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PHP input/output streams

PHP 3.0.13 and up, php://output and php://input since PHP 4.3.0, php://filter since PHP 5.0.0

  • php://stdin

  • php://stdout

  • php://stderr

  • php://output

  • php://input

  • php://filter

php://stdin, php://stdout and php://stderr allow access to the corresponding input or output stream of the PHP process.

php://output allows you to write to the output buffer mechanism in the same way as print() and echo().

php://input allows you to read raw POST data. It is a less memory intensive alternative to $HTTP_RAW_POST_DATA and does not need any special php.ini directives.

php://stdin and php://input are read-only, whereas php://stdout, php://stderr and php://output are write-only.

php://filter is a kind of meta-wrapper designed to permit the application of filters to a stream at the time of opening. This is useful with all-in-one file functions such as readfile(), file(), and file_get_contents() where there is otherwise no opportunity to apply a filter to the stream prior the contents being read.

The php://filter target takes the following 'parameters' as parts of its 'path'.

  • /resource=<stream to be filtered> (required) This parameter must be located at the end of your php://filter specification and should point to the stream which you want filtered.

    <?php
    /* This is equivalent to simply:
       readfile("http://www.example.com");
       since no filters are actually specified */
    
    readfile("php://filter/resource=http://www.example.com");
     ?>

  • /read=<filter list to apply to read chain> (optional) This parameter takes one or more filternames separated by the pipe character |.

    <?php
    /* This will output the contents of 
       www.example.com entirely in uppercase */
    readfile("php://filter/read=string.toupper/resource=http://www.example.com");
    
    /* This will do the same as above
       but will also ROT13 encode it */
    readfile("php://filter/read=string.toupper|string.rot13/resource=http://www.example.com");
     ?>

  • /write=<filter list to apply to write chain> (optional) This parameter takes one or more filternames separated by the pipe character |.

    <?php
    /* This will filter the string "Hello World"
       through the rot13 filter, then write to
       example.txt in the current directory */
    file_set_contents("php://filter/write=string.rot13/resource=example.txt","Hello World");
     ?>

  • /<filter list to apply to both chains> (optional) Any filter lists which are not prefixed specifically by read= or write= will be applied to both the read and write chains (as appropriate).

Table I-5. Wrapper Summary (For php://filter, refer to summary of wrapper being filtered.)

AttributeSupported
Restricted by allow_url_fopen.No
Allows Reading php://stdin and php://input only.
Allows Writing php://stdout, php://stderr, and php://output only.
Allows Appending php://stdout, php://stderr, and php://output only. (Equivalent to writing)
Allows Simultaneous Reading and WritingNo. These wrappers are unidirectional.
Supports stat()No
Supports unlink()No

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