Open Source Server Side Scripting ECA 236 Open Source Server Side Scripting Files & Directories.

Open Source Server Side Scripting

ECA 236

Open Source Server Side ScriptingFiles & Directories

Open Source Server Side Scripting 2ECA 236

flat filesflat files

2 ways of storing informationflat filesdatabases

advantages of flat filesno specific knowledge of databases requiredno extra charge


flat files cont … flat files cont …

disadvantages of flat filesslow when working with large filessearching is difficult and slowproblems allowing more than one user simultaneous

accessfiles are processed sequentiallydifficult to allow different levels of access


permissionspermissionsdirectory access ( permissions ) may be granted to:

owner: generally has permission to read and writegroups: users can be organized into groupsworld: everyone else

types of file permissionsr readablew writeablex executable


file processingfile processingto write to a file

open the file – create it if it does not already existwrite data to the fileclose the file

to read from a fileopen the file – if it cannot be opened, exit gracefullyread data from the fileclose the file


opening a fileopening a filefopen( ) takes two parameters

the file to be openedthe mode in which to open it

path to file namecreate a variable to hold the path to the file$_SERVER[ 'DOCUMENT_ROOT‘ ] contains the document

root directory$dir_name = dirname($_SERVER["PHP_SELF"]);


opening a fileopening a filepath to file name

create a variable to hold the path to the file$_SERVER[ 'DOCUMENT_ROOT‘ ] contains the document

root directory$dir_name = dirname($_SERVER["PHP_SELF"]);

$doc_root = $_SERVER["DOCUMENT_ROOT"];$dir_name = dirname($_SERVER["PHP_SELF"]);$fp = fopen( $doc_root . $dir_name . "/dogs_1.txt", 'w' ) or die ( “Cannot open the file” );


opening a file cont …opening a file cont …fopen( ) takes 4 parameters the 3rd and 4th are optional

the file to be openedthe mode in which to open itsearch optionoption to open file in remote location

modeindicates the purpose for opening the file

readwrite

> overwrite > append

both


opening a file cont …opening a file cont …

Mode Description

r Read Mode: Open for reading only. Place the file pointer at the beginning of the file.

r+ Read mode: Open for reading and writing. Place the file pointer at the beginning of the file.

wWrite Mode: Open for writing only. Place the file pointer at the beginning of the file. If the file already exists, delete the existing data. If the file does not exist, attempt to create it.

w+Write Mode: Open for writing and reading. Place the file pointer at the beginning of the file. If the file already exists, delete the existing data. If the file does not exist, attempt to create it.

a Append mode: Open the file for appending only. Start from the end of the existing data. If the file does not exist, attempt to create it.

a+ Append mode: Open the file for appending and reading. Start from the end of the existing data. If the file does not exist, attempt to create it.


opening a file cont …opening a file cont …

Mode Description

xCautious Write Mode: Open the file for writing, beginning from the start of the file. If the file already exists, it will not be opened, fopen( ) will return false, and PHP will generate an error.

x+Cautious Write Mode: Open the file for writing and reading, beginning from the start of the file. If the file already exists, it will not be opened, fopen( ) will return false, and PHP will generate an error.

b

Binary Mode: Used in conjunction with one of the other modes. Use this mode if the Operating System differentiates between binary and text files. Windows OS differentiates, Unix OS does not. PHP developers recommend the use of this option for maximum portability. This is the default mode.

tText Mode: Used in conjunction with one of the other modes. This mode is an option only with Windows OS. It is not recommended except before porting the code with the b option.


opening a file cont …opening a file cont …assign the fopen( ) call to a file pointer

use the file pointer to refer to the open fileif the file cannot be opened

the @ operator suppresses the noticedie( ) is called to generate error message and stop execution

of script, thus exiting gracefully

@ $fp = fopen( $file_name, "w" ) or die ( “Cannot open the file” );


writing to a filewriting to a file

fwrite( ) takes three parameters, the third is optional

file pointerstring which will be written to the filemaximum number of bytes

if exceeded, PHP truncates the output string

fwrite( $fp, $string_output, 1000 );


writing to a file cont …writing to a file cont …

separate the sections of data with a delimiterpipe, comma, tab, etcif the data will be used in another application, follow

the rules of the other applicationthe delimiter should not be one which may be used in

the user’s inputend the string with a record separator (newline )

