ASP File Operations
Try the demo or view the source code.ASP provides access to the web server's file system by defining several objects representing drives, folders, files, etc. This article demonstrates the coding basics needed to perform the most common file operations: creating, deleting, reading from and writing to a file.
File access permissions will apply to the script execution, so the user account which it runs under (such as an anonymous ID set up for web users) must have suitable permissions to the files and directories accessed.
Other access permissions may be applied as well, such on Microsoft IIS web servers. Check your system documentation.
The FileSystemObject Object
To access a file, you first create a FileSystemObject which
provides the methods to access, create, delete or open a file for input or
output. All of these methods require you to specify the physical path for the
file.
<% set fs = CreateObject("Scripting.FileSystemObject")
fs.DeleteFile("C:\temp\10312000.txt") %>
To find the path of a file on the local web site, the built-in
Server.MapPath() function can be used to translate a URL to a
physical path.
<% path = Server.MapPath("/webtmp/abc123.txt") %>
Which might return "C:\Inetpub\wwwroot\webtmp\abc123.txt" for example.
Another useful method provided by this object is FileExists()
which returns a value of True or False. This is good
for checking a file's status before attempting to create, delete or open
it.
Creating a Text File
The CreateTextFile() method is used to create a new text file.
Its parameters are described below.
| CreateTextFile(filename [, overwrite [, unicode]]) | |||
|---|---|---|---|
| Parameter | Description | Required | Default |
| filename | String specifying the path and filename. | Yes | n/a |
| overwrite | Boolean flag. If True, any existing file with
the given name is overwritten. |
No | True |
| unicode | Boolean flag. If True, the file is created as
Unicode text file, otherwise ASCII. |
No | False |
The method returns a TextStream object that can then be used
for outputting data, after which the file should be closed to ensure all output
operations are completed. Here's an example.
<% set fs = CreateObject("Scripting.FileSystemObject")
set file = fs.CreateTextFile("C:\temp\10312000.txt", true, false)
file.WriteLine("Hello World!")
file.Close %>
If overwrite is True, any existing file is destroyed and
replaced with the new file. If you don't care about overwriting existing files,
set it to True (the default). Otherwise, it's a good idea to use
FileExists() to check a file's status first, so you can handle the
situation in your code instead of having the method generate an error.
Deleting a File
The DeleteFile() method allows you to delete one or more
files.
| DeleteFile(filespec [, force]) | |||
|---|---|---|---|
| Parameter | Description | Required | Default |
| filespec | String specifying the path and filename. Wildcards can be used on the filename. | Yes | n/a |
| force | Boolean flag. If True, forces files marked
'read-only' to be deleted. |
No | False |
Note that the path can contain wildcard characters, such as "temp*.txt". Here's an example that deletes a single file.
<% set fs = CreateObject("Scripting.FileSystemObject")
fs.DeleteFile("C:\temp\10312000.txt", true) %>
Again, it's a good idea to use FileExists() before attempting
to delete a given file, to prevent any errors.
Reading and Writing Text Files
The OpenTextFile() method opens a file for input or output
depending on the mode chosen.
| OpenTextFile(filename[, iomode[, create[, format]]]) | |||
|---|---|---|---|
| Parameter | Description | Required | Default |
| filename | String specifying the path and filename. | Yes | n/a |
| iomode | One of three constants: ForReading (1),
ForWriting (2) or ForAppending (8). |
No | ForReading |
| create | Boolean flag. If True, the file will be
created if it doesn't already exist. |
No | False |
| format | Tristate flag, one of: TristateUseDefault
(-2), TristateTrue (-1) or TristateFalse (0).
|
No | TristateFalse |
Opening a file for writing causes the current contents to be overwritten. Using the append mode preserves the current file contents, new data is written starting at the end of the file.
If true, the create option cause the file to be created if it doesn't
already exist. If it is created, format specifies whether Unicode
(TristateTrue) or ASCII (TristateFalse) is used. A
value of TristateUseDefault causes it to use whatever the system
default is.