
<?php
echo
"Hello "
, isset(
$name
) ?
$name
:
"John Doe"
,
"!"
;
echo
"Sum: "
,
1
+
2
;
print
- Output a string
printf()
- Output a formatted string
flush()
- Flush system output buffer
Ways to specify literal strings
pemapmodder1970 at gmail dot com
¶
7 years ago
Passing multiple parameters to echo using commas (',')is not exactly identical to using the concatenation operator ('.'). There are two notable differences.
First, concatenation operators have much higher precedence. Referring to
http://php.net/operators.precedence,
there are many operators with lower precedence than concatenation, so it is a good idea to use the multi-argument form instead of passing concatenated strings.
<?php
echo
"The sum is "
.
1
|
2
;
echo
"The sum is "
,
1
|
2
;
?>
Second, a slightly confusing phenomenon is that unlike passing arguments to functions, the values are evaluated one by one.
<?php
function
f
(
$arg
){
var_dump
(
$arg
);
return
$arg
;
}
echo
"Foo"
.
f
(
"bar"
) .
"Foo"
;
echo
"\n\n"
;
echo
"Foo"
,
f
(
"bar"
),
"Foo"
;
?>
The output would be:
string(3) "bar"FoobarFoo
Foostring(3) "bar"
barFoo
It would become a confusing bug for a script that uses blocking functions like sleep() as parameters:
<?php
while(
true
){
echo
"Loop start!\n"
,
sleep
(
1
);
}
?>
vs
<?php
while(
true
){
echo
"Loop started!\n"
.
sleep
(
1
);
}
?>
With ',' the cursor stops at the beginning every newline, while with '.' the cursor stops after the 0 in the beginning every line (because sleep() returns 0).