$string_output = “$name|$gender|$height|$weight|$age\n”;


closing the fileclosing the file

use the fclose( ) function to close the filefclose( ) takes one parameter, the file pointer

fclose( $fp );


reading from a filereading from a fileopen the file with the fopen( ) function

use the correct mode to write to the file

@ $fp = fopen( $file_name, “r" ) or die ( “Cannot open the file” );

if ( filesize( "$doc_root/files/file_name.txt“ ) != 0 ){ while( !feof( $fp ) ) {

$line = fgets( $fp, 1000 ); echo $line . “<br />”;

} //end while } // end if

fclose( $fp );


reading from a file cont …reading from a file cont …

if the file opens correctly, read from the file until the end of the file is reached

feof( ) returns TRUE when the end of the file is reached

feof( ) takes one parameter, the file pointer

while( !feof( $fp ) ) {



when using feof( )check to see if the filesize is 0if the filesize is zero an infinite loop is generatedif there is a problem opening the file an infinite loop is

generatedfilesize( ) returns the size of the file in bytes

filesize( ) takes one parameter, the path to the file

if ( filesize("$doc_root/files/file_name.txt" != 0 ){



fgets( ) reads from the file one line at a timefgets( ) takes two parameters, the second is

optionalthe file pointermaximum number of bytes to be returned

fgets( ) returns each line as a string$line = fgets( $fp, 1000 );



fgetss( ) reads from the file one line at a timefgetss( ) takes three parameters, the third is optional

the file pointermaximum number of bytes to be returnedallowable tags

fgetss( ) returns each line as a string, with HTML and PHP removed

$line = fgetss( $fp, 1000 );



fgetcsv( ) reads from the file one line at a timefgetcsv( ) takes four parameters, the third and fourth are optional

the file pointermaximum number of bytes to be returneddelimiter ( defaults to comma )enclosure ( defaults to double quotation marks )

fgetcsv( ) returns each line as an array, separated on the delimiter

$line_array = fgetcsv( $fp, 1000, “|” );



readfile( )opens the fileechoes entire file to browsercloses file

no need to manually open and close file

readfile( ) takes the path to the file as an argument

readfile( "$doc_root/files/file_name.txt" );



file( )opens the filefile is returned as an array, each line as an array element

( newline is still attached )closes file


file( ) takes the path to the file as an argument

$file_array = file( "$doc_root/files/file_name.txt" );



file_get_contents( )opens the filefile is returned as a stringcloses file


file_get_contents( ) takes the path to the file as an argument

$file_string = file_get_contents( "$doc_root/files/file_name.txt" );



fgetc( ) takes one parameter file pointer

fgetc( ) returns one character at a timein addition to string characters, fgetc( ) reads newline

and eof characters

$char = fgetc( $fp );



file_exists( )checks whether a file or directory existsreturns Boolean TRUE if it existsFALSE if it does not

file_exists( ) takes the path to the file as an argument

file_exists( "$doc_root/files/file_name.txt" );



unlink( )deletes a file

unlink( ) takes the path to the file as an argument

unlink( "$doc_root/files/file_name.txt" );


file lockingfile lockingflock( ) takes two parameters

file pointera constant indicating the kind of lock to acquire

Constant Description

LOCK_SH Reading Lock: the file can be shared with other readers.

LOCK_EX Writing Lock: the file cannot be shared. The lock is exclusive.

LOCK_UN Unlock: release the existing lock.


securitysecurityto create a file in a directory above the document

rootmake sure directory exists before writing to ittest it carefully on your server

$doc_root = $_SERVER[ 'DOCUMENT_ROOT' ];$file_name ="$doc_root/../files/file_name.txt";$fp = fopen( $file_name, "w+" );


security cont … security cont … crypt( ) function

one-way algorithm to encrypt a string valueno function to decrypt the string

crypt( ) takes two argumentsstring to be encryptedsalt string

salt does not work the same on different systems


security cont … security cont … crypt( ) function

given the same string and the same salt, the same encrypted result is returned each time

we do not need to know the original value of the encrypted stringcompare encrypted result to password entered by user after

running through the crypt( ) function, with the stored, encrypted password as the salt

if( crypt( $user_entered_pw, $enc_pw_stored ) == $enc_pw_stored ) {

// code if passwords match}

Open Source Server Side Scripting ECA 236 Open Source Server Side Scripting Files & Directories.

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Transcript of Open Source Server Side Scripting ECA 236 Open Source Server Side Scripting Files & Directories.