问题
A. What does this do?
require ("./file.php");
B. in comparison to this?
require ("file.php");
(Its not up-one-directory.. which would be)
require ("../file.php");
回答1:
./ is the current directory. It is largely the same as just file.php, but in many cases (this one included) it doesn't check any standard places PHP might look for a file, instead checking only the current directory.
From the PHP documentation (notice the last sentence):
Files for including are first looked for in each include_path entry relative to the current working directory, and then in the directory of current script. E.g. if your include_path is libraries, current working directory is /www/, you included include/a.php and there is include "b.php" in that file, b.php is first looked in /www/libraries/ and then in /www/include/. If filename begins with ./ or ../, it is looked only in the current working directory.
回答2:
The first version forces the internal mechanism to include files relatively to the... directly executed file. So for example you have
index.php
// directly executed script (php -f index.php or from a browser)
include 'second.php';
second.php
// This is included relatively to index.php
// Actually, it is first searched relatively to include_path, then relatively
// to index.php
include './third.php';
third.php
// This is included relatively to second.php ONLY. It does not search
// include_path
return "foo";
回答3:
The Short Answer
You're right, it's not up one directory. A . refers to the directory you're in, and .. refers to the parent directory.
Meaning, ./file.php and file.php are functionally equivalent in PHP. Here's the relevent page of documentation: http://us.php.net/manual/en/wrappers.file.php
The Longer Answer
However, just because they work the same in this context doesn't mean they're always the same.
When you're operating in a *nix shell environment, and you type the name of an executable file, the shell will look in the PATH directories, but it won't look in the CWD, or the directory you're currently in.
So, if you're in a directory that has a file called: myprogram.php (this would be a PHP CLI file) and you just type:
myprogram.php
it doesn't matter if your program is executable or not. The shell will look in /bin/, /usr/bin/ etc for your file, but it won't look in ./, or the directory you're in.
To execute that program without adding your directory to the PATH, you need to type
./myprogram
So really, ./ is more explicit. It means, "the file you're looking for HAS to be right here" and no ./ means, "the file should be somewhere the program looking for files".
回答4:
The dot-slash forces the file to be found in the current directory only, rather than additionally searching the paths mentioned in the include_path setting.
回答5:
Simply you are telling php to include the file in the current directory only or fail if the file is not present.
If you use the format "indexcommon3.php" and the file is not present php will search it into the include_path system variable.
For reference you can use http://www.php.net/manual/en/function.include.php
回答6:
Edit: I totally rewrited the answer for the sake of clarity
When including a file, you can either use ./myfile.php or myfile.php.
They are not the same and you should always, preferibly, use the first syntax, unless you know what you're doing.
The difference is best ilustrated with an example: lets say you have the following files and folder structure:
index.php
inc/inner.php
From index.php, you can include your inner template without the ' ./' and it will work as expected:
# index.php
<?php
include "inc/inner.php";
Now let's say we add a new file, so the folder structure is now like this:
index.php
inc/inner.php
inc/inner-inner.php
To include inner-inner.php in inner.php, we would do this... right?
# src/inner.php
<?php
include "inner-inner.php";
Wrong. index.php will just look for inner-inner.php *in the root folder`.
index.php
inc/inner.php
inc/inner-inner.php
* inner-inner.php <- Doesn't exist, PHP ERROR.
Instead, we should use the ./ syntax to include inner-inner. This will instruct that the file we are including must be included relative to the current file, not to the current "entry point" of the PHP script.
# src/inner.php
<?php
include "./inner-inner.php";
In addition, and as mentioned in other comments, if you have configured a different "load path" for your PHP application, that load path wwill be looked up first without the ./ syntax. Instead, the ./ syntax is more efficient because it doesn't check the "include path" of php.
If you wanna make your includes even more explicit, use the __DIR__ constant. This tells php: "Print the current directory in which this file is".
# src/inner.php
<?php
include __DIR__ . "/inner-inner.php";
TLDR; Always use ./ or __DIR__ because it's relative to the working directory and doesn't deppend on the php's "include path".
回答7:
It's explicitly naming the current directory.
来源：https://stackoverflow.com/questions/579374/what-does-the-dot-slash-do-to-php-include-calls